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Ok, it seems like we have a LOT of different views about oils and their functions.
My name is Ray and I am a senior mechanical engineering student.
I've had my fair share of chemistry classes, but I will be focusing on the mechanical aspects of oil and of course the mechanical properties of your engine since that is my major.
Jrfish007 has agreed to focus on the chemical properties of oil.
The heat transfer basics:
Oil is not just for lubrication. Oil is the most important thermo transfer substance that your car has. The antifreeze/water mixture you have only gets secondary heat that has to move through the metal engine walls before reaching the liquid. Your oil on the other hand is right there where the heat is being created and therefore has the opportunity to move more heat away at a faster rate. Your oil can get a lot hotter than your coolant does.
Thinner oils will heat up and cool down quicker than thicker oils. However; thinner oils are not able to hold as much energy (heat) as thicker (denser) oils. Also, oils that are to thick or dense will not heat up fast enough (taking heat away from the engine) or cool down fast enough. Thicker oils can also create heat do to friction. You need to have a balanced viscosity.
For our cars anything with a viscosity below 5w may not be holding enough energy for a good heat transfer and anything above 40w may not be soaking up enough heat and anything above 30w may even generate heat.
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Jrfish007 and I will keep adding info to this thread. I encourage others, who really know what they are talking about, to do it as well. When we are done we can edit it all to make it reader friendly then re-post it.
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When the engine heats up, and the oil becomes hot, there is not much a different between 5w-20 and 5w-30 i can gaurantee that, the 5w-30 just adds a bit more of protection because its thicker, but you sacrifice the better mileage you get out of the 5w-20 and also the easier flowing start ups. Of course the thicker oil will not break down as easy under heat, giving added protection. And i drive my car hard as **** so thin 5w-20 is not good enough when its hot like this.
congrats. we already have a FAQ at the top of the forum covering this kind of material. and it's covered by someone who isn't a student, but is an engineer/tribologist and has been for many years.
and since an engineer who is knowledgeable about oil wouldn't make such statements as "synthetic gives you more HP" and "no conventional oil is as good as synthetics", you will have to pardon my skepticism. not to mention you already have some incorrect/misleading information in your first post... if this thread continues with such misinformation I will point out the technical reasons and cite examples why it's incorrect, and I will close the thread.
what's next? we should always do 3000 miles oil changes?
Last edited by S2000man01; 07-27-2005 at 06:08 PM.
Oh and in case you weren't aware of what a tribologist is.
Quote:
Mechanical Engineer, Tribologist: Lubrication, friction, and wear (tribology) of mechanical systems; with special interests in machine design, scuffing and seizing mechanisms, and failure analysis. The science of the mechanisms of friction, lubrication, and wear of interacting surfaces that are in relative motion.
yeah... someone who has done this for 30 years would have NO idea what they're talking about compared to the vast and infinite knowledge an engineering student has.
Last edited by S2000man01; 07-27-2005 at 06:09 PM.
When the engine heats up, and the oil becomes hot, there is not much a different between 5w-20 and 5w-30 i can gaurantee that, the 5w-30 just adds a bit more of protection because its thicker, but you sacrifice the better mileage you get out of the 5w-20 and also the easier flowing start ups. Of course the thicker oil will not break down as easy under heat, giving added protection. And i drive my car hard as **** so thin 5w-20 is not good enough when its hot like this.
Correct.
5w-20 and 5w-30 is very close to each other. 30 will give a touch better heat protection and 20 will give you a slightly better HP and MPG.
Remember though that when both are hot the 20 is still lighter than the 30. They never are the exact same oil unless the additives are designed to make them that way (jrfish007 will cover that).
I'm going to cover friction next, which will explain exactly why oils have different effects on HP and MPG from that aspect.
My posts will be interesting and factual. I guarantee you that.
What I know about engineering has nothing to do with this. You're not arguing with me.
Again, who to trust?
An engineer and tribologist who has been doing his job for 30 years as an engine oil expert? Or a wet-behind-the-ears engineering student who knows only what he's been taught in class and has little to no real world experience....
By the way, this statement here:
Quote:
For our cars anything with a viscosity below 5w may not be holding enough energy for a good heat transfer and anything above 40w may not be soaking up enough heat and anything above 30w may even generate heat.
Not correct. You're making it sound as though using a heavier oil is giong to generate heat and that's simply not the case. You were right in your previous paragraph and should have left it at that. Thicker oils can hold more heat, but also take longer to dissipate it.
If you can remove statements like that, and continue to post factual information rather than misleading or outright false information, then we can edit out all the rest of this crap and add it to the FAQ.
But again, this means no more blanket statements such as "no conventional oil protects as good as synthetic" or any of that crap, because then you're just plain wrong.
Again, none of this information is my own. it's from the words of other engineers who specialize in these things and have real world experience.
__________________
Last edited by S2000man01; 07-28-2005 at 08:50 AM.
Alright, Please remember 2 things: 1. my major is in catalysis and fuel cells, not oil and 2. oil companies consider much of information about specific additive and methods to be a trade secret, hence I do not know it. But I have taken classes taught by the chemist and engineers that produce/test motor oils (mostly from Amsoil).
Also, as I stated, any information I post is basically off memory, if need be, I will look up/research certain topics further. I welcome any corrections to my posts that anyone can offer. I certainly understand I do NOT know everything about oil, and as I stated this is not my specialty. I actually work on catalyst (the same in your catalytic converter) and fuel cells, if you have questions about those I can certainly try to answer those.
Detergents:
The purpose: Detergents serve 2 basic purposes, 1. they lower surface tension and 2. keep carbon from depositing on your engine by keeping it in suspension.
1. The first part about lowering surface tension is designed to simply make it flow easier, fluids with high surface tensions tend to form droplets rather than be dispersed. So when the oil “splashes” up against the engine in the crank case, it will be more likely to create a thin film rather than a bunch of droplets, you obviously want a thin film to protect all your engine parts.
2. The second function is more important when oil is flowing through tubes (also in the engine, but more important in flow restricted areas). During the combustion cycle, carbon is produced and small amounts make past the cylinder rings, this small amount can build up over time. Build up is generally the worst where you have a high pressure line that suddenly drops to low pressure, in other words think of you arteries with cholesterol, cholesterol build and build until eventually you can not pump enough blood through to sustain your heart and it stops. The same thing can happen to your engine, if the carbon starts coming out of suspension, it can build on the sides of tubes (like the oil that feeds oil to the heads) and restrict the flow until the heads don’t get enough oil and seize, it will probably get severely damaged and break first, but in any case it’s bad.
So, detergents are necessary in today’s engines, with out them your engine will would be in grave danger (unless you constantly change your oil). Over time and use in your engine, these detergents will start to break down, when this happens, the oil will start to lose its ability to suspend the carbon.
A common myth explained: Okay, this doesn’t sound like a detergent question, but it actually is: Is it okay to switch from organic oil to synthetic?
This myth actually comes from when detergent oil came out, and all the car buffs in their ’67 Camaro switched to detergent oil. The answer is this: If you have a car that has carbon deposits in it (used non-detergent oil, generally in older cars) then put detergent oil in it, you will soften the deposits and they may come lose, think of a blood clot that is fine then comes lose and gives you a heart attack. This is a very real problem, but if you always use detergent oil, you have nothing to worry about.
So what are the detergents that are used in motor oils? Well, that is a trade secret of every oil company. If they told you what was in the oil, their competitors would use it. There are some common things used, so here is small incomplete list (I believe Amsoil has a site with very similar information on it, I took a class from one of the engineers at Amsoil, and well he knew far more than what I have listed below, this is all he could tell us (this a direct copy out of my notes), I do know some of the reactions going here, so for those interested please ask):
Additives used to protect the surface of the engine:
-Detergents used for ware and tare resistant: various phosphates, organic sulfur and chlorine compounds, sulfurized fats, sulfides and disulfides
-Rust and corrosion inhibitors: zinc dithiophosphates, metal phenolates, fatty acids and amines
-Build up inhibitors: metallo-organic compounds of sodium, calcium and magnesium phenolates, phosphonates and sulfanates
-Dispersatents: alkylsuccinimides and alkylsuccinic esters (these are extremely polar molecules that help keep the carbon conglomerating and forming clump)
-Friction modifiers: organic fatty acids and amides, high molecular weight organic phosphorus and phosphoric acid esters
Additives that help in protecting your oil from doing “bad” things:
-Antifoaming additives (these also help lower surface tension): silicone polymers or organic copolymers
-Antioxidants (oil can be oxidized which terminates the free radical reactions that happen that allow it to suspend carbon and disperse it): Zinc dithiophosphates (yes it’s multi functional), hindered phenols, aromatic amines and sulfurized phenols
-Catalyst deactivators (some metals can cause an accelerated rate of oxidation and hence ruin your oil, these form a protective coating around them so that they can not catalyze the oxidation reaction): organic complexes containing nitrogen or sulfur, amines, sulfides and phosphates
Additives used to increase the oils performance:
-These are used to fight wax and wax build up, (wax is often found in organic oil and some synthetics that use the Fischer-Trope synthesis followed by class III hydro cracking): alkylated napthalene and phenolic polymers, polymethacrylates, and certain copolymer esters.
-a seal swell additive, this can expand some metal and polymer seals to help seal better: Organic phosphates and aromatic hydrocarbons
-Oil thinning prevention (as the temperature oil rises it tends to thin out, these additives expand to help fight this and keep the oil at a constant viscosity): Organic phosphates, aromatic hydrocarbons, MMA, dienes and alkylated styrenes
It is absolutely correct. All friction generates heat. The thicker the oil the more internal friction the molecules create and the more heat IT generates. However, if it doesn't generate too much heat, it will still be able to consume energy (remove heat) from the engine at a decent rate.
I do not know at what exact viscosity point where oil in our cars create to much energy from friction and the oil starts consuming less energy. Only extensive testing with the CIVIC's engines will give you that data. Honda is probably the only ones who have done it. Since they once recommended 30w, I'm willing to GUESS that the viscosity max would be around 50w. Why 50w? Because when you engineer something you design a safety factor into it and since old oxidized/evaporated 30w can act like 40w or higher, you make sure 40w to 50w can safely be handled by the engine for at least short periods of time. Of course, your playing with fire if you put anything higher than 30w in your car unless you REALLY know what you are doing and know exactly what will happen.
Please, if I do not make myself clear, call me out on it. I’ll me happy to further explain.
It is absolutely correct. All friction generates heat. The thicker the oil the more internal friction the molecules create and the more heat IT generates. However, if it doesn't generate too much heat, it will still be able to consume energy (remove heat) from the engine at a decent rate.
I do not know at what exact viscosity point where oil in our cars create to much energy from friction and the oil starts consuming less energy. Only extensive testing with the CIVIC's engines will give you that data. Honda is probably the only ones who have done it. Since they once recommended 30w, I'm willing to GUESS that the viscosity max would be around 50w. Why 50w? Because when you engineer something you design a safety factor into it and since old oxidized/evaporated 30w can act like 40w or higher, you make sure 40w to 50w can safely be handled by the engine for at least short periods of time. Of course, your playing with fire if you put anything higher than 30w in your car unless you REALLY know what you are doing and know exactly what will happen.
Please, if I do not make myself clear, call me out on it. I’ll me happy to further explain.
Well, I agree this does happen, but is the heat generated by friction actually going to be enough to heat soak the oil so it can not sufficiently pick up the heat from the cylinders? So I guess the real question is how hot is the oil getting when it is near the cylinder?
-Dispersatents: alkylsuccinimides and alkylsuccinic esters (these are extremely polar molecules that help keep the carbon conglomerating and forming clump)
Carbon has a + ionic polarity. So this is saying that alkylsuccinimides and alkylsuccinic esters have strong - polarities (such as hydrogen and chlorine) to act like a magnets to gather up carbon molecules. Am I correct?
Well, I agree this does happen, but is the heat generated by friction actually going to be enough to heat soak the oil so it can not sufficiently pick up the heat from the cylinders? So I guess the real question is how hot is the oil getting when it is near the cylinder?
Yeah, that’s what I was trying to say. It happens but it's probably pretty far from the saturation point so it is still taking away more heat than it is creating.
I wonder if Honda has info on the actual heat created and what the expected saturation point of oil is expected to be. I'll look. That would be great info to have here.
Last edited by Honda_trilogy; 07-28-2005 at 10:03 AM.
Now for the big topic: Synthetic versus petroleum base oil (aka dino oil)
First lets start with how they are made. Dino oil actually comes from crude oil, that right the same stuff that makes gasoline. Crude oil goes through a process called distillation where smaller particles can be separated from large particles and you can get separate say gasoline, diesel and motor oil. This is a fairly complex process and requires lots of energy and capital and yet is not 100% efficient. When you buy dino oil you are actually buying a variety of oil molecules, some small some large. I’ll revisit this and explain why this is bad in a moment, for now lets look at the synthetic oils. Without getting into to much detail, synthetic oils are very homogenous, that is all the molecules of synthetic oil are about the same size.
SO why does the size of the molecule of oil matter? Smaller molecules have low flash points, or they burn easier and faster. So if you put dino oil into your car, the smaller molecules will burn very quickly (along with many more additives thus creating more build up). Also keep in mind that smaller molecules will thin the oil out, so after you burn off the small molecules, all you have are larger molecules that create a thicker oil, so dino oil can actually thicken after extended periods of use. Since synthetic oil has all the same size molecules, they are not less likely to burn at lower temperatures, but when they do the same size molecules are left, so it does not get thinner or thicker. Dino oil also adds more additives than synthetic additives, when these additives get burned they will create carbon which can thicken the oil, so now you have two ways that the oil is getting thickened.
Because of the uniform molecule size of dino oil, it is generally not recommended in high heat producing engines. For instance, the 4G63 in the Mitsu Evo, it is a small engine producing a large amount of power, lots of power means lots of heat the oil has to soak up. With all this heat being soaked up, dino oils tend to break down very quickly, hence the reason Mitsu says in the owners manual that synthetic oil is required.
jrfish007; what actually happens when oil oxidizes? Is it like rust where oxygen has ionic bonds with other elements to create new molecules? Or does the oxygen pull away elements from the oil like hydrogen (one of oxygen’s favorite friends) and leave behind a different molecule? Since oxygen is a huge element when compared to carbon, hydrogen... does the introduction of oxygen instantly thicken the oil?
If you can't answer that I will understand. You never claimed to be a chemist. It would be good stuff to know and help us all better understand how oil degrades.
Carbon has a + ionic polarity. So this is saying that alkylsuccinimides and alkylsuccinic esters have strong - polarities (such as hydrogen and chlorine) to act like a magnets to gather up carbon molecules. Am I correct?
Great work! That was a lot of fun for me to read!
Yeah, that's right. The key to these guys is that they will break up the a clump of carbon though. They do that buy simply making the carbon have a higher affinty for them than the other carbon, which is pretty amazing considering the carbon carbon bond can become pretty strong. And yet they don't attach to things like metals or the oil (actually they do, but they prefer the carbon, so untill they attach to the carbon the stick to the oil molecules)
Smaller molecules have low flash points, or they burn easier and faster.
Great point!
To use an analogy... you can take a bag of flour a set a match to it and nothing will happen, but flour is very explosive (very low flash point) in it's dust form. The reason is because oxygen is able to easily surround the molecules in the dust stage, and permit fast combustion.
In the same fashion, it is easier for oxygen to react with the oil molecules when they are smaller.
jrfish007; what actually happens when oil oxidizes? Is it like rust where oxygen has ionic bonds with other elements to create new molecules? Or does the oxygen pull away elements from the oil like hydrogen (one of oxygen’s favorite friends) and leave behind a different molecule? Since oxygen is a huge element when compared to carbon, hydrogen... does the introduction of oxygen instantly thicken the oil?
If you can't answer that I will understand. You never claimed to be a chemist. It would be good stuff to know and help us all better understand how oil degrades.
humm.... well if the tripolgist or chemical engineer that works on this one would help, it would be great.
Here is what I do know though, I have worked on coal oxidation, which is similar in that you are breaking down a carbon via oxidation. What happens in coal/carbon oxidation is this: a "loose" carbon will react with the oxygen creating CO or CO2. By loose carbon, imagine a ring of carbon, carbon is conductive so electron flow from place to place, at some point the carbon ring will have a higher density of electrons at one end rather than the other (aka a dipole moment). If oxygen is in the correct place, it will be able to oxidize a carbon and break the ring, once the ring is broken the rest can be easily oxidized also.
Now that is coal, coke and carbon oxidation. Oil I'm going to GUESS oil works in a very similar way where oxygen reacts/removes a single carbon. So then you have a smaller carbon, if this happens once, it's no big deal, but if it happen many times, you can turn a large carbon chain into a small one, which then is easy to burn.
Like I said, I'm applying what I know is PROVEN to something else, this could be wrong, but 99% of the time when oxygen reacts with a carbon molecule, CO2 is produced. It's actually very similar to the combustion process going on inside the cylinder, just much slower.
To use an analogy... you can take a bag of flour a set a match to it and nothing will happen, but flour is very explosive (very low flash point) in it's dust form. The reason is because oxygen is able to easily surround the molecules in the dust stage, and permit fast combustion.
In the same fashion, it is easier for oxygen to react with the oil molecules when they are smaller.
yeah, I think the word you are really looking for is dispersed. Think of a night club, if you have a group of girls dancing together, it is very hard for a guy to get to a girl, but if you take those same girl and disperse them say ten feet apart, the guys will be all over them and many more guys can "hook up". Carbon and oxygen work the same, if the carbon is close together, oxygen can get in to react, but once the carbon is dispersed, carbon and oxygen can hook up and then boom!
Yeah, that's right. The key to these guys is that they will break up the a clump of carbon though. They do that buy simply making the carbon have a higher affinty for them than the other carbon, which is pretty amazing considering the carbon carbon bond can become pretty strong. And yet they don't attach to things like metals or the oil (actually they do, but they prefer the carbon, so untill they attach to the carbon the stick to the oil molecules)
c=c can be the strongest bond (diamonds)
That's one of the reasons why a good filter is so important.
yeah, I think the word you are really looking for is dispersed. Think of a night club, if you have a group of girls dancing together, it is very hard for a guy to get to a girl, but if you take those same girl and disperse them say ten feet apart, the guys will be all over them and many more guys can "hook up". Carbon and oxygen work the same, if the carbon is close together, oxygen can get in to react, but once the carbon is dispersed, carbon and oxygen can hook up and then boom!
The dancing analogy is way better than my flour analogy!
humm.... well if the tripolgist or chemical engineer that works on this one would help, it would be great.
Here is what I do know though, I have worked on coal oxidation, which is similar in that you are breaking down a carbon via oxidation. What happens in coal/carbon oxidation is this: a "loose" carbon will react with the oxygen creating CO or CO2. By loose carbon, imagine a ring of carbon, carbon is conductive so electron flow from place to place, at some point the carbon ring will have a higher density of electrons at one end rather than the other (aka a dipole moment). If oxygen is in the correct place, it will be able to oxidize a carbon and break the ring, once the ring is broken the rest can be easily oxidized also.
Now that is coal, coke and carbon oxidation. Oil I'm going to GUESS oil works in a very similar way where oxygen reacts/removes a single carbon. So then you have a smaller carbon, if this happens once, it's no big deal, but if it happen many times, you can turn a large carbon chain into a small one, which then is easy to burn.
Like I said, I'm applying what I know is PROVEN to something else, this could be wrong, but 99% of the time when oxygen reacts with a carbon molecule, CO2 is produced. It's actually very similar to the combustion process going on inside the cylinder, just much slower.
Since dino oil also has a lot of loose hydrogen in it, I would guess that the oxygen also reacts with the hydrogen, making water. I'm not sure if this would be a problem of any kind since the water would just be turned into steam and escape out the exhaust. Of course, if the old oil is just sitting in you car for long periods, the water can be a catalyst for other oxidations such as your engine rusting.
Since dino oil also has a lot of loose hydrogen in it, I would guess that the oxygen also reacts with the hydrogen, making water. I'm not sure if this would be a problem of any kind since the water would just be turned into steam and escape out the exhaust. Of course, if the old oil is just sitting in you car for long periods, the water can be a catalyst for other oxidations such as your engine rusting.
Actually, this does happen too. But in gasoline cars, there really isn't enough oil for the collection of water to be a problem. However if you look at a deisel engine, my old Power Stroke used 13 quarts per an oil change, you find that when you have that much oil, a thin layer of water can form. It's a big enouggh problem that most deisel trucks have sensors and warning lights dealing with water.
But yes, oxygen loves hydrogen and will pull the hydrogen off also, which then means that oil becomes charged adn then all kinds of wierd thing can happen.
Ok, I have to get to work now and I will be gone for the next few days.
When I return on Monday I plan on addressing the properties of steel and how it is affected by heat and how oil works with the metal in your engine.
Let us know if there is any thing specific that you want us to address. Keep in mind that we have engineering backgrounds but neither of us are oil or engine experts. So we can answer most of the basic stuff but may not be able to get to deep into the science of your particular interest. Engineers are great at researching, so we may still be able to help even if we aren’t to familiar with it.
I think that it's just the basic stuff that we all need to know in order to make good oil decisions anyways. It’s not like we are developing it, we’re just buying the stuff.
Don't worry about the form of this thread being erratic with different topics thrown it no particular order. When this is finished we will do a nice editing job and make it a nice flowing discussion.
Also, I want to again extend our invitation for others to jump in and share their knowledge with us especially if you have a background in this stuff.
Yeah, that’s what I was trying to say. It happens but it's probably pretty far from the saturation point so it is still taking away more heat than it is creating.
exactly.
you stated that heavier oil would generate heat, when technically ALL oil generates heat. the more friction the more heat. but to say that oil generates heat, without stating that unless the oil is already heat saturated, the heat it generates doesn't affect anything, is misleading.
what's next? we should always do 3000 miles oil changes?
No 3000 mile oil changes, unless you are using a non detergent oil, in which case shame on you. However this is a good topic, which has been addressed many times by both of us. So I will put a simple summary of what I've said before.
The answer is simple: I don't know. Here is why, it is dependant, not only the oil you use, but your driving habits, the gas you use and even the air in you area you live/drive in.
Since I can not determine these conditions, I will tell you then oil aspects and you can judge how long you can use your oil.
Dino oil breaks down almost as soon as you put it into your car, so generally speaking, 5,000 miles is good for a dino oil. Some can go a little longer, some not quite as long.
A synthetic oil won't break down nearly as fast, so it can generally last longer. With a synthetic oil, you to change the oil when the additive start to run out or can no longer do there job. Some Amsoil's have been tested up to 18,000 miles and found to be okay, however they still do not recommended going this far. Almost all synthetic that I know of can go at least 5,000 miles, if you want to increase the time between intervals, I highly recommend getting your oil tested after 5,000 miles. This is the only way to know for sure how much life your oil really has.
Just because I say it will last 10k, or this guy who has this degree says it can last this long, nobody knows your exact driving conditions, hence they can tell you what kind of change interval to use.
For instance, I live in Ohio, and Ohio generally has high sulfur gas. Sulfur is really bad stuff for cars, it kills catalytic converters and can speed up oil decay. So I only go 5,000 miles. Now some one in California that doesn't live and dusty area might be able to easily go 10,000 miles, but again I can't stress enough how important it is to get the oil tested if you plan on going over 5,000 miles.
I also only go 5,000 miles because I use dino oil. You might wonder why I do that, well it simple. While synthetic oil gives great advantages and can extend the life of your engine, my car is leased. Frankly it has only got to run 48,000 miles, then I done with it (thank goodness), and dino oil can handle that job.
Now for the big topic: Synthetic versus petroleum base oil (aka dino oil)
First lets start with how they are made. Dino oil actually comes from crude oil, that right the same stuff that makes gasoline. Crude oil goes through a process called distillation where smaller particles can be separated from large particles and you can get separate say gasoline, diesel and motor oil. This is a fairly complex process and requires lots of energy and capital and yet is not 100% efficient. When you buy dino oil you are actually buying a variety of oil molecules, some small some large. I’ll revisit this and explain why this is bad in a moment, for now lets look at the synthetic oils. Without getting into to much detail, synthetic oils are very homogenous, that is all the molecules of synthetic oil are about the same size.
SO why does the size of the molecule of oil matter? Smaller molecules have low flash points, or they burn easier and faster. So if you put dino oil into your car, the smaller molecules will burn very quickly (along with many more additives thus creating more build up). Also keep in mind that smaller molecules will thin the oil out, so after you burn off the small molecules, all you have are larger molecules that create a thicker oil, so dino oil can actually thicken after extended periods of use. Since synthetic oil has all the same size molecules, they are not less likely to burn at lower temperatures, but when they do the same size molecules are left, so it does not get thinner or thicker. Dino oil also adds more additives than synthetic additives, when these additives get burned they will create carbon which can thicken the oil, so now you have two ways that the oil is getting thickened.
Because of the uniform molecule size of dino oil, it is generally not recommended in high heat producing engines. For instance, the 4G63 in the Mitsu Evo, it is a small engine producing a large amount of power, lots of power means lots of heat the oil has to soak up. With all this heat being soaked up, dino oils tend to break down very quickly, hence the reason Mitsu says in the owners manual that synthetic oil is required.
While this is an excellent post, it should be pointed out that the refining of the base stocks for dino oil has become so sophisticated these days, that the severely hydrocracked base stocks and group III oils that conventional oil starts with, are just as good as today's synthetic bases. What makes the differences are the addin packs that companies use and the rest of the process that is maintained to come up with the oil they are selling.
This is why excellent dino oils such as the Havoline GF4 formulations are such an incredible oil. If long drain intervals are not your main concern in an oil, there is no reason to use synthetic when such excellent dino oils are available. In essence, using a good dino oil with change intervals of 5000 miles, is just as effective as using a synthetic with change intervals of 10,000 miles.
No 3000 mile oil changes, unless you are using a non detergent oil, in which case shame on you. However this is a good topic, which has been addressed many times by both of us. So I will put a simple summary of what I've said before.
The answer is simple: I don't know. Here is why, it is dependant, not only the oil you use, but your driving habits, the gas you use and even the air in you area you live/drive in.
Since I can not determine these conditions, I will tell you then oil aspects and you can judge how long you can use your oil.
Dino oil breaks down almost as soon as you put it into your car, so generally speaking, 5,000 miles is good for a dino oil. Some can go a little longer, some not quite as long.
A synthetic oil won't break down nearly as fast, so it can generally last longer. With a synthetic oil, you to change the oil when the additive start to run out or can no longer do there job. Some Amsoil's have been tested up to 18,000 miles and found to be okay, however they still do not recommended going this far. Almost all synthetic that I know of can go at least 5,000 miles, if you want to increase the time between intervals, I highly recommend getting your oil tested after 5,000 miles. This is the only way to know for sure how much life your oil really has.
Just because I say it will last 10k, or this guy who has this degree says it can last this long, nobody knows your exact driving conditions, hence they can tell you what kind of change interval to use.
For instance, I live in Ohio, and Ohio generally has high sulfur gas. Sulfur is really bad stuff for cars, it kills catalytic converters and can speed up oil decay. So I only go 5,000 miles. Now some one in California that doesn't live and dusty area might be able to easily go 10,000 miles, but again I can't stress enough how important it is to get the oil tested if you plan on going over 5,000 miles.
I also only go 5,000 miles because I use dino oil. You might wonder why I do that, well it simple. While synthetic oil gives great advantages and can extend the life of your engine, my car is leased. Frankly it has only got to run 48,000 miles, then I done with it (thank goodness), and dino oil can handle that job.
Dino oil breaks down almost as soon as you put it into your car, so generally speaking, 5,000 miles is good for a dino oil. Some can go a little longer, some not quite as long.
Just because I say it will last 10k, or this guy who has this degree says it can last this long, nobody knows your exact driving conditions, hence they can tell you what kind of change interval to use.
For the first statment. While you are absolutely correct, it should be noted that just because oil has begun breaking down does not mean it is not doing it's job effectively. Saturation is a good term in a sense. A UOA can validate this statement. While all oils break down, their effectiveness and protection level is not saturated until they go beyond a certain level, at which point you should be changing the oil anyways. A UOA of pretty much any dino at say 3000 miles would likely show to still have plenty of life left, and will still protect your engine almost just as effectively as if you had first put it in.
After about 500 miles, the carrier faction oils will have burned out, allowing the addins and the oil to do its job.
