Rep Power: 424

Yeah, I know this sounds dumb, but I don't like my idle oil pressure. Now that its hot as sin outside, it likes to idle around 12 PSI and I've noticed that below 10 psi and the car likes to stumble and clunk around (and stall), I'd like for it to be higher if I can get it up there. Running down the highway, its fine up in the 70s-low 80s. Temp is 205ish at its hottest (yay 5.5 quarts) sitting in traffic, etc....
I was thinking about dumping 2 or 3 quarts of 5-40 into 2 or 3 quarts of 5-30 to try and bump the hot viscosity up a little more and keep it a little thicker. I don't forsee it doing anything but making the engine run a tad cooler and keep the pressure up.
I'm no chemist, but I looked at the SAE tables and I'm thinking mixing the oils creates a line inbetween the 2 weights... in actual practice is this the case?

 
Rep Power: 315

I was told (true or not) by the oil techs that mixing viscositys will not result in any stable change. ie: 30 = 40 does not equal 35.
Big help hu?

 
Rep Power: 319

humm... this is a little complex being that you are turboed. let me ask a couple of questions.

1. Are you 100% you have enough oil in your system to compensate for your turbo? Are you burning any oil? Is the turbo new, could it have bad seals?

2. have built or done anything with the internals of you engine?

3. What kind of oil are you using right now, weight, brand, synthetic ect.

4. How are you measuring oil pressure? Where is the sensor? If it is in the turbo lines, what is the recommended pressure for that turbo?

5. Have you noticed anything other than the hesitation, weird sounds, valves something like that?

6. Are you still auto crossing this car?

7. How does the oil look/smell when it is removed?

8. How many mile do you go before oil changes, how many autoX miles, and is this your daily driver? How long between oil changes?

9. That temp seems high, is that during autoXing? What octane fuel are you using?


Now to answer your question, as pon55 said, yes, but no Here is why, viscosity of engine oil is determined by the overall molecular size of each molecule of oil. So if the oil molecule gets larger, the oil gets thicker (higher in number). So in principal, when you mix two oils like that, you will get the middle weight (assuming you mix them in a 1:1 ratio). So in that respect your idea of mixing weights and getting the middle weight is correct.

The problem is that oil adsorbs quite a bit of heat, and at some point it will adsorb enough heat to break the carbon bonds in the oil molecules and destroy that oil. This happens from the first time you turn your engine on with new oil. The smaller oil molecules will break first leaving the larger ones. If you get rid of a large portion of small one and leave the larger ones, you have shifted the average size up, and created a thicker oil. So as pon55 said, the weight you have created is not stable. In fact you have shifted a majority of the stress to the thinner oil.

There is also the problem that some companies use additives to adjust the viscosity, this is a cheap way of doing it and generally results short term lived viscosity. I can't say for sure, but I think Royal Purple does this because their oils tend to loose viscosity very quickly for synthetic oil.

 
Rep Power: 424

I'm no chemist, but I get what you said.... it sounds like trying to run straight 5-40 through it once is the ticket, see what happens. I don't think M1 is the thickest stuff in the world anyways.

 
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Dont mix 2 different oil weights or viscosities. They WILL NOT mix properly. You cant put oil in water and expect a 1/2 oil 1/2 water mixture. Liquids don't mix like that.

 
Rep Power: 319

Do these pressure drops happen after the oil has been in for a while or right away after an oil change?

Well, then first thing I would do is send a sample off for testing. Go to blackstone labs and ask for a free sample kit. They'll send you some bottle in the mail. Follow the directions and send them a sample, it costs $20 plus postage. Make sure the oil sample comes striaght from the engine, don't put it into an oil pan then take it out from the oil pan. From here we can see what the viscosity is.

On to different oils. Mobil 1 has always had problems buring in Honda's (it has to do with their piston and ring style). Anyway, I would try switching to Red Line or Amsoil, I always like Red Line myself, althoug these can be tougher to get and more costly. However, you can easily go 6 months on either of these oils even with a turbo, so it should balance out cost wise.

That tempature seems a bit hot for a civic engine, my old cast iron engine ran at those temps though, and from an oil stand point it looks fine. When you say that the standing temp in the pan, you mean the oil pan? If that's the case, you should consider a strong thermally stable oil. How cold does it get where you live? If it is hot all the time, maybe switching to a 10w40 oil will be better for you. Or maybe a 10w40 in the summer and 5w30 in the winter if it gets colder. If you start getting to much of a larger gap between the cold and hot viscosities, the oil has sheering problems and agian looses viscosity very quickly. This is why you want to stay away from oils like 5w40 and 5w50, they won't last that long because the difference in viscosity is to great (in simple terms) and it falls apart very quickly.

So recapping:
1. get a free test kit from blackstone labs
2. get a better syntehtic oil (Red Line or Amsoil), probably 10w40 for the summer months

Hope that helps!


Whether 2 liquids mix or not has to do with their respective surface energies. Water is around 72.8 dynes/cm2 and oil is generally in the 20's and low 30's, it gets lower as it is used. You can find the solubilty (how much one one will go into the other before it can no longer be mixed) of one in the other using these numbers, but i can tell you from experiance these numbers are to far appart to mix well. Now 2 oils will generally have the same surface energy, they are all almost around high 30's intially and the rate at which they drop is an effect from their specific addative. This is why you don't really want to mix different oil brand. Brand A may be at 30 dyne/cm2 after 2000 miles where as Brand B might have lesser additives and be at 15 dynes/cm2 and cause phase seperatioin. But this would only be a problem at start up. Anyway, for the most part a sinlge compnay generally uses the additives in all their oils, so it's not that big a of deal.

 
Rep Power: 424

10-40? Holy crap... you dont think thats a bit thick?
Its warm here, but its not 110 or anything. I just do a lot of traffic sitting which warms things up a bit cuz there's no air flow.
It pulls this crap regardless of the time of change, it likes to do it after driving a while then coming to a stop... highway exits are notorious.

 
Rep Power: 319

well, you where willing to go 5w40.... the first number is for start up, or the oil viscosity at 20C (I think it's 20C, maybe 25...whatever), in going from 5w40 to 10w40 you are only changing the start up conditions. But you will get better life out of the oil, it won't loose viscosity as fast. You could go 10w30 if you wanted too, there isn't much difference between 10w30 and 10w40 in this application. if it was my car, 10w30 Red Line would be what I would use, and if it continues then move up to 10w40. Maybe down to 5w30 during the winter if it gets below freezing.

 
Rep Power: 424

Well yeah, I'm thinking from the startup stand point. It takes a bit of time to warm up 5.5 quarts, the cooler does a pretty good job holding the temp steady so long as it air running through it, but I'd rather not prolong the time it takes to get up to operating temp if possible.
Maybe I need to try the intermediate step and go for 10-30, since its still going to be thicker than 5-30 as far as the composite weight oils go, I'll see if I can frick around with the cooler and such.... I can play with the temperature with tape on the grid etc... if it runs too cool/hot.

 
Rep Power: 319

Well, I wouldn't worry to much about a 10w30 oil weight. Even at startup you are not going have to much of a problem with 10w30. If you look in the owners manual, somewhere there is an oil chart that even says you can use 10 for a cold weight in certian tempature ranges without any problems. I'm pretty confident that a 10w30 will work just fine as long as it is above freezing out.

 
Rep Power: 310

consider yourself lucky mine idles at 3-5 psi and so does my friends supra. but i got the oil cooler sittin here to help.
anyways for your question, like everyone said mixing oils wont do what you want it to do, im using 10w30 royal purple and no extreme problems of any sort.

 
Rep Power: 286

This is simply not true. when mixing a 5w-30 and 5w-40 you may not get a perfect balance between the two, but there is no harm in trying.

 
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actually, oil does mix. just be certain to use the same brand. if you combine different weight oils, you will actually get a sum/average of their differences as the final viscosity.

 
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Dam fish you gotta oil degree??? It makes sense a buddy of mine has a stock turbo 4cyl its a dodge turbo2 he runs a thicker oil and claims it helps with his heat infact its an oil made for turbos i dunno which one. He also said that his turbo fries his oil quicker so he changes it more often. Which would bring absolute truth to what jrfish said.

 
Rep Power: 319

lol close to a degree. I have a Master's in Chemical Engineering, which was a field designed for crude oil manufacturing, rather it be for gas or oil.

 
Rep Power: 314

I’m in Phoenix Arizona Jrfish it 110 out side as I type.

It never gets under 60 in the summer.

My oil is sometimes blackish, would you recommend I use 10w-40.

Currently I use Castrol Synthetic 5w-30.

Thanks in advance!

 
Rep Power: 319

The blackish color is fine, that is carbon suspended in the oil. If this carbon was not suspended, that means it would be deposited in the engine. In fact, if you take the oil out and it's clear, you need to be worried.

In you situation, I would use 10w30. The second number is the hot viscosity, which I wouldn't go above 30 for in a stock car, but the cold number could be risen a bit if your in a hot area all the time, so I would say 10 would be good.

 
Rep Power: 314

Thank You Sir!

 
Rep Power: 288

hey Jr...my dog has been shitting these black things recently....she usually ***** green...should I be worried? hehe


you're always the man to turn to for oil

 
Rep Power: 319

lol, well, maybe you should try feeding her green crayons. My dog used to eat crayon, and you could always see what color he ate the day before.

 
Rep Power: 247

Do not mix oils. it is not good for your engine but its not bad. only do it if your miles away from a store and need oil. and 5w-40 is way to thick i think. i have a 78f250 also and it has a 400 in it. i run 5w-30 in it during the winter and 10-w30 in the summer. keep that in mind.