jnapolitano

This one has me stumped. Any help is appreciated.

Bought my 2000 Civic EX automatic at 200K. Did everything I usually do with used cars when I buy them including new water pump with all belts, a new thermostat, new radiator cap (all parts from dealer).

The car appears to have an OEM (but not original) radiator that looks in good condition. All hoses in good condition.

Car uses just a tad bit of coolant per month that I can tell, but no signs of blown head gasket (oil in coolant, excessive coolant usage, etc.). Car does not leak anything.

At about 210K car starts overheating in traffic (entrance to Holland Tunnel no less!). I manage to get off highway and let it cool down, add a little coolant to radiator (reservoir is full, and is always full at all times during this story, btw ). When I hit open road, air flow cools engine down. Next morning car works fine like nothing happened, and drive it back to Virginia just fine.

A few weeks later, same thing. I notice the fan is neurotic. Sometimes comes on when car gets hot, sometimes it doesn't. One I hit open road car cools down. I figure this has to be thermal fan switch, so I replace it ($75 one from dealer, not the cheap $20 thing from the parts store). Top off the coolant, and car runs fine. I figure problem is solved.

About 212K car overheats again, in traffic. I pop into the HOV and get some speed, and car cools down. Once I get off highway into traffic, gauge almost goes to red. I park and check car out. Fan not coming on at all, even when gauge goes to almost red. Let car cool an hour. I pull the electrical connector at the thermal switch and bridge it with a paper clip. Fan now runs, but temp gauge starts climbing to 3/4 mark anyway?

Next morning, after completely cool, I top off radiator (accepts about 16oz. at the most to top off). Car now drives fine, with fan cutting on and off when it should.

I'm at a total loss.

ezone

If you use the paper clip jumper, and try it several times (like 100 times) would it work every time?
I might be suspecting a fan relay has some pitted contacts and isn't turning on every single time.

jnapolitano

Possibly. The thing that got me stumped was even after the car cooled down and I jumped the connector (which forced fan on full-time), the temp still climbed to 3/4.

I'm starting to wonder if the Honda thermostat I put in 12K ago is already failing and sticking closed. Are they failsafe? Would that make sense with the problems I'm having, esp. if thermal switch is located after thermostat on way back to radiator....ie. no boiling coolant to trigger switch to turn fan on.

I also wondered about air pockets, or needing to flush (burp) the system.

Of course I could have just felt upper hose when it was overheating, but I can't seem to remember simple things like that.

ezone

Possibly. The thing that got me stumped was even after the car cooled down and I jumped the connector (which forced fan on full-time), the temp still climbed to 3/4.


Is the temp gauge truly accurate?
Was the fan jumpered to run all the time, and the gauge is still showing high at low road speed? Was the fan actually on at that point?

I'm starting to wonder if the Honda thermostat I put in 12K ago is already failing and sticking closed. Are they failsafe?


No OE stat is failsafe.
In fact, those failsafe thermostats are extremely likely to fail from what I have seen.


Would that make sense with the problems I'm having, esp. if thermal switch is located after thermostat on way back to radiator....ie. no boiling coolant to trigger switch to turn fan on.

Fan switch is in the stat housing. That means that every bit of coolant coming from the radiator must be at 212* (or whatever the turn-on temp is) before the fan turns on.

I also wondered about air pockets, or needing to flush (burp) the system.

You had to add a pint to the radiator. There isn't hardly any reserve capacity as far as extra coolant goes, it needs every last bit to keep the engine cool.
I wonder if this coolant loss was due to getting hot, or if there is a leak, or is it slowly having a head gasket blow?
Of course I could have just felt upper hose when it was overheating, but I can't seem to remember simple things like that.

If the gauge is accurate, then that would only confirm what you already saw on the gauge.



Getting overheated at low road speeds or stopped in traffic (McDs drive thru!) is usually due to either the fan inop, or low coolant levels and the associated issues that go wit low coolant.
I'd start with the low coolant, see why it was low and where it went.

Does it do fine if you keep the radiator full at all times?
Pressure cap on the radiator holds pressure?
Is the system able to suck coolant out of the reservoir and into the radiator as it cools down?


Have you tried washing the core and fins out with a garden hose and sprayer yet?
Wash it towards the front of the car.
See if 200k worth of bugs and dirt and sand are stuck in it.

Thoughts, HTH

jnapolitano

Thanks, ezone, for all the help. You've given me a lot of places to start looking. If the head gasket is going, not much I can do there, however.

You've helped me identify pattern...fan usually starts failing, then car temp gauge climbs, when coolant is slightly low (ie. 8-16oz.) and heat and traffic are added to the mix. After I wait some time and top it off, the car usually runs better, but I just thought it was coincidence, and didn't see how it was related to the fan sketchiness.

Also, the reservoir never moves. It's at the full (high full mark) all the time, whether the car is hot or cold. The car does not suck up anything as it cools down, even when radiator slightly low. Connective hoses are all clear and in good shape. What would this mean?

Thanks again.

ezone

It's not really a pattern, that's just the list of observations.

The reservoir never moving: You mean the radiator was 16oz low and the reservoir was still at the full mark?
That ain't right.

The coolant expands and contracts as it heats and cools. A little bit, I'd guess less than 4oz of change in the reservoir (I've never actually measured, and it varies from car to car.)


There has to be a way for the coolant to get from the bottle to the radiator. Is the hose still attached to the bottom side of the reservoir lid? I see then fall off and drop into the bottle, then the coolant just sits there.
Pinhole anywhere along that line could keep it from sucking back in too.
It's gotta work just like a straw.


OR it may be a radiator and/or radiator cap problem. The cap not only must hold 15 PSI of pressure inside the cooling system, it has to be able to allow flow the other way when the radiator cools and goes into a vacuum. When it gets pressurized and hot, all the excess coolant moves to the bottle. As it cools, it sucks it back out of the bottle.

Make sense?
See if you can figure out where it went wrong on the car.


What is the outside temperature there when the car overheats? Does that have anything to do with it?

jnapolitano

All hoses (incl reservoir hoses) are perfect and in good, unblocked condition, that I can tell. Radiator cap is new, OEM. No coolant leaks I can observe, including when car is overheating. Radiator looks almost new. Car overheats when in traffic/stopped...cools down when I can get it moving at a fair speed again (again, this is only happened a few times, but the few times it has happened, I've almost made the evening news). Outside temp usually moderate to hot, but it's always hot here where I live.

I've got this train of logic in my pea-brain...

1. Slight coolant usage is perhaps from beginning head gasket problem. The car is over 200K, and my last Honda's HG started to go at this time.

2. Is the OEM thermostat, though only 12K old, perhaps periodically sticking or blocked? In my head I'm picturing (at the point of failure) coolant not getting past a closed thermostat, so the fan switch in the housing not detecting the overly hot coolant, since there is none or little to detect (hence the radiator fan not being activated). Also stuck/faulty thermostat contributing to coolant vaccuum system not operating properly between reservoir and radiator.

Please let me know where my logic is faulty, if the above even makes sense. Thanks again for your time, ezone. I'll work with whatever you can give me and go from there.

ezone

All hoses (incl reservoir hoses) are perfect and in good, unblocked condition, that I can tell. Radiator cap is new, OEM. No coolant leaks I can observe,

I guess I have to assume it is ok, since I can't verify for myself if it all actually works.

Wait, no I can't.
You didn't answer this: "You mean the radiator was 16oz low and the reservoir was still at the full mark?"

and

Every time it had overheated, the coolant was low?






This is a problem.




Head gasket leakage (combustion ---> cooling system) could explain it.

Another thought: You added 16oz, but did you run the engine and burp any air out, top off the radiator again before you put the lid on it and drove it?




including when car is overheating. Radiator looks almost new. Car overheats when in traffic/stopped...cools down when I can get it moving at a fair speed again

Dumb question here: Engine hot, radiator fan already running.....Will the engine cool down if you raise the RPM in neutral? This would send me toward poor circulation, like water pump impeller.....or low coolant level.

Turn the heater on full blast, does the engine temp drop? It should, in an overheat. The heater core is an extra radiator. This action could help keep you from ruining your engine.




(again, this is only happened a few times, but the few times it has happened, I've almost made the evening news). Outside temp usually moderate to hot, but it's always hot here where I live.

I've got this train of logic in my pea-brain...

1. Slight coolant usage is perhaps from beginning head gasket problem. The car is over 200K, and my last Honda's HG started to go at this time.
Agree, check into this....Probably would be one of the first things to look for...
HG failed could explain all of it.
But I'm not 100% sure on all your symptoms..



2. Is the OEM thermostat, though only 12K old, perhaps periodically sticking or blocked? In my head I'm picturing (at the point of failure) coolant not getting past a closed thermostat, so the fan switch in the housing not detecting the overly hot coolant, since there is none or little to detect (hence the radiator fan not being activated).

Doubt it, but anything is possible. Low failure rate on factory thermostats here.


Also stuck/faulty thermostat contributing to coolant vaccuum system not operating properly between reservoir and radiator.

Thermostat has nothing to do with this part.
There is no "coolant vacuum system", the vacuum simply happens due to the laws of physics. You cool off a sealed container, and it will try to collapse from the vacuum inside it. Stuff a straw into it and it would suck liquid from another bottle, just like the radiator is supposed to do when it all works right.



Please let me know where my logic is faulty, if the above even makes sense. Thanks again for your time, ezone. I'll work with whatever you can give me and go from there.

YW. Did that help?

michael3n

You could always go to autozone or somewhere and get a block tester. It should tell you whether your head gasket is bad.

What does your exhaust look like?

My car had an overheating problem recently...I fixed it but easily overlooked the source at first. It turns out the end of one of the hoses was dripping...around one drop a minute. That dripping was enough to leave air in the radiator and make it overheat. Tightened the hose and replaced the cap (no more overheating). I'd definitely rub your fingers along all the hose ends and see if it gets wet. You may not see it without feeling.

jnapolitano

Yes, it did help ezone (and Michael), thanks. Enough info to try out a lot of stuff.

The car operates beautifully otherwise...almost like new. No leaks, no codes, no exhaust issues whatsoever. Uses about 1/2-1 qt. oil per 3K which is fine with me for 212K.

Last resort is block tester. My last car's HG went and I ended up getting a new (well, a 30K pull) engine shipped from Japan. Then someone flew through a stop sign and totaled it. The insurance company didn't care about the $1000 I spent on my engine.

If my HG is going on this car, I'm gonna start drinking heavily.

jnapolitano

So it turns out it is the head gasket. Thanks ezone (and Michael) for your help, it helped explain why everything was happening, and the chain reaction that was occurring because of low coolant level.

The only thing I can't figure out is why my reservoir coolant won't suck back into the radiator overnight. I tried a new OEM cap (another one), rechecked all hoses, burped car again, etc. Radiator has no problem spilling hot coolant into the reservoir, just won't suck it back up.

Would just the simple fact I have a head gasket leak that burns an ounce a day (or whatever it is) of coolant be enough to affect the vaccuum between radiator and reservoir?

Thanks again.

ezone

Yes.
The overflow recovery depends on the radiator staying completely full. If there is an air pocket in the cooling system, that increases the volume (expansion and contraction) and therefore affects the vacuum in the system as it cools.

Your combustion leakage becomes the same thing as an air pocket in the radiator. It displaces necessary liquid.


HTH