Overheating
 

Well, I never really solved my earlier problem (it pretty much mysteriously fixed itself... maybe the suggestion that it was "a bad tank of gas" was right), but now I have a new, much more concerning problem.

On the way home from work today, I noticed that the temp guage was rising a little bit in slow traffic, then it went back down. Then it went back up, and it got high enough (about 85%, my gauge has no degree readings) that I decided I had better turn the heater on to cool it off. Running the heater it returned to the normal reading (50%) with minor fluctuations for the rest of the ride home.

Upon arriving home, I checked out under the hood (not that I really know what I'm looking at), and pulled out the Haynes manual. The fluid level is good, and there does not seem to be any coolant leak. The fans work (at least some of the time--I suppose they could be intermittent), and, based on the test in the Haynes manual, the thermostat is at least partially working. I'm wondering if something could be clogged inside the radiator or coolant hoses, reducing (but not quite stopping) coolant flow, or if it is possible for a thermostat to get stuck half-way (i.e. not fully open and not fully closed).

Any other suggestions? I'm totally new to this "fix your own car" stuff, and I can't afford to shotgun the problem with parts that may (or may not) fix the problem. I also can't afford to take it to a shop (although if I really have to, it will just have to go on credit, and then I can have them work on my extremely intermittent rear drum lockup).

Details: 1990 Toyota Celica ST, 1.6L 4AFE engine (shared w/Toyota Corolla and Geo/Chevy Prizm), automatic. The radiator is only about 6 mos old (not sure exactly, but it was replaced shortly before I bought the car, and the radiator looked new at the time). The hoses don't look new, but, as I said, there don't seem to be any leaks.

Sorry for the long post. Any and all help is appreciated!

well i had the same problem
dont ignore it and take care of it
i ignored the slight temp raise and blew a head gasket
cost over 500 to fix
run your radiator fan direct and if it stops the its your fan temp sensor they run around 30 bucks
it beats 500 any day
that is the number one cooling issue that cars have

Two possibilities.

A restriction in the cooling flow through the engine somewhere - clogged radiator is the most common cause for an unexpected overheat - many people don't know that you should use distilled water in your cooling system because of minerals in tap water can clog up the radiator after multiple heating/cooling cycles. So, even if your radiator isn't that old - you could have a clogging problem due to hard well water for example. Municipal city water from a lake or reservoir is not as likely to cause this problem.

A leaking head gasket that is allowing exhaust gas to escape into the coolant through the head gasket instead of through the exhaust valve like it's supposed to. You should have a problem with too much coolant in the overflow container if this is happening.

In my experience this is what happens when thermostats go bad. Usually though this results in an engine that won't reach operating temperature (because the thermostat never completely closes.)

-Jay

How do I do this? Wire the fan directly to the battery?

BTW, my car has two radiator fans, a small "push" fan on the front passenger side and a large "pull" fan on the back driver side.

I really worry about the head gasket... The overflow container is the one where you check the coolant level, right? Would I only have too much there when it is hot, or would the excess stay in the container even after it has cooled down?

Check the Haynes manual to see where your temperature gauge sender is. If it's near the radiator then the issue probably can't be a clogged system (or else why would the gauge go up, right?); if it's near the engine then it can.

Check your radiator hoses too it is possible one of them is coming apart on the inside (partially collapsed) restricting coolant flow. If the thermostat was stuck in the closed position the car would overheat within minutes of starting it. Another thing to do is straight wire the fan to the battery and drive the car and see if it gets hot. If it doesn't it is possible the cooling fan isn't cycling on and off properly. Is the coolant/water mixture approximately 50/50? It's also possible the temperature sending unit is bad, giving a false reading.?

I have absolutely no idea what the coolant mixture is. I've only had the car since March (or something like that), and I haven't done anything to the coolant (as I said, there don't seem to be any leaks, and since the radiator had just been replaced, I assumed there was fresh coolant in it).

Is it important what the coolant mixture is (given that the coolant has worked fine for several months, and just now stopped)?

The Haynes manual does mention checking the temp gauge to see if it is working, but doesn't say how to do that. However, since the car overheats when driven (it doesn't appear to if I just let it sit idling, even with the A/C on), but then the temp comes down when I run the heater (and goes back up if I turn the heater off), and also varies with driving conditions, I think the temp gauge is functioning correctly. Does that make sense?

The mixture is supposed to be 50% coolant, 50% distilled water.

The only reason I mentioned the coolant/water mixture is because of warmer weather if it was a high percentage of water and the outdoor temperature had risen several degrees recently from what it had been maybe that was having an effect. Another thing that I just thought of is the radiator cap. If it isn't holding enough pressure it would cause the car to overheat. Another thing you could do is run the car until the thermostat is open and remove the radiator cap with the car running and see if the water is circulating through the radiator good. It seems to me that it should run hot when sitting and idling more so than when being driven, because when it is being driven it is getting road draft through the radiator to help cool it.

What about all the "Never ever remove while hot!" warnings?

Check your coolant level with the engine cold, top it off if necessary.

Start the engine with the radiator cap off and let it warm up.

Look for the coolant to start moving when the temperature gets up to normal. You can also hold your hand on the top hose and feel it get hot as the coolant starts to circulate.

IMPORTANT

Look at the coolant all the time and see if there are any bubbles coming up to the radiator cap area, which would indicate a possible head gasket problem.

This is assuming you have the radiator completely full and there are no air bubbles "burping' out of the coolant when it is cold.

If the bubbles are coming up to the radiator neck when the engine is hot, look at them to see if they have any smoke or steam in the bubbles. that would indicate a head gasket.

You had the radiator replaced before. If the coolant was not properly filled (some systems need to be bled) then your problem could simply be low coolant level. Variations in temperature can be due to something as simple as the coolant level not being filled properly.

The recovery bottle should (if working properly) have a low level mark for engine cold, and a high level mark for engine hot.

If the recovery bottle is changing its level as described above, then you probably do not have an air pocket in your cooling system. In fact the best test is the recovery bottle level working the way it should.

If you have a bad hea gasket, you may be loosing coolant without any signs of a leak. Make sure the radiator is full and the recovery bottle is at its proper level. if after that you have coolant magically disappearing then the head gasket is suspect.

if you park in the same place make sure there are not leaks that are leaving anything on the ground.

regards
gary

thornburg, was the A/C on when this was happening? Was the temp gage at or near red? Have you confirmed the operation of both cooling fans?

Don't remove the cap if the car is running hot, but if the car is running at normal temperature the pressure won't be that high only about 14-16 lbs. of pressure. The pressure builds up after cutting the car off because the coolant is no longer circulating through the engine it is sitting still in the heat of the engine which makes it get hotter and build more pressure. Just use a heavy rag or towel and let it overlap the the radiator cap so nothing can spew on you and remove the cap slowly. Just open till it is loose but still locked onto the filler neck of the radiator until the pressure is off of the system. There will probably be a little bit of coolant come out, but if it is not running hot it won't be enough to amount to anything. Or if you don't feel comfortable taking the cap off while the car is running you can take the cap off and start the car and let it idle until the thermostat opens to see if it is circulating good or not. It will just take longer for the thermostat to open because the engine won't heat up as fast with the cooling system open.

Thanks for the advice, gary and Ford Man. I will try that on my lunch hour (yes, I drove the car to work this morning--that's how I know that the heater is sufficient to keep it cool, and that suggests to me that this isn't a total failure of the cooling system, but I'm no expert).


The A/C was running when I first noticed the rise in temp, but I have confirmed that problem occurs even when you don't use the A/C. I checked that both fans came on while the car was sitting idling w/the A/C running, but I haven't come up with any other way to check the fans. I may have to try the direct-wire method.

Results of the cap-open radiator test:

(Remember, I'm an engine newbie, so I don't know what "normal" is).

When I popped the cap off, the fluid was right up to the top. There was some grey-green sludge on the cap, maybe some kind of sealing grease? It did not look like corrosion or deposits. I started the car and let it run to get it up to temp, but it seemed to stop at about 45% of the gauge (normal operating temp in the past has been 50%). I don't know what I should see when it runs, but it appeared that small amounts of the fluid were going into the "overflow" tank. Very small amounts. I did not see any bubbles or steam. After several minutes at the 45% level without increase, I decided that maybe revving the engine a little bit would bring it up to temp. When I revved the engine (not real far, up to about 2000 for about 2 seconds and then up to about 2800 for about 1 second), the level in the fluid rose and it started to spill out the top. I decided that was bad and shut the engine off. The fluid sank back down. I restarted the engine to see if it was up to temp. Close, but not there. I let it idle and watched the fluid. It seemed to be the same as before, except now I saw some steam (I think) coming from the area of the cap. Not much, I really had to look close to see it. Still no bubbles. I watched the temp for another two minutes (and the very small amount of steam/water vapor) and then shut the engine off, came in here, and wrote this.

The fans did not come on during any of this. I have no idea how I would know if the thermostat opened up or not.

All help appreciated. :confused:

EDIT: Sorry for double post, but it seemed appropriate in this circumstance.

Revving the engine/water pump might have just created enough extra flow to cause it to spill out from the radiator since the top rad hose is likely next to the filler neck and the water pump would have been pumping coolant to that end of of the radiator faster than it could drain through the radiator.

It could be an intermittent problem with the fan controller or maybe an intermittent problem with the thermostat sticking closed.

As the others said, a bad head gasket will usually result in an overflowing overflow bottle and then a big air space in the radiator after it cools down (at least that's what happened to my engine when my head gasket went bad).

You might check to see that there isn't a bunch of dirt/dust built up on the front of the rad behind the AC condenser coils (shine alight through it to see how clean it is).

Start it and let it idle. Just leave it. Don't rev it or anything and leave the radiator cap on. Don't worry about it boiling over when you are doing this test as it takes way more than that to cause damage.

- If the engine temperature rises and the fans never come on, the fans are the issue(that's a given).

- If the fans come on and the engine still starts to get too hot then your thermostat is the issue unless you rev it up and see the symptom below. Usually the return line from the radiator is cold to the touch and the line to the radiator is hot.

- If the radiator is clogged, then when the fans are on and the car is getting hot you should be able to pop the revs up to 4000 or so and see the hot hose swell and the cold hose collapse(you'll definitely see this one). Since you aren't losing coolant this isn't as much of a possibility but might be still.

You aren't loosing coolant so the radiator cap is fine as is your head gasket.

Almost every car will spill water out when you rev it up with the cap off. The water pumps in cars create a lot of hydraulic pressure. It's enough to not only do that but force water past a thermostat that isn't opening to cool the engine as revs climb.

The temperature won't never get too hot with the radiator cap off as long as you keep water in the system. I have actually loosened the cap on cars before when they would run hot so I could drive them home to check them out. Be careful underneath the hood if the car is running hot. If the thermostat is stuck it could create enough pressure to bust a hose and hot coolant cover you. I had one bust on me for that reason once. I was lucky I had just pulled to the side of the road and was getting ready to pop the hood when the hose busted so I was still safely inside the car. I'm not trying to scare you I just want you to be aware.

On the Dodge Neon, I overheated once, and the problem was stupid:
the car would overheat, and I would hear bubbling, the overflow tank would go low.
Turned out the radiator cap was not sealing right, and needed to. Replaced it and all went back to normal. Couldn't tell by looking at it.

=> So it's not always a head gasket problem or a faulty thermostat

I suggest you find a forum for your car that looks technical, and search for the symptoms. It could be a known failure mode of your car. If one in a hundred cars hits it, people in the forum will know about it.

Radiator caps only cause a boil over under load. at idle they won't.

FYI on the fans, most cars are wired so the fans come on when the A/C is on, so your fans could still not be coming on due to engine temp even if they do come on with the a/c.

Can you hear the engine fan from inside the car? On many cars it is loud enough that at low speeds/stop it is audible if the windows are open.

Next time it starts getting hot, listen for the fan. If you can't hear it, turn the a/c on, but set it to the hottest setting with the blower at zero. This will limit the strain the a/c adds to the car, while kicking on the fans. If you hear the fans kick on and the temp drops either the temp sensor for the fans, the fan relay or the fan controller are borked.

As many are suggesting, current signs point to it being something related to the fans. I wanted to direct-wire the fan last night (preferably with a switch), but then I found out we had plans, and I didn't have time to do it this morning.

I don't understand have the A/C on but the blower on zero. If I turn the blower off, the A/C turns off. I can turn the A/C on and the blower on 1...

However, if it is just the fans causing the problem, and the A/C turns them on, shouldn't I be able to run the A/C at any setting? I the car never used to overheat, even with very hot outside air and heavy A/C use.

EDIT: Also, when it is very hot out, I often hear the fans of other cars running after the car has been turned off. My car has *never* done that while I owned it (which is only since spring this year). That strikes me as odd.

If after testing the fans you still have the problem you could replace both the radiator cap and the thermostat for about $10-$15 and depending on how hard the thermostat housing is to get to probably well under an hour of your time. Personally I like to change them every few years anyway as preventive maintenance and more peace of mind. That is still no guarantee I won't have a problem, but I figure it helps. I have the cooling fan on my '88 Escort straight wired to a toggle switch, because it wasn't cycling the way it should. I only have to use it when I am in town doing lots of stop and go driving.

Yes, sorry I failed to think that though. What I meant was to keep it low so the system doesn't possibly pull heat from the heater core and skew the results.

The cooling system may be marginal, and the fan problem is pushing it over the limit. I'd make sure the fans are working and/or repair them, then give the rest of the system a going over.
Have you checked the waterpump for play? Assuming it is belt driven (I don't know those motors at all) all you need to do is grab the pulley bolted to it and wiggle it, any play at all, even the tiniest amount means the pump is worn and needs replacing.

That isn't proof of a problem, some cars are wired for the fan to be able to come on that way, some aren't. I don't know how yours is wired.

Ok, here's an update for those that were chiming in on this:

After one weekend of not having time or the proper tools to work on this, plus not really believing it was the thermostat, I decided I needed to take it to a shop. I got a recommendation for a really good, honest, inexpensive shop from someone, and once I called to make an appointment, I believed them: A one week wait to get the car in the door.

They saw the car last Friday, and the guy thought it was probably a head gasket, but the pressure test came out fine. So he said the next most reasonable thing was a thermostat, and I said "go ahead and do it". (I should have told them to put in a 195 instead of stock... too late now). It turns out it was the thermostat. I wish I had had the time & tools to just give it a go, both for the experience of working on my car, and for the approximately $100 I might have saved.

A little speculation: The reason I didn't believe it was the thermostat is that it didn't fit either the symptoms for stuck open (won't warm up, or at least slow to warm up) or stuck closed (the radiator hoses should not get hot, and the car should not cool down under low-load conditions, I think). So my new theory is that the thermostat was opening and closing at the proper temp, but it was not opening as far as it should (maybe only opening a very small amount). What do you think?

Certainly sounds plausible. What is the temp rating of the stock thermostat? I also wonder if this is why American cars seem to have better working heaters than Japanese. Every American vehicle I've taken apart had a 195 in it, even my old 74 Chevy. I've never owned a Japanese vehicle.

-Jay

The wax in the thermostat could have leaked out a bit causing it to not open all the way. On smaller 4 cylinder cars though, you can still cool the engine down by running high-rpm low-load conditions. Enough water gets blown by the thermostat to cool the engine down somewhat even with the thermostat fully closed in most cases.

Headgasket? Seriously? I had a mechanic tell me that once because he'd tried 'everything' and couldn't figure out why there was so much pressure in the cooling system. I told him the cap wasn't purging and he insisted it was the headgasket and that it'd be $2500. Turns out, he put the wrong radiator cap on it and it was in-fact not purging resulting in 40+ psi in the cooling system.

After that, the engine started boiling over and he was SURE that it was the headgasket and that this was further proof of that. The thermostat needed turned 90 degrees and it has worked for the last 40k miles like that.

I don't trust mechanics.

stuck thermostat is my guess.

I agree with much of that sentiment, but this guy looked at the vehicle, and has some reason to believe it was the head gasket (as did I), but then, instead of saying "It'll be $xyz for a head gasket", he tested his theory, and charged me $50 for the test (I feel that was a little high, but lots of other shops would have charged me $100 for "diagnostics" when all they did was check for CEL/MIL codes & a quick visual inspection).

EDIT:
Jay--It is a 180 stock, IIRC. Other temps available were 160 and 195.