6G Celicas Forums

Howdy. Got a UK '96 ST202 3S-GE.

Firstly, when I start the engine I can hear air bubbles circulating around the cooling system (happens about 3 seconds from ignition).

I've checked that the coolant is fully topped up.

On two occasions I haven't heard any bubbles.. when that happens, no hot air comes in and the engine temp rises above normal. When this has happened I've felt the pipes and found that the top pipe and top of the radiator is hot and the bottom pipe and bottom of radiator is cold.

First time it happened I decided to get the thermostat replaced.

Second time, I added coolant and gave the pipes a squeeze, which must've dislodged some air, because it started working again.

Last night, I heard a few bubbles as usual and had heat as usual, but about 5 mins into the journey I gave it some welly up a hill, lost hot air and the engine started to overheat again.

After a 5 min rest, I started the engine and heard LOADS of air bubbles circulate.

Any ideas folks?

Cheers.

This is when you know the thermostat its stuck and is not letting water pass trough.

you might need to change it again, a simple test is to remove the thermostat and put it hot very hot water if it opens it meas is ok and there most be something else, also check the water pump.

Your coolant system is also air locked. Park the car with the front end uphill, turn the heat all the way up, take the radiator cap off, then start the car and let it idle. This should circulate the coolant and let all the air work its way out. I've heard that the blower fan needs to be blowing on high but I've also heard that will crack your expansion valve.

Do you have to periodically refill the coolant system? Does it overflow coolant or continuously expell air through the radiator cap with the cap removed and the engine running?

Your problem sounds like a leaking head gasket. The immense pressure inside the cylinder forces air out through the defective headgasket into the coolant system. The air has to go somewhere, so it displaces coolant through the radiator cap and into the overflow tank. A leaking head gasket can cause the endless bubbes you are talking about, these bubbles will cause the engine to overheat if it displaces too much coolant. The problem will usually get worse with time until you replace the head gasket, and eventually you may begin to see coolant in the oil(milky oil). Of course this may not be your problem at all and we wont know for certain until further diagnosis.

The lower hose is usually cold and the upper hose is hot(unless Ive got the direction of flow backwardsin my head). The upper hose expells hot coolant into the radiator so that it can be cooled, and the lower hose returns the cooled coolant back into the engine. If you run the engine for long enough, the radiator will start to heat up and the coolant flowing through the lower hose back into the engine will heat up, and the radiator fans will periodically run to keep the coolant in the lower hose below a certain temperature.
The fact that the lower hose is cool to the touch and the upper hot means that the thermostat is functioning correctly. If both hoses were warm the thermostat is stuck open, if both were cold the thermostat would be stuck shut.

I'll be waiting to hear back, but I hope Ive answered some of your questions in the meantime.

This post has been edited by Special_Edy: Jan 16, 2013 - 10:59 AM

Check your radiatorcap. If this is worn, it causes your coolant to overheat.

Radiator cap, leaking headgasket, thermostat is what Edy said. - thats what ive seen with that.

Id try replacing the rad cap and leave it idle for a while to let the air bubbles out thats the easyest option.

Then ya have replacing the termastat incase its faulty then all thats left after all that is the dearest which is the head gasket

with a radiator cap off, a good sign its a hg is when you can also the bubbles are pretty extreme and never stop. but you would already probably see a lot of exhaust smoke, mixed oil or coolant, overheating if at this point. thermostat is between what hoses are hot and cold on the lower and upper. radiator cap is the cheapest to test, borrow a good one, or see if your old gasket feels a bit thin, i just did one 2 weeks ago, and it was the radiator cap on an integra. but for your issue just check for all signs.

When I fire up the engine I've noticed that it over-revs until I can hear the bubbles move through.

Could that be a pump issue?

Also I've noticed that if I drive with the heat all the way up, it will be cold for the first 4 mins of the journey and then suddenly (like in 3 seconds) start coming through hot.

I think you have to change the water pump for starters. If you don't know the last time it was done no way to tell how old it is..
look inside the radiator and make sure it is not corroded. that could stop the coolant from flowing properly.
sqeeze the top radiator hose it it is vey solid after warming up then the pump may be good still.

as long as its not leaking, you dont need to change the water pump. its not something that just suddenly stops working. if its turning via the belt, then its moving water.

also sounds like the cooling system is full of gunk

heater should work the best when its overheatin

start by flushing the engine and heater core (under pressure-so throttle the other hose with your hand, make sure you direct water both in and out), change t-stat and rad cap,

dont bother parking up a hill, just run the motor with the heater on hot as you top it off slowly, give the hoses a few squeezes to expel bubbles, put the cap back on when the coolant level is at the top, then fill up your overflow half way and let vacuum take care of the rest. if you have to do anything else to get the bubbles out then you got other issues

That sudden switch-over isn't really a surprise if your thermostat is working well; the temperature of the water in the radiator has to hit a certain point, at which the wax in the thermostat transitions from liquid to solid and you get flow back into the engine -- and thus into the heater core. Any bubbles trapped in the heater core would prevent heat transfer from the engine to the core (and thus to the cabin air) until they were moved out by a strong enough flow of coolant.

The engine is designed to run at higher RPMs when cold.

Toyota designed the system to be self-bleeding, as long as you have a properly calibrated radiator cap and the appropriate amount of coolant in the reservoir bottle. If the overflow bottle's not properly filled the system will suck up air as it cools and the coolant condenses. What this means is that over time any bubbles should work themselves out; manual bleeding is to get the worst of the air out quickly so that you don't have to keep adding coolant to replace the volume of air removed.

usually with the water pump, you get overheating, a grinding sound, or leakage from the pump weep hole.

Okay, the top pipe is hot and under pressure, so that rules out the pump, and possibly the cap.

The main symptom is no hot air coming into the cabin at all. Sometimes a little bit will come in, and then when I drive up a hill, I just get cold air coming in.

If I remove the thermostat and it still works in boiling water, that then points to the head gasket right?

If the main symptom is that your heater core isn't producing any heat, I'd be inclined to check your heater core before I look at the head gasket. A failed head gasket's usually pretty easy to detect, courtesy of coolant in the oil (milky oil) or exhaust (white sweet steam) and a lack of coolant in the cooling system (as Edy mentioned, you'd have to refill it).

Flush the system (with a hose, don't just drain it). While you've got it apart, test your thermostat. It should start to open at 80C and be fully open (8mm) at 95C. If it's more than a few years old, get a new gasket before reinstalling. If you get a new thermostat, get a new gasket as well. Ensure the jiggle valve is correctly aligned.

Go through the proper bleeding procedure, making sure the reservoir has enough coolant in it to prevent the system sucking up air. Also make sure the HVAC dial is turned to full heat, so that the ports to the heater core are open.

Check your cooling system for bubbles. If your coolant smells like exhaust or if you have found milky colored oil or coolant in your overflow reservoir then you can be certain that your headgasket needs to be replaced.

Just had a head gasket sniff test. Head gasket is fine (phew!).

One thing I noticed though, is that I only get heat back to the cabin when the radiator is filled up directly through the cap.

That doesn't happen when I top up the coolant via the reservoir.

Blockage? Air lock?

This post has been edited by 80gumdrops: Feb 12, 2013 - 10:52 AM

you should always fill your radiator up through the cap....if you just put it in the reservoir, you're going to have a huge bubble in the system.

I had to change my radiator due to it cracking(was told it was age related). After the change I had NO heat. It took me a week to get cabin heat back. The heater core is in a location that is higher than any other part of the cooling system. It gets one mother of an air lock. It took me a week to get the air out of the heater core. Now it gives off heat better than ever.