Coolant System Problem Options

[80gumdrops]

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.

[Special_Edy]

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