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.

[Galcobar]

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.