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.

[80gumdrops]

Nailed it. It was an air lock somewhere by the heater core.

Parked car on incline, turned heat on full and removed radiator cap.
Gave the pipes a bit of a squeeze and then topped the radiator up to the brim with Toyota coolant.
Gave pipes a few more small squeezes which shifted a few bubbles.
Got in car and waited for thermostat to open.
At first the engine temp was rising again for about 6 seconds and then I heard it.. loads of air shifted through the heater core (finally).
Engine temp dropped immediately and I had heat back in the car at the same time.
I then switched the engine off and repeated the process to account for the air displaced by the burp.

Thanks dudes!