Coolant Problem - Sticky Thermostat?

Deke · April 12, 2008

Hi all,

Well, after 5 years my boss has finally seen the light and has given me a company car. So the GS300 has to go :(

Because I've had the company car on permanent loan for the last 2 or 3 months the GS has been sitting on the drive not being driven, which has resulted in a couple of issues. Firstly a flat Battery - no problem there, just fit a new one - but more worrying is a fault that has developed in the cooling system.

When I start it the water in the header tank bubbles ferociously as if it is overheating, although this is from a cold start. It then runs for maybe 5 or 10 minutes before cutting out, again, as if it has overheated. My neighbour took a brief look (he has a GS300 too) and speculated that it was pressurisation possibly caused by a blown head gasket. I don't think this is it as I had it to a mechanic about 500 miles ago when I sprung the rad and he categorically said the head gasket was fine.

So, any ideas? Could it be as simple as a stuck thermostat (another theory that has been mooted)? Or could the LPG be involved? Or...?

Thanks in advance.

TigerFish · April 12, 2008

Hi all,
Well, after 5 years my boss has finally seen the light and has given me a company car. So the GS300 has to go :(

Because I've had the company car on permanent loan for the last 2 or 3 months the GS has been sitting on the drive not being driven, which has resulted in a couple of issues. Firstly a flat battery - no problem there, just fit a new one - but more worrying is a fault that has developed in the cooling system.

When I start it the water in the header tank bubbles ferociously as if it is overheating, although this is from a cold start. It then runs for maybe 5 or 10 minutes before cutting out, again, as if it has overheated. My neighbour took a brief look (he has a GS300 too) and speculated that it was pressurisation possibly caused by a blown head gasket. I don't think this is it as I had it to a mechanic about 500 miles ago when I sprung the rad and he categorically said the head gasket was fine.

So, any ideas? Could it be as simple as a stuck thermostat (another theory that has been mooted)? Or could the LPG be involved? Or...?

Thanks in advance.

Can you borrow your neighbours rad cap just to check the seals are not gone in it? What does the temp guage show when it has run for 5 to 10 mins?

Deke · April 12, 2008

Temperature never gets above what I would consider to be normal. In fact, I don't even think it gets that high - I'd say about 1/4-1/3 of the way up.

There's no leakage visible at the rad cap - could this still be the cause?

TigerFish · April 12, 2008

There's no leakage visible at the rad cap - could this still be the cause?

I'm just thinking that under normal conditions, the rad cap works under pressure (maye 1 bar or similar). As the water heats and the pressure rises above that, coolant passes through the cap to the expansion tank. As the engine cools down again afterwards, the water contracts and "sucks" the water back through the cap and into the radiator. If the cap seals have gone (leaking to the expansion tank not to the outside world) then air could build up and water and air pass to the expansion tank when they shouldn't. Just a thought rather than something I have experienced. I'm not sure why that would cause the engine to cut out after 5 to 10 minutes though.

dazz32 · April 12, 2008

I would prob say it could be your thermostat....but could be wrong.

TigerFish · April 12, 2008

I would prob say it could be your thermostat....but could be wrong.

I'm dubious of it being the thermostat purely because the car cannot overheat when it has just been started from cold. The thermostat is designed to be closed when the engine is cold so even if it was stuck shut, you should only notice a problem once it is warmed up. I guess if a waterway is blocked then excess pressure could build up if the water has nowhere to go, but then I would expect the coolant to overflow out of the expansion tank. And as the neighbour said, pressure from the cylinders leaking back into the cooling system (blown head gasket) could produce the same symptoms. Is the car losing coolant? If there is a blow in the head gasket between waterways and bores, I would expect coolant to leak into the bores when the engine is switched off.