What causes an engine to overheat?.

[Ben]

Don't say heat.

Here's the scenario.

For around 2 years had a coolant leak on my 1991 16v Golf. Leak turned out to be from the head gasket. In this time all I had to do was check the coolant before every journey and top it up. Never had any issue with overheating.

So. 200 miles ago had the engine stripped and checked. No internal damage so went ahead and had a new head gasket fitted along with the rocker cover gasket etc. New cambelt and tensioner, engine mounts etc. About 12 months ago fitted a new radiator also.

Car was running perfectly so sold it on to my sisters boyfriend.

Two days into ownership and the car started to overheat in traffic with steam coming out of the coolant bottle overflow. Fan was operating normally and the engine temp began to rise, then something popped and the coolant was dumped onto the road.

So the question. If the fan is operating and there is coolant in the system. Why would it overheat ? ..... what actually happens to make a car overheat.

Any and all suggestions greatly appreciated.

[Econ]

Check the pipe work could be some kind of blockage that is stopping the coolant geting around the engine also check that the pipe work is soft if its hard might be worth replacing. Its probably not the cause but its worth checking

[Ben]

I've told matt (my sisters boyfriend) to have it pressure tested tomorrow. Along with a radiator flush (I was wondering if there may have been a mayo buildup in the rad).

I've replaced the top hoses but admit I've never checked the bottom hose so fingers crossed it's that.

[Nik]

Could check the thermostat to make sure it is opening.

Is the heater working?

I would say that a blockage does sound like the most probable cause from what you have described.

[sdminus]

Sounds like the stat to me

Scott

[Ben]

interestingly after pumping him for more info - he opened the coolant bottle whilst it was hot - guessing he may have caused an airlock.

Going to have the stat changed tomorrow.

[Econ]

If it was the Stat would the fan even start up?

[Gerry H]

If it was the Stat would the fan even start up?

Yes! The fans operate from the temp. sensor mounted in the head or block. The thermostst not opening is essentially a blockage to the rad. Normally, the water circulates around the engine and heater until the stat opens to utilise the rad. cooling.

Edited to say, that's cr@p! The fan thermostat could be in the rad :oops:

[duncan]

I little trick I used to do on the mini was remove the stat and effectively make it run an open system all the time - may be possible to do that to test whether the stat is causing the problem ??

[Ben]

ahh but this is a Golf ... the golf set up seems a wee bit different.

Either way it's in the garage now and we'll see what they say.