Boiling Expansion Tank!!

[OU812]

Silly Q to you pro's, but I take it that after prolonged periods 20+ mins on the motorway, if my expansion tank has boiling water in it and the cooling fan isn't running, then I have a problem with the engine's thermostat?!

Help would be greatly appreciated.

[nighthawk]

when you say BOILING, do you mean it's bubbling and spilling out, or is just f00kin hot?

also what car is it?

header tank temps are usually around the high 80's on a normal car when the cap is off, when the system is pressurised the boiling point is raised and CAN be somewhat higher.

[Pigeon]

The thermostat that switches the fan on is not the same as the engine's thermostat. It's usually in the radiator somewhere. For some reason they are usually crap and it sounds like yours has packed up.

[OU812]

It's boiling it's arse off (to coin a phrase) and the engine is very hot too - fry an egg style....

It's a 1.7 Diesel (Vauxhall Astra).

[agent006]

If you're actually moving on the motorway, as you suggest, the fan would have nothing to do with it. Sounds like your thermostat is stuck shut.

[gt5s_1985]

agent006 said:

If you're actually moving on the motorway, as you suggest, the fan would have nothing to do with it. Sounds like your thermostat is stuck shut.

Exactly. Your engine thermostat is stuck shut, which prevents coolant from flowing to the radiator. The radiator never gets hot, so the thermostat in the rad never turns the fan on.... That's my guess...

[trooper1212]

Take the car for a drive and feel the radiator afterwards, if it is cold then it is certainly your thermostat.

[OU812]

Thanks chaps.

I got the RAC on the case seing as tho I never use and abuse my membership. He reckons the gasket is on the way out which has been caused by (possibly) the thermostat not functioning.....

Sounds expensive, but cheers for the advice all the same....

[chris_n]

If the water in the rad was cold why would the water in the expansion tank be boiling, or have I missed something?

Chris

[annodomini2]

The thermostat stops the water entering the radiator, it allows the engine to warm up!

The engine needs to be warm because the oil works better at those temperatures.

[agent006]

chris_n said:

If the water in the rad was cold why would the water in the expansion tank be boiling, or have I missed something? Chris

heat rises, expansion tank at the top of the system.

Unless you drive a mk2 for fiesta, in which case your radiator will boil.