Rising temp guage

[Simon Mulley]

I know this sounds odd but when I drive over 50ish and its raining hard the temp guage goes sky high,if I slow right down to 30 it goes down!!! Help,it doesn't do it when it's not raining,anyone got any ideas,it's driving me nuts.

[Conker]

Weird. Could road spray be reaching the sensor wiring on the side of the head?

[Lap]

Could the water pump belt be slipping because of the rain kicked up? Does the heating go colder at the same time as the temp gauge goes sky high? 

[Conker]

...Does the heating go colder at the same time as the temp gauge goes sky high? 

Thats bloody good thinking Batman!

[Simon Mulley]

I can't say I've noticed,I'll check next time it rains.It gets worse because since it happened the car is using between 1/2 and a whole litre of water a day but I can't see any leaks so I'm assuming the head gasket might have gone.I rang AMD in Thurrock and they want 480 quid to do it !!!!! I nearly had a heartattack.I'll have to take it to a garage to check if it has gone.

[Conker]

Ah, I think that maybe the rain thing might be a coincidence (afterall, it does rain here a lot doesn't it!).

When you run low on coolant (e.g. due to a leak or headgasket failure) your heater will go cold as eventually theres not enough coolant in the system to reach the matrix.

At this time of year its really hard to check for leaks as everywhere is always wet, so I would drive it to a multistory car park or something like that and park on a dry bit of tarmac. Remember that some leaks won't be visible as the drips may be evaporating immediately e.g. if they are landing on the engine.

When my headgasket went I had the same symptoms as you describe but the steam coming out the exhaust was clearly visible. Don't get confused with the normal steam coming out of a cold exhaust though - the steam symptom only applies when the engine and exhaust is hot!
Really you should get a compression test done sooner rather than later.