over heating on M20 B25

Wed Jul 21, 2010 10:13 am

Hi, hope some one can help.
Got stuck in a bit of traffic yesterday, thanks to all the rain.
I have recently fitted a new radiator, water pump, timing belt & tensioner & v belts, so can't understand the over heating.

The needle went into the red, and just at that moment, the traffic started moving again and I managed to cool it down again once I was moving, but not a good feeling though watching the needle getting higher and higher.

I've never been stuck in traffic for that long before, so I don't know if the problem has always been there.

Any suggestions.

Wed Jul 21, 2010 11:13 am

Yep, sounds like you have an airlock. You will have to bleed the system, open up your heater when doing it.

Wed Jul 21, 2010 3:16 pm

Yep, sounds like a good bleed of the system may be in order. Its not uncommon to have to repeat the procedure several times to expel all the air from it. Make sure heater is on hot setting.
If that doesn't sort it, your viscous fan might be on the way out.

Orrr, could be the head gasket..........

Wed Jul 21, 2010 8:48 pm

If the heater is working properly, it won't be an airlock. The first thing you should have done when the needle climbed was to turn it full on.
Most likely culprit is the viscous coupling between the water pump and the fan. If you rev the engine when it is overheating, the coupling should be locked, and the fan will roar.

Wed Jul 21, 2010 10:35 pm

i agree with brian. sounds like viscous not locking, especially as the temp went back down when you started moving again. The ultimate test will be the rolled up newspaper jobbie !!!
let the engine tick over, and if it starts going over halfway, touch the fan with the rolled up newspaper.. the fan shouldnt stop and should shred the paper up