Over Heating/Under Heating/Hot Air from Blower then Cold Air

[jigsaw]

Have a mysterious problem!

When I drive my car it is heating up fairly quickly - usually I have to sit shivering for 5-10 minutes till heat starts coming out and then its nice and toasty! Temp Gauge never goes above the half way point and I have a Kenlow fan (fitted 4 years ago).

Last week I was driving along the M25, not a problem at all, and then when I came off and stopped at traffic lights, after a short time the hot air from the blower started coming out cold - and I noticed the temperature gauge going up on my dash close to the red! When I pulled away the temperature gauge went back down and hot air started blowing out again!

I have had no issues with the car for a while now, nothing replaced recently that would have caused this, there is no mayo in the expansion tank, filler cap or dip stick and even with the problem the temperature gauge has not gone quite into the red - and there has never been any steam coming from under the bonnet!

Anyone got any ideas!?

[kam-325i]

If its a M20 engine, Either water pump has gone or air lock in heater matrix

99% it will water pump failure.

[blingsta]

sounds like viscous !!! as the temp starting going back down when you started moving again..

[kam-325i]

But the heater drops to cool air when idling, not enough water circulating around the system.

[Brianmoooore]

Won't be the viscous coupling. The heater would get hotter than normal when the temp. goes up, not lower.
It could be a water pump rotor failure, But, being a pessimist, it could well be an air lock near the back of the head, that clears when the water flow is high enough. The probable reason for this recurring airlock would be a failing head gasket.

[jigsaw]

Thanks for the input so far, I have a Kenlow fan fitted as I mentioned on the car so it cant be the viscous fan as there isnt one!

Thanks for the advice Brianmoooore - I am an optimist to I will be counting my chickens and hope that it is not the head gasket and will go down the route of the water pump and other suggestions and let you know how I get on!

There is no mayo anywhere either way round but will get it pressure tested...

[johnl320]

Could you get the air in the header tank 'sniff tested' for exhaust gases I have heard of people getting it done to confirm head gasket failure.

[johnl320]

like this
http://www.ebay.co.uk/itm/BLOCK-TESTER- ... 25698a34f3