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MG MGB Technical - Mgb running hot

Hi, I have a 1978 MGB GT which keeps swithching the radiator fan on after about 3-5 minutes in traffic and the engine starts to miss fire a bit. I have replaced the head gasket, had the head checked, thermostat replaced,water pump OK, checked the timing. The only thing I have not replaced is the radiator (I have flushed it) it seems OK. Any ideas before I change the radiator.
P Hobson

When the fan comes on does it cool the engine and cut off? It's normal for fans to come on in traffic. If the fan cools the engine after running a few minutes and cycles off the engine isn't overheating. If it is really overheating I doubt that is the cause of the miss fireing

I would look for an electrical problem. Check the battery voltage with a voltmeter at the brown wires on the fuse box with the engine running and the fans off. It should be around 13.5 volts. Is there a big change in voltage when the fan comes on? Does your car have electronic ignition or points?

Clifton

Clifton Gordon

Thanks clifton

I think I might have found the source of the missfire, there is a small hairline crack in the distributor cap. As for the running hot issue, the fan does cut in but seems to take an age to cool the car down and swithch off. I thougt it might be a silted up radator but I am not sure, because when you feel the rad when the car is hot there are no cool spots.

Pete
P Hobson

Pete,

As Clifton says it is correct for your fan to come on after a short wait in traffic or slow moving traffic.

The fan will probably run for longer than the fan on a modern, but not airconditioned, car. This is because the fans on modern cars tend to be larger and they are cowelled, which makes them more efficient at moving the air through the radiator. The uncoweled fan on a 'B looses air sideways. So it does as much stirring as pushing.

As I have seen other people say on this site before, if you have not got steam coming up round the bonnet then you are not overheating.

David
David Witham

In the morning, start your car, let it idle to operating temperature, turn off car, feel radiator for cold spots. Cold spots are indicative of a clogged radiator.
Kimberly

This thread was discussed on 11/07/2006

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