radiator fan seems to come on too often

[tv_21]

Hi I have a 2003 mgtf 1.8 which has the factory fitted prt (pressure thermostat)
I only use the car for shortish runs to the train station in morning and then back. In summer used much more, but noticed that the radiator fan seems to be on a lot.

Normally I will drive to station and after a while the car will heat up and I see the temperature guage rise, about 10 mins later I will arrive at the station. Again 8 or so hours later U get back and drive home.

It then when I was out to tesco and then came out 10 mins and began to drive home when I arrived at home and with the radio switch off I could hear the fan, i kept the engine running and could clearly hear the fan running.

I've now noticed this on a few occasions and i may be paranoid, but i would think if prt wasn't working engine wouldn't cool via radiator. I've no water loss, oil is lovely and clean. I did try and put my habd on the radiator to see if it was hot but it under the cover so only part i could get at was the radiatior bleed screw and it was cold.

Its bloomin freezing here in Belfast, so surprised the engine fan needs to come on, anyway of checking ? How easy/ hard a job to replace ? I have had car from new and has only 25,000 on clock
any advice welcome

[apttony]

It may well be that you have a poor connection on the Engine Coolant Temperature sensor.

Have a look at http://www.apttony.co.uk/Servicing/RadiatorFan.html

Simply disconnecting and reconnecting it several times may be enough to clean the connectors.

[Charless]

The one you hear most easily is the engine bay fan - but Tony's very easy test above will confirm correct operation of the radiator fan. If you know about multimeters you can check both temperature sensors once the inspection cover is off using the data from Dieter's site :-
http://www.mgfcar.de/index.htm
then scroll down the left margin to "sensoren"/sensors; the brown controls the rad fan while black/blue does the guage. The engine bay temp sensor is just above the expansion bottle in the boot and can be forced to turn on the bay fan using a hairdrier while the engine is running.

[tv_21]

Thanks everyone for the help.
I think I might just be paranoid ?
If the prt wasn't working and so the water was not then flowing through the radiator, I would assume the brown temperature sensor would switch to "open" so the fan would come on.

However this would have zero effect as the fan would be trying to cool down, an already cool radiator, so fan would just remain on, doing in fact nothing.

So surely I would then see the temperature guage begin to rise, as the engine gets hotter and hotter but isn't being cooled . Now I know the temperature guage is rubbish from reading archive stuff, but would it not rise, as what I do see is the radiator fan on and the temperature guage staeady at just below halfway.

Problem is at this stage I tend to panic and switch off the car to let it cool down as last thing I want is over heated engine.

Any thoughts ? anyone seen somethig similar ? would te temp guage rise, or is it so rubbish you possibly wouldn't see it do anything

Many thanks

Brian

[Charless]

Don't worry too much.
If you check which fan you are hearing come on, it will probably be the engine bay one. If the rad fan is coming on and off a lot it is almost certainly the brown temperature sensor gone faulty - easily replaced. But you can check both above.
The guage is OK for a slow leak/rad fan failure indication. Usually only a sudden major water loss is not detected quickly enough by the heavily damped guage response time - but steam would give you a clue in that case!