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MG MGF Technical - cooling (front) fan often ON

Hi all,
I have some trouble with my MG-TF 115.
After few minutes and "tourism speed" cooling fan switch ON.
I tested fan behaviour adding a led in my driver zone, wired to cooling fan relay.
I noticed fan goes ON as soon my engine has to develop a little more power... a little weak climb, an overtaking. That even if I don't go above 3000 rpm...

I suffered an HGF recently, and workshop repaired my car adding 2005 mods...

I had that problem (cooling fan) before repairing... I have tha problem now!

One month ago I went to workshop (they does "air out" purge operations) and car seemed good (I reached my home without cooling fan on). Now problem come back.

What do you think about it?

Thanks to you all.

P.S.: no coolant leak noticed.

I forgot:
oil temp: reaches 120C and stops there
cooling liquid temp: goes to middle -quite middle- of indicator range (optimal temp, I suppose). Fan goes on: temp slightly sinks and remains there.

Do you mean the fan behind the radiator or the engine bay fan ?
Jon Baker

front fan.. behind the cooling radiator; not the engine one

I would guess that there is either an air bubble near the brown temperature sensor or that the sensor needs replacing. Try bleeding the air out of the system again. Look particularly at location 'A' on Dieter's bleeding instructions:

The water temperature gauge is not a particularly reliable indicator of water temperature unfortunately - certainly the 'middle zone' covers a wide range of temperatures.

The question here is whether the operation of the radiator fan represents a problem or not. Indeed, it may just the fan's normal operation! But since you've had an HGF before, you are going to be that much more alert to problems.

If there is a problem then it may originate in a number of places:
1. The radiator - MGF radiators corrode over time and become less efficient - a problem that the TF is not immune from either, but certainly a lot less of an issue. Another problem may be silting of the radiator (could be a particular problem following a previous HGF where the oil has turned to mayonnaise, and can become a real problem to flush out). I'd check whether the radiator warms up as you'd expect and doesn't suffer any cool spots.
2. Coolant leak. Fluid can leak from rubber hoses or from the under body coolant pipes (which corrode from outside adjacent to their mounting brackets) or where the two connect. Coolant leaks will reduce the efficiency and capacity of the cooling circuit and worse, even lead to air locks where coolant no longer flows due to a trapped air bubble.
3. Another HGF. Typically, if the coolant hasn't already turned to mayo, but you are loosing coolant slowly over time (may be neglible - depends on your driving style and extent of the problem), gaskets can fail at the fire ring around the cylinder bores. This leads to exhaust gases pressurising the coolant system giving air locks, lost coolant even direct heat transfer.

Hopefully you're not dealing with (3) - but if all investigations of the above reveal nothing, then chances are there isn't a problem.

You might also want to check the water temperature sensor (mounted horizontally on the cylinder head outlet pipe - pictured here: - although failure of this tends to lead to the fan LESS likely to switch on rather than more likely.

Hope this helps
Rob Bell

I installed a "led" connected to relays to investigate fan behaviour: fan goes on "as soon as" I'm driving up a rising street. It seems as soon as engine has to develop power.

I suppose radiator runs good... if I switch off engine and I switch back on key... fan starts, then stop itself in 20-30 seconds. So I suppose radiotor runs good.

As soon as I restart engine... fan starts again... It needs 4-6 "engine on - engine off" cycles to run without fan.

Hi all,
I tested coolant liquid temperature by a cooking thermometer:
I reached my home by a 20km trip (driving at about 60 km/h)... after 10km fan goes on.
As soon as I stop my car I slowly opened expansion tank unscrewing cap...
Coolant rose (went up) and I have to screw and unscrew cap several times to avoid coolant going out from tank.
Then I put in tank my cooking thermometer and it said.... 99

It sounds like one or more things:
The thermostat is opening, but not enough, perhaps the wrong value fitted.
The waterpump is not working properly.
There is a partial blockage in the coolant system.
The radiator is not exchanging enough heat from the coolant to the outside air (maybe the fins are corroded or some waterways blocked).
Many people change the waterpump when they change the cambelt. Good luck


I think coolant system runs good:
1) I switch off engine, 20 seconds more fun on. After 20 seconds fan turn off (so radiator runs good)
2) I turn-back engine ON: after 4-5 seconds fun switch ON because new hot coolant reach thermostat (water pump runs good and no blockage are present).

I suppose engine develop too much heat. That can be possible?

Thanks again

It is more likely that your cooling system is not able to lose enough heat!

thanks to Charles.
One more question to you:
my car becomes warm (temp indicator rises to middle, about) after 2-4 km!!
I think isn't normal. Do you?

It depends on what your speed is. Mine warms up quick because its only a mile before I get on a 90km/h road.
Jon Baker

Yes even after 2 km of 45-80 km/hr mine are indicating normal operating water temperature.

Hi cnerone,

plenty of good advice here (and no bad advice!)

the behaviour you note after switching the engine off is normal ECU behaviour, it will do that whatever the temp. Without the engine running it sees little point running the fan (it does not use the sensor for the off point, only to see if it should start the cool down timer running)
Will Munns

thank you all,

@Will: I noticed "little time running" fun even if causing engine turn off without key switching (i.e.: start without rpm increase). And...
after several "little time running" fun events temperature sink:
When I switch off engine, switching on key.. fun start, then stop in 10-20 seconds. I start back on engine, fun restarts and so on... for several times... up to fun doesn't start running.
So... I suppose fun is able to make temperature go down....

Sorry for my poor english.


If you are still having a problem, there seems a similar problem and cheap solution from .org
Hope you get it sorted.

This thread was discussed between 09/04/2009 and 06/06/2009

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