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MG MGF Technical - MGTF 120 Overheating

Hi folks...still having issues with my 2004 mgtf 120. Have had problems with the car seeming to overboil radiator fluid and overheating. Had the head gasket and thermostat replaced, but also noticed the ambient thermo fan (not sure what its called) doesnt seem to be coming on much. Have posted here before and tried lots of what people have suggested, to no avail yet!After all the work, and replacing the ambient thermo fan switch, I still notice it doesnt come on. I'm also still losing radiator fluid. Need to top up every few days., and there is a smell of fluid 'cooking' on the hot engine. When I am stationary for a while after driving for half an hour or so , temp. guage starts to creep up,until I start moving again, when it returns to normal. I notice that the engine revs seem to get a bit rougher at this point, and fan often doesnt come on. Yesterday, after about 45 minutes general driving, temp. went way up towards red, radiator fluid starts bubbling away like mad into the overeflow tank, and starts to steam and spurt its way out of the lid. Again, ambient temp. fan not coming on, even though it has previously tested as working. Odd, given that the switch was right next to the ultra hot steam emissions!!
Any clues would be appreciated. Car has only done around 50,000kms and been mechanically fantastic, and well maintained. Thanks, Lawry
L Scandar


Job 1 Replace the radiator fan fuse with a 20amp one.

Job 2 Replace the expansion tank cap.

Job 3 Thoroughly bleed the system to eradicate any air locks.

Tony Harrison


what is *ambient thermo fan* ?
The front fan at the radiator ?
Or the tiny fan in the engine bay ?

Forget the rear one but concentrate on a working front fan.
No fuse change to 20amp required at cars made after MY 2000, cause they were already standard.

OK..update...and its taken a while, but not quite resolved!

Car has now had the following done to it:
* Radiator removed cleaned out (was squeeky clean!) and refited/ bled etc. a number of times.
* cylinder head removed stripped down, cheked, replaced/ new head gasket etc.
* Replaced oli rail with uprated one
* 12v EWP80 electric water pump fitted at radiator to back up main water pump (why? Because we noticed that when idloing for long periods and car starts heating up, increasing revs a little bit almost instantly put temp. back to normal, so we assumed standard water pump struggling)
* thermostat replaced with Mackay Pressure Sensitive Thermostat kit
* whole system refilled, run up & bled etc.

NOW.....driving OK for first 50 or so kms., engine fans kicking in nicely, temp. staying in its normal position just below half. Then, driving day, about 25 kms. city speeds, car / temp guage started to creep up then kept wavering between half and almost too idle it would comtinually waver, and sometimes come down when revved. Airconditioner was on. Note: at the moment we are using water not coolant..not sure if this is a significant factor.

I am now at a total loss..we are going to try replacing the temp. sensor, as this may be at fault, as I don't imagine going up & down so rapidly is normal, or true indication of actual temp.

Again..wisodm appreciated from anyone who has ideas!!

L Scandar

See my response on the other forum

Basically check your pipe work routing which is easy to get wrong.
J Foulger

Well folks, I know its been quite some time since my last installment..but theres a reason..and still a mystery! My mechanic has had the car now since november last year! If you follow the thread, you will se we've tried replacing pretty much every part of the cooling system etc., over engineered it, brought it back to standard, etc., and the problem persists. He reckons he's eventaually dicovered that the ECY isnt sending the message to the fans at the first stage (lower temp?) so by the time it hits second stage, its too late/ too hot. Tried mirroring a second hand ECU, but it failed. Car has had all replaced bits brought back to standard I believe, and now we have sourced a NEW ECU from UK. Had this programmed locally, and apparently it still overheated. Oh..and for my troubles, I'm told the fuel pump has also now 'gone' (I reckon its due to sitting around for 9 months and seizing)I rfeckon he actually ran out of fuel. So...I am absolutely stuck between a rock and a hard place!! He's now sent it to another UK MG/Rover specialist who may have some ideas....but I would really appreciate any wisdom (other than 'get rid of it!" This MUST be able to be resolved, and I still think it must be relatively simple..what the &%%&% are we missing?? Yours in absolute frustration, Lawry!!
L Scandar

A temperature sensor, is independent of the ECU.. i.e.. it senses temperature... and the ECU decides what to do based on that.. SO.. its not hard to reason that you can bypass the ECU.. and use the temperature sensor to turn on or off, whatever you want.. You could fit your own temp sensor.. right up close to the hot water out pipe, near the engine.. and make that turn on the rad fan.. even before the hot water reached it.. but in honesty, treating a symptom doesnt treat the cause, and i would need to see that the temperature sensor actually caused the ECU to respond, before i condemned one or the other.... and it would be possible to do that independent of driving the car... i.e.. you need to make the water hot enough, and feed that round the system.. to see what happens.. so.. if i wanted to find out what was and wasnt working... thats what i would do.. and how? you need a means to heat the water to the right temp, and move it around the system.. so.. a water heater.. and a pump... is what i would put into the system.. as an add on.. then.. see what the temp sensor and ecu respond to.. Now maybe you think that is a long winded solution.. but.. you have tried everything else... and a kettle element to heat the water, and a pump to pump it.. wouldnt be that hard to put together... ?
N.J. Simon

This thread was discussed between 03/10/2011 and 25/07/2012

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