MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Overheating & Thermo fan not switching on

Hi folks...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. After all the work, and replacing the ambient thermo fan switch, I still notice it doesnt come on. When I am stationary for a while after driving for half an hour or so , temp. guage starts to creep up, and radiator fluid starts bubbling away like mad into the overeflow tank, and starts to spurt its way out of the lid.
Any clues would be appreciated. Car has only done around 50,000kms and been mechanically fantastic, and well maintained. Thanks, Lawry

L Scandar

Sounds like you have no coolant circulating to the radiator. You could have air in the system which needs bleeding out (see http://www.mgf.ultimatemg.com/group2/common_problems/HGF_pages/coolant_bleed_procedure.htm courtesy of Rob Bell).

Jeff
J Lennon

Fan fuse may have blown.

Not sure about the TF, but the factory fitted 10 amp fuse in my 2002 F popped because the fan tends to draw more than that when it starts up.

Fitted a 20 amp fuse and been fine ever since.
Sam Murray

Thanks for the ideas folks..I'll be checking the above later this afternoon and report back. Any other thoughts still welcome. My hunch is its something to do with the fan's electircs, as I think it works when you remove the switch (I assume that opens the circuit??)
L Scandar

Sam, FYI the higher Amp fuses have been done already to the MGF MK2 since MGF Trophy.

Lawry,
what's up with the front radiator after when coolant *bubbles away like mad*
Is it hot ? You can check this by touching the coolant house from elow at the front.

How much did you fill the coolant to the expansiontank. It must be only till up to the centre seam. Not more.

When you have bled the system as mentioned by Jeff, then have a look to the radiator cap.
It almost dies when coolant boils over from overheating. Better get a new one in any way.

Finally I'd say unfortunately. May be your HG repair went wrong. Did you follow the instructions with checking the cylinder liner overlap versus the block ?
Dieter

Ok folks..update...took car to the mechanic who did the head gasket job a few weeks back. Looking under the car we saw signs of coooant splash, but it didnt make sense re where it could come from...I suspecte the expansion bottle leakage from the weekend had trickled its way down. We put on a new expansion bottle cap an tightened it up, so will see how that goes. Re the fan, tested ok at the relay and the switch side, so they are thinking next move is to test from there to the ECU (next week) Interestingly, they tried to connect their computer to the car, and could only read airbags, brakes etc., but not motor ....wonder if this is a clue? It has been working on previous MGTF's, so not likely to be their computer. I've yet to re-bleed the coolant..thinking that the slight leakage from a bad/ loose cap might be the culprit, but will keep a watchful eye on it. The sypmtoms of a few months back leading to replacing HG etc. are starting to gel...air-cond. not working well, coolant spurting out, overheating, fan not coming on...all at the same time, and probably all caused by whatever has caused the fan to stop &/or work VERY intermittently. Will report back again on next installment if this mystery!! Lawry
L Scandar

Both the ambient air and the radiator fans should switch on when you open circuit their respective sensors. If you try this and they both work, you can know that the wiring from sensors through ECU and wiring out to their respective fans, and their fan electrics are all working as they should.
An intermittent problem might then be pointing (either or both) to the sensors themselves or possibly to the ECU wiring loom connectors. For the latter it is well worth disconnecting them carefully and inspecting for corrosion, misalignment or damaged pins and sockets before spraying with electrical contact cleaner and reassembling and tying.
Are you switching the heater dial round to hot when you bleed the system (and checking that the wire inner cable is moving relative to the fixed outer when you do)? HTH and good luck.
Charless

This thread was discussed between 03/05/2011 and 05/05/2011

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.