Welcome to our resource for MG Car Information.



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

Guys, advice required....

I've been offered - at the very right money - a 2001 MGF with an over heating problem..

It - apparently - starts and runs just fine, (TADTS)then overheats after "about" half an hour. and has been back to Rover for a head gasket change.. which has been done, to no avail, and now the warranty has run out...

Obviously we are more than likely looking at a new engine due to head softening et al - see Rob's post mortem thread - but obviously I want to double check all the external causal factors like fan fuse and bleeding first before I sacrifice a new engine.. and would appreciate all advice on what to look for

..which then brings me to my main question, with the darkside beckoning, will a TF135 engine go straight into a 2001 MGF? I'm thinking in terms of connectors, sensors, MEMS compatibility etc..

thanks in advance


If over heating after 1/2 hour (I presume standing still?) then I suspect one of the following:
1) the radiator is FUBR'd - they corrode after only 3-5 years, loosing fins and becoming very inefficient. Usually just before they start leaking!
2) The radiator fan has partially seized - and possibly blown the fuse.
3) The radiator fan isn't being activated because the engine water temperature sensor has failed (or its contacts corroded/dirty).

Checking the operation of the radiator fan is easy: if you've got the inspection cover removed, simply disconnect the sensor plug, and the radiator fan should come on instantly. If it doesn't then the fuse has gone.

A bit more here:
Rob Bell

Thanks for that Rob,

apparently it overheats "after a short journey" so i'd have thought that the through flow of air would be beneficial - assuming there is anything left of the rad... I guess the thermostat can't be ruled out either..


Agreed - if over heating on a short trip, it suggests that the rad is knackered, or coolant is not reaching it. I presume that the cooling system hasn't got an air lock and is properly bleed?

It is usually pretty easy to tell whether the thermostat is kept shut Mike: the pipes to and from the radiator will not warm up (both will be hot if the rad is shot). The pipes are both pretty easy to get to once you remove the black shroud trim from the front bulkhead - the pipes are under the windscreen wash resevoir.
Rob Bell

As Rob suggests, check first the cooling circuit (rad, fan, fan fuse, temp sensor, ailocks...)
A friend has got the same (?) problem (at least the same symptoms) on his 2002 TF, and it turned out to be a problem with the head. Probably a nearly invisible crack, or maybe a porous casting. Now he has a new head for 6 months, problem fixed.
Another possible cause is a cylinder liner that has moved...

Thermostat, thermostat, thermostat

but it could be a ballsed up HGF job, gas leaks into the water jacket untill presurized and then blows out of the cap - you can tell this by taking it to an MOT station and getting the coolant tank sniffed for hydrocarbons.
Will Munns

Good thinking Will!

Or of course the old favourite - the pressure cap - although I thought that was only early cars....

and thank you for the thought about the cylinder liner Fabrice...

" i have my fingers in my ears and I am not listening!!"

>> A friend has got the same (?) problem (at least the same symptoms) on his 2002 TF, and it turned out to be a problem with the head. Probably a nearly invisible crack, or maybe a porous casting. Now he has a new head for 6 months, problem fixed. <<

Good point Fabrice. It is now quite well recognised that later castings are more porous than the earlier versions. Not entirely sure when the cut point starts - but it is around 2000/2001. Your friend's problem is actually quite typical of the symptoms observed. Been a number of stories very similar to this told over on the Elise boards.

Porosity becomes more of a problem with a late casting that has been skimmed - and could be the problem in Mike's example.

In fact, this is yet another worry for my new head - insofar as its vintage is likely to be 2002/2003...

Mike, porosity is a diagnosis of exclusion. Check everything else out first - and if everything does seem to check out, then suspect the head.

I remember going to the local REME workshops as a School visit. They looked for cracks etc in cylinder heads using some dye - looked a bit like potassium permanganate? It was fluorescent... Whatever, it was a very simple way of exposing cracks and porosity that could, I guess, be used on K-series cylinder heads?
Rob Bell

Thanks guys,

am going off to see the car this evening, will report back tomorrow! - hopefully as an F owner!!

Right then...

Car duly purchased - couldn't resist!!

no mayo on dipstick, or trace or smell of leaking coolant. We took a short run of around 5 miles, the oil temp stayed low, I know I should have made a mental note, but unfortunately didn't.. got distracted trying to assess everything else.. the water temp peaked at just under halfway, So far so good! I thought, but there was a slight misfire, checked the heater, which was still blowing hot, but the engine was running on 3 cylinders under even mild load..or at least not firing sweetly..

On return, checked rad, well, the bit you can feel whilst lying on the drive in front of the car, and it was slightly warm on the o/s, and cool on the n/s.

So it's definitely lookin thermostat-ish, plan of action is to:
a) replace coolant cap - just in case
b) replace thermostat - probably because it seems the most likely culprit
c) take it from there....

Otherwise it sounds ok, no mechanical noise, and everything fine apart from the odd scratch and new zipper needed on rear window!

Oh, and the tyres... plenty of tread left on Contis on the front and P7000s on the rear...

So now back into MGF world, project time, and the call of the darkside!!

m i roberts


We've encountered overheating problems which arise when the engine speed is low, but rapidly disapppear whn the engine is revved - regardless of load. The latest to encounter this problem is our K midget - gets hot (though not so hot as to boil) driving to the track, but once out there being thrashed the temperature stays a rock solid 190 F.
Sit on the grid or at traffic lights idling - gets to 220 F. Rev it to 4000+ - it drops to 190 within seconds.

This overheating is a different animal from the more conventional type where the more load goes on the worse it gets. People someimes don't get to differentiate between the two, as who in their right mind is going to rev hell out of an engine that looks dangerously hot? Completely against instinct!

However, so long as it is full of coolant and it's not boiling, a good stab at the throttle for a 10 seconds or so to test for this won't do any harm.

This symptom appears to be a thermostat opening problem, caused by either the thermostat being faulty (have eliminated the symptoms on some engines by replacing stat) or insufficient flow in the bypass, perhaps due to a dodgy water pump.

If reving the engine doesn't cool it, it could still be a faulty thermostat (refusing to open at all), but it could also be other causes.

Paul Walbran

Thanks Paul,

I'll wait until I get it home - which should be over the weekend - before starting investigations.

I wouldn't normally buy a car with a potentially catastrophic engine problem, but couldn't say no for the money!!

I'm not sure what to think at the moment, the misfire is troubling me, but there's no mayo in the oil, no sign of steam from the exhaust, no visible scum in the coolant... so we'll see.. I've a feeling it will end up being a combination of separate faults, all combining to muddy the picture!


This thread was discussed between 11/08/2005 and 12/08/2005

MG MGF Technical index

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