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MG MGF Technical - Erratic water temp

I understand the water temp gauge on the F is heavily damped, after a quick warm up my 96 has always run religiously one notch down from the middle, until about a week ago that is.
The car is now running cold and the gauge is erratic, taking longer to warm up then running anywhere between 2 notches up on the gauge, to itís Ďnormalí level.
I understand from the archive the sensors can be a problem, but I have no experience of these, or could it be thermostat or something else.
Having previously suffered HGF Iím sensitive to the cooling system, although running cold is obviously better than hot!
BTW, the levels seem ok and the heater appears to be operating normally.

Cheers, Russ.
Russ D Mellor

not hevaily damped, it lies ;-)

Sounds like you have a sticking thermostat, these tests will show you

Open the bonnet, remove the plastic cowel and you should see two pipes to the radiator, start the engine and drive a mile from cold, the gauge should just be starting to move, open the bonnet again (you did shut it before driving right?) and feel the pipes, if one is slightly warm then the thermostat is sticking.

Leave the car running on the drive - does it eventually get to normal and drop down when moving, then the thermostat is sticking

Leave the car running on the drive, wait till the fan comes on - is the gauge in the right position, if not then the sensor is duff, if so the thermostat is sticking.

Will Munns

Thanks Will, I suspected the thermostat and have bought another that I will replace during an imminent service. I remember reading on an advice page that if the thermostat had a small hole drilled in it, it reduced the thermal shock to the head of having cold water dumped to it when the stat opened.

Iím aware that this will reduce warm up time but wonder if itís a valid mod to make before fitting the new stat? If so, what size hole and where?

I will run through the other checks to ensure the problem is not elsewhere, but am reasonably convinced this is where the issue lies.

Cheers, Russ.
Russ D Mellor

I haven't done it but was quite interested until some respected posters on here last year considered on balance against doing so. The hole size was agreed at 3.5mm and top/edge orientated where it can release any air bubbles.
They also agreed that all thermostat operations were not a good idea for self control, vocabulary or any skin on your knuckles. So I have left well alone (so far) with success. I don't remember the thread title but it must still be in the archive - Good luck and do tell what you think of it.
C.R.B. Simeon

I wouldn't drill it, but i would invest in an 8mm ratchet spanner
Will Munns

LOL, the best recommendation today.

Anyway, I think the time and latest available parts have overcome the old thermostat drill-bypass idea.
(site with 3.5mm drill is at mine)
This one is ready available as spare with a jiggle valve included)

It works, of course, and I've done that too, but now we have the PRT (pressure relief thermostat) available either from Landrover or Xparts.
So why stay on old stuff.

I'd recommend to having some more investigations starting here (lots of affiliated links there)
And finally take another decision.


Thanks for your advice guys, I'm pretty sure the one I've bought already has a jiggle valve, so I won't bother with the drilling, but I will get a ratchet spanner and a flexi driver before I start the job.

The PRT does sound like a good idea, I've checked the archives on this and am probably more confused than I was to start with! For now I'll use the parts I've already bought, then look to source a PRT set up for the future. Do people normally get this new or 2nd hand? Any ideas on price?

Cheers, Russ.
Russ D Mellor

Earlier this year the possibility of a PRT kit for retro fitting was under active consideration at B&G.
C.R.B. Simeon

I had the PRT fitted to my car for quite a few years and there was definately a difference in warm up, it takes much longer.

Once warm the gauge stays level or does normally.

I seem to have an eletrical problem I assume as the gauge keeps turning off and registering no temperature. I normally find it does this when driving hard and reving for than 4000 rpm. Eventually it goes back to normal. It has been doing it for 2-3 years so have not been to bothered.

I just make sure I look in the mirrors.

Tom Randell

This thread was discussed between 26/10/2007 and 30/10/2007

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