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MG MGF Technical - I'm in hot water!

You have no doubt seen my recent problems on this site. Head gasket replaced at 66,000 miles. More
recently inlet manifold replaced, along with the
piping at 85,000 miles.

Everything lovely. Went on holiday to Scotland for
a week, had a great time with the top down every day,
did 1357 miles return - no problems at all, loved the
car. Now done 86,500 miles.

The last 20 miles to home, temperature guage rises
steadily before I stop just before it reaches the
top. Take a break for coffee, fill her up with
half pint of water. Drive on home. Temp guage again
starts to rise, but I make it home. After 3 hours
I drive down to Bedford to swap cars with my son.
Temp guage never rises above half way, even on fast
motorway driving.

My son phones me up today. Has encountered the same
problems on his drive to South Wales. Had to stop
3 times to let engine cool down, top her up, etc., but
eventually he made it to Swansea. Comes back on

Any ideas what could be happening and how to cure it
will be appreciated.


Bill Pearson
W.A. Pearson

Hi Bill,
Sounds like you've got a leak somewhere and have also now got air in the system. When you say you have to top up the coolant - has it fallen below the mark half way down at the seam level. Worth changing your pressure cap as it may have gone duff and also having your system pressure checked for leaks, if you cannot see any obvious signs.
W A Nixson


Thanks for your comments. I just hope my son can
nurse the car back to me on Sunday. I did have
the pressure cap replaced when it failed about 1 year ago. I don't know how long they last, but I have
asked my son to get it checked by a garage in Swansea
if he can on Saturday.

The level of coolant had fallen just below the
projecting plastic marker which I then filled the
system to cover it. Can't recollect if the coolant
had fallen below the mark at seem level, but will
obviously check these things out from Monday onwards.


W.A. Pearson

How old is your radiator, Bill?

Hi! Charles,

Probably 2001 when the car was made. I have not
replaced it in my ownership.

No sign of leaks anywhere. The car was losing water
prior to this when the plastic inlet manifold was found to be the cause and recently replaced and I thought the problem was solved.


W.A. Pearson

I was thinking a slow and variable leak allowing small amounts of air back into the system which might explain the high temp reading - losing a half pint does not.
If some tubes are a bit denuded of fins and internally occasionally block with debris the temperature and pressure both rise forcing a weak point to seep. This can dry before it drips, even when parked up, although if you have the rad out for inspection it leaves evidence.
If you have the rad out you might just as well replace it, although I hate the idea of gratuitously changing working parts.
Re bleeding sounds a good idea if you haven't already done so. I am not convinced about the expansion cap blame, as at least one regular poster here has had the same one from new for 12 years without issues. I suspect they may get blamed for a lot of unexplained events. I was losing small, manageable amounts on and off for two years when trusted local garage having checked all the usual suspects (incl plastic inlet manifold!) decided on unipart's version of radweld which has so far prevented any further loss.
However my temp guage had never risen above normal - even in sweltering mediterranean two hour stationary/crawling traffic.
Good luck and do tell us when it is finally traced.


Well my son nursed my car home from South Wales
on Sunday. Phoned occassionally to say that the
temp.guage remained at the half way point, but that
the yellow (engine block) light remained on. Told
him to continue whilst listening for any change
in engine tone or increase in water temp.

Started the car today, (Monday). Seemed ok. Engine
sounded ok, yellow light still on. Maybe an electrical
fault? After a few miles, the cooling fan engaged (might be a clue!, but engine temp remained constant
at the half way point. Cooling fan often comes on
after short journeys, is this normaal?

Any help would be appreciated before I go back to my
MG mechanic (who is recommended by MG car club etc.)
but after 3 years of ownership, getting rather fed
up paying out for a new head gasket, inlet manifold
etc., which has cost me about 2,000 apart from the
normal servicing, runing costs, replacing tyres,
break pads, etc., without any end in sight!!!! Do I
cut my losses and buy a Honda S2000. I already own
a 1995 Eunos Roadster (inherited from my late wife)
and 13 years on, is not a pain in my pocket - sales
through MOT's and is serviced at the required intervals.


From a pretty peed off Bill
W.A. Pearson

Hi Bill,
When you say the yellow light is on -what symbol is it showing. The engine bay overheat symbol is red on my '96 F. It has an engine outline and thermometer symbol - rhs above the abs light. It could be a failure of the engine cooling fan. Does this run or are you talking of the fan on the radiator?
aka willyphixitt
W A Nixson


The light that stays on is the yellow one with the
outline of an engine on it. The cooling fan nearest the engine bay comes on more often than I would have
thought necessary, even on short runs of 5 to 10 miles.

Someone else said if that light stays on it could be
something to do with emissions, i.e. oxygen sensors, another that it could be a fault in the inlet manifold pressure sensor (which one is that and where
is it located?) That is the other problem, sometimes
when you come to a stop, the engine dies. Re-starts
ok, but then dies again. Tried the trusted method
of resetting the ecu by depressing the accelerator,
which seems to do the trick for a while, then the
problem re-curs.

I'm booked in for the MG club Isle of Wight weekend
in September, so I would like to think that I/we have cracked the problem by then.


W.A. Pearson

Hi Bill,
The MAP sensor (manifold absolute pressure) is located near the o/s. It is forward and to the left of the oil dipstick. The fuel pressure regulator is immediately in front of the dipstick. Other sensors to check are the engine coolant sensor and the intake air temperature sensor (IAT). The IAT is on the rear of the motor just below the oil filler cap on top of the engine. There is an ambient air temperature sensor just forward of the dipstick and to its right (o/s).
Hope one of these is where your problem lies.
Good luck.
willyphixitt (I hope he does)
W A Nixson

Had a similar problem many years ago. Dealership had it four times with 4 different "fixes" before old bloke in workshop spotted one side of coolant pipe hot, the other cold. Turned out to be a sticky thermostatic valve telling the ECU that the car was constantly cold. Thus overheat only happened at slow speeds, high speed keeping engine cool with airflow.
Just a thought.
C Millar

Thermostat malfunction is not uncommon as it is actuated by the bypass and the flow through that is only just enough (that is one reason why it's all so sensitive to air in the system).

We've had engines in which this is readily discernable - they get hot at slow engine speeds and go back to normal with a few revs on. Check for this by increasing engine speed to around 4000 RPM (doesn't need to be under load) and seeing if the temp starts to drop back (it will be reasonably fast in responding if this is the problem).

It's not the only way thermostat problems manifest themself, but as mentioned above the dead give-away is the cool pipes to the radiator even though the engine is hot.

Paul Walbran

Hi mate
Had a very similar problem to my 98 mgf was loosing water when i bought it thought nothing of it till i checked in here. Was told to get it checked out .Turned out to be the water pump was leaking so didnt leak until water heated so didnt notice any leak anywhere .So got it replaced and problem solved got it all done for around 150 .Hope this is of help to you .

This thread was discussed between 01/08/2008 and 14/08/2008

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