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MG MGF Technical - Hot running (or not?)

I have a strange problem? that may be nothing.

A couple of times now I have been stationary in traffic(this morning) and the car temp is normal, front fan running, all of a sudden the temp guage moves towards the red very fast, I put the heater on max - no difference. I am just about to switch off when the traffic moves, I move the MG forward about a foot and the guage drops back down with a similar speed to which it climbed!!

The only thing I can think of is the water temp sender (brown one?) is starting to break down? any other suggestions anyone?

Probably unrelated but the water level in the expansion tank has a mind of its own. I check the level daily and it can be right on the line for a couple of weeks and one day it will be high, ita can stay like that for a few days and then either return to normal or be a little low (like now) but not even as low as the top up line in the tank - Very strange??

I know my rad needs changing but what with Chistmas etc I never seem to find the time or money....
kevin s

Sensor failure usually gives an incorrect 'low' reading, not a 'high' reading - so what you are seeing is a little worrying.

I wonder if you've got an air lock? It's possible if the rad is failing, and air is entering the system? Mind you if that were the case, then I'd expect the appearance of steam as the system would be depressurised.

Get this looked into Kevin - and at the very least, bleed the cooling system.
Rob Bell

does the air come out hot? an airlock would stop the water reaching the heater.

Have you checked the operation of the fans?
Will Munns

Lovely hot air from the heater all the time, front fan definately works but I haven't checked the rear fan, the engine bay light doesn't come on so I assume the engine bay is not hot enough to trigger the fan.

I recently replaced the expansion tank cap and now you can hear the pressurerelease when the cap is removed (when the engine is cold)
kevin s

A precautionary coolant bleed is easy to do Kevin - I'd do it in any case despite the lack of signs of actual leakage.

Returning to the apparent overheating - if you say that the temperature drops as soon as you get some forward speed does rather sound like a non-operating radiator fan. Blown fuse/ MEMS water temperature sensor fault. However, this is usually 'modifiable' by running the heater at full heat and the fan at full speed. That this doesn't happen is odd...?
Rob Bell

I agree it is odd, the speed the guage goes up taook me by surprise, I always keep an eye on the temp in traffic, too many old clunkers in the past!! and you could see the rate of knots the needle was travelling at! I will do a precautionary bleed this weekend and see if I rob peter to pay for the rad (TF one probably) - trouble is I want to do the under floor pipes as well, cost starts to build up!!
Kevin s

Beginning to sound like a wire has rubbed thru and is shorting out, but strange you only see it whilst stationary
Will Munns

>all of a sudden the temp guage moves towards the red very fast,

Excuse my ignorance, but I can't get which gauge you reffer to.

Assuming it is NOT the oil temp sensor, I'd say..... just forget it :)

As Will said, any wire rubbing or the sensor faulty.
The water *gauge* temp sensor is IMO the most useless gauge this car has installed.
Will be the connection, or the black coloured sensor below the more important brown coloured ECU Temp sensor.
http://www.mgfcar.de/sensor/gauge_dcp_3953.JPG
Dieter K.

I suffered from a similar problem on another type of car. One minute the header tank was filled as normal and seconds later the water would disappear only to return a minute or so later to the same level. It turned out to be an airlock caused by the cylinder head gasket leaking gas into the cooling system so check the oil and water for signs of mixing etc.. just in case.

Hope it's not

Bruce
Bruce Caldwell

>> It turned out to be an airlock caused by the cylinder head gasket leaking gas into the cooling system <<

To look for this, use an MoT 'sniffer' in the expansion tank: if there are HCs detected, then products of combustion are leaking past the head gasket fire rings into the coolant system...

A replacement head gasket is then the only solution. :o(
Rob Bell

This thread was discussed between 05/11/2004 and 08/11/2004

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