MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

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 - Expantion tank

Hi all

I have just been for a long drive well about 60 miles and most of this was on Dual carrageways(i did stick to the speed limit I think)well when I got home i could and lifted the boot I could hear the expantion tank hissing. I took a look and the water level was right up to the top and was overflowing slightly.
first I thought oh no HGF.but I have checked the oil and there is no mayo on the dipstick and the water smells ok with no sign of HGF.

Is it just the case that the cap has failed or is there something more serious.

Martyn
M Carr

Shouldn't be getting excessively hot on that kind of run, even on a sunny day like today, so worth investigating whether there's another issue - a gunked-up or corroded radiator, perhaps?

Is it possible the level of coolant was too high? Just above the seam is the ideal. Sounds like the cap has done exactly what it's supposed to, so shouldn't need replacing.

The big question is what level the coolant drops to when cold... if it wasn't a case of too much coolant, or inadequate cooling, then the excess pressure has come from either an air/steam lock, or combustion gases.
Mike Hankin

The coolent was at between the two markers in the tank when cold and is now just above the bottom marker now so it has lost about 1cm of water.both fans are working as they should. I will check for airlocks although this is the first time I have taken it out for a run like that. the car only does 20mile a day to work and back and there has never been a problem then.
M Carr

I'm not sure whether you are suffering the same fault, but I have just bought a 2001 MGF VVC. On the drive home I kept a steady 80-90mph motorway, then the last 20 or so miles i opened it up....until i saw both the oil temp and water temp approach the red zone!!! I cruised home and almost as soon as I stopped i could hear the coolant boiling over. Engine off, didnt look like I had done the gasket in as the only leak was from the expansion tank. Being a diesel fitter mysefl i thought i should check the radiator and found masses of cooling fins missin and probably holed too although no leaks were seen. I have now a new rad on order. The fact that this only occured when thrashed is almost certainly down to the rad and I would suspect yours could be on its way out too...??#

Good Luck

Paul

A good thrashing - such as a high speed lap of the Nurburgring - does tend to make it boil BUT it is best to let the engine run on for a while when stopping to keep the coolant moving round and not boiling over in the expansion tank.

I found this out the hard way and got it in the neck from the track official for letting coolant spill on to his precious apron - fair do though as there were bikers on the track that day and the slippery coolant is not the best thing for their tyres!
Ted Newman

I have looked at the rad and there are a few fins missing at the bottom but i think not enough to make it overhheat. anyway the fan is working. Might have to take it to a garage and get them to check the combustion gases.
M Carr

It sounds to me like the expansion cap has failed. Once the cap has failed the valve will not reseat which is why you heard the cap hissing. The Halfords replacement hrc606 is a good replacement and it pays to always carry a spare.
Blue Pocket Rocket

I have ordered a new expantion cap from rimmer brothers, should be here middle of the week.
I will try halfords today but i bet this is an order part.
M Carr

Hi all

Just to let you know I managed to get a cap from Halfords today and It has worked a treat no more boiling in the expantion tank.

Thank for all your advise.
M Carr

Martyn

See my recent thread headed "Expansion Tank Cap" for an explanation of what the cap is designed to do.
John

This thread was discussed between 14/04/2007 and 16/04/2007

MG MGF Technical index

This thread is from the archives. Join the live MG MGF Technical BBS now