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MG MGF Technical - Coolant level rise


This may be bad news for me, but I'd like informed confirmation.

What does it mean if your coolant level actually rises and does not fall?

Regular check of water level was done when the car was still slightly warm. Bit of a hiss is normal here. Level seemed ok, but rose slightly. Odd.
Worried, I checked again later - again while still slightly warm. The level rose further - about 1".
Since then it hasn't gone down.

Water and oil temp gauges have been fine. Not been brave enough to test the rad fan by running the car for 20 min stationary yet! Maybe I'm inventing things, but the air temperature from the vents seems hotter than usual(!).

Finally, the car is already booked in for a testbook appt as I think there's a sensor problem somewhere as idle has been a little high. I'd assumed temp sensor, MAP sensor etc. but wanted confirmation.

Are they linked...?

...or do we think that I've got combustion gasses in my water and am gonna get a lovely HGF?

Answers on a postcard/sympathy letter/fiver for the fund/etc.... :o)

P.
Paul Nothard

The apparent rise of coolant might not be anything sinister Paul, but there is no harm in getting an exhaust gas 'sniffer' and checking out whether there are detectable hydrocarbons in the expansion tank.

The high idle could easily be the ECU temperature sender - I know that my car has gone through 3 in 9 years... Other causes, as you know, include dodgy IACVs etc ( http://www.mgf.ultimatemg.com/group2/Throttle_body/index.htm#problem )
Rob Bell


Shall do that... but I'm a tad concerned and confused why the water could rise. I cannot find any rational explaination... and I don't like that!! :-(

Idle valve is ok. Have checked that.
Will get access to temp sender tonight... if the car gets me home!! :o)

Booked into the Lotus friendly garage that I used before... so we'll see what happens.

P.
Paul Nothard

Check the jiggle valve in the cylinder head (RH rear side of the engine). Disconnect the hose from the expansion bottle an blow through it with your mouth to make sure it is open. It is essential to keep it open or else air may build up in the head's water jacket causing overheating and eventual HGF.
Jon

Thanks Jon. Will try that this weekend.

P.
Paul Nothard


Jiggle valve fine. Had a good look about too.

Now convinced that the head gasket is going. :-(

Stopped driving it and will get it pressure tested and fixed as appropriate. Thinking about <shock horror> selling the car anyway so I want the rather nice head that's on it preserved for the future owner.

(If anyone is looking for a well used but well cared for fast VVC then there'll be a bargain to be had soon!)

P.
Paul Nothard

Paul, you can't be turning all sensible on us can you???
Rob Bell


Who said sensible? ;o)

Nothing decided yet... but I doubt it'll be too sensible.
Paul Nothard

Hi Paul - where this hiss coming from?
Do you mean the level rose after you took off the filler cap?

That would release ~ 15 llbs pressure if hot, make more than a 'bit of a hiss', and certinly lead to expansion and a rise in level.

jt


>>Regular check of water level was done when the car was still slightly warm. Bit of a hiss is normal here. Level seemed ok, but rose slightly. Odd.
Worried, I checked again later - again while still slightly warm. The level rose further - about 1".
Since then it hasn't gone down
John Thomas

Coolant level will rise in the tank if the cap is a bit duff. I had this a couple of years ago and a 3 quid cap solved the problem.

Tim
tim woolcott

>>
Who said sensible? ;o)
Nothing decided yet... but I doubt it'll be too sensible.
<<

Well, it has got the Griffin badge on it! ;o) ;o)
Rob Bell

Hi John, all...

The hiss was coming from the cap after a motorway journey. Engine was very hot - obviously. Seemed that the coolant was under unusually high pressure tho. The level of the water had risen slightly. I did not take the cap off at all at this point!! :-)

Let it cool. Still a little warm, but the pressure was still high enough with the level rising about an inch more when I took the cap off. This could be down to it being warm... but the level did not drop back down overnight on a cold-ish night. :-(
Caps are cheap so I replaced it the next morning anyway.

Similar happened the next day with the level rising a little more. This was checked when cold. Not good. :-(

Next day the pressue obviously got too great at one point and the (new) cap started releasing presure - steam. :-(

It hadn't lost all its water as I caught it quickly.
Haven't driven the car since. Now that it's topped up it does turn over and sounds fine at idle but misfires on one cylinder for the first 30 seconds. Coolant seeping into cylinder overnight? Dunno.

I'm pretty sure it's the very early stages of a fire-ring HGF. Just glad I think I've caught it early. :-)

P.

ps. Quite separate from this problem, we had decided to sell the car <sob> - see other thread for a bargain!! The new car is blue, tupperware and does indeed have the Griffin badge!
Paul Nothard

This thread was discussed between 09/03/2005 and 25/03/2005

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