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MG MGF Technical - MGF - Overheating


Hi,

My MGF VVC (year 1998) suffered it’s first HGF this summer. The car was repaired with the new LandRover MLS-gasket and Oil rail, new thermostat (drilled) and new water pump.

Two weeks later, on a dark evening at countryside, the expansion tank cap failed and the coolant boiled.. I stopped the engine and had the car recovered. I got the car back again from the garage after further investigation, exchange of coolant and "appropriate" bleed.

Saturday, shortly after a planned stop after a drive at motorway, temperature started to rise at high rate almost up to red.. However, I managed to get the car safely at home and at home the temperature lowered back to normal (under half).

I removed expansion tank cap next day, when the car was cold and was surprised because of high pressure in the coolant system. The level in expansion tank almost raised close to the top. The expansion bottle cap was securely screwed back before I removed the radiator bleed screw. There was no coolant at all..

My questions:

Has anyone encountered the same problem ? May the thermostat have failed, or may it not have been drilled, ? ī

I think the answer is incomplete/bad bleeding but I will be grateful for all tips

I have done almost everything that can be done incl. not rew engine over 3000 before oil temp reaches 90.

Michael
Michael

Hi, first thing that springs to my mind is a faulty expansion cap,BUT also a more serious problem like uneven height of the liners that let gasses into the coolant... Se Robīs writing on one of the drawbacks of the new ladder/ gasket combination.
Slå en signal på 0523-611032,har lite mer info/C-G.
Carl Blom


Hi Carl,

Thanks for your advice. However, I will get the car back to the garage again for further investigation.

Jag slår dig en signal senare i dag. Sannolikt efter kl 1800.


/Michael
Michael

Unfortunately, I think that Carl's right: the gasket could be leaking from around the fire rings, leading to pressurisation of the cooling system, and the problems you describe.

I fear that the head will need to come off again.
Rob Bell


Hi Rob,

Thanks for your advice.

My car is back at the garage for one or two days for further investigation. Iīll get back when I know more.

/M
Michael

Hi,

I have had similar problems in the past with my wife's car and found it to be the front radiator fan not coming on in traffic. The fuse had gone (in the fuse box under the bonnet) and when replaced eventually went again. We caught it too late the second time and the damage was done resulting in a blown head gasket and a big bill. After scouring this site we found that a mod is to replace the fan fuse (15A) with a 20A. No problems after that. If it still blows there is a fault in the fan circuitry and will need further investegation.

The symptoms were overheating, an over pressured coolant system (due to boiling) and loss of coolant.

What I'm saying is that it is a good idea to first check the fuse and replace with a 20A if blown (the ID legend in the fuse box lid indicated which fuse to check).

Hope that helps.
Phil Greenwood


Hi Phil,

Thanks for your comment. However, I got the car back at the past Wednesday and here is the news.

The garage have done compression test, exhaust test and put some "trace-liquid" (sorry, I donīt know the English name) into the coolant. They discovered a small leak at a hose-clamp. The hose clamp where also not in itīs correct position. This small leak has probably let coolant out when the system was hot, and air into when cold, which caused high pressure in the coolant system.

The compression test and exhaust test where normal and showed no signs for exhausts in the coolant.

I used the car the following days. All was normal until this afternoon. I found a small spot of coolant at the ground under the car (about a inch in size). I opened the coolant expansion cap and the coolant level instantly raised about 1,5-2 cm. I put the cap back and then started engine. There was no signs for leak of coolant.

I have also spoken to Carl Blom, and itīs probably the underfloor pipes that have corroded to much.

However, all is not bad. The gasket (Land Rover MLS-gasket) seemed to have survived both boiling, various temperatures and high pressure in the coolant system. I think its a very good gasket, but it will not solve all the problem with overheating and high pressure.

I will get back to the garage next week and ask them to exchange the hose clamps for new ones. The winter is close now, so I will not use the car any further until the spring, but I will probably have to consider to replace the underfloor pipes.

MGF is a very nice car but it is a Money Guzzler..

/Michael



Michael

Michael

I suggest you check your garage mechanic knows exactly how to bleed the MGF system. It has to be done correctly and I have found, even when the coolant is changed, it can take a few temperature cycles to get all the air out with a little topping-up of coolant until it settles down. Good luck.

Pete
Pete Tipping

I have just had work done on my coolant system, in 2 stages, 1st the rad then 2 weeks later the underfloor pipes.
Have been seeing "weird" symptoms, coolant down when car is hot then comes up. Difference can be about 1- 1.5 cm, put that down to normal pressurisation of system.
Also one day when car is cold level is a bit down, I drive car and next day when car is cold again level is up again???
I have stopped filling it up with bits of coolant so I get a true idea of what is going on.
Overall (I think)the level has gone down about 2mm from where I started from, to the highest level it shows.
It has had a pressure test and test for carbon monoxide in the coolant. Both ok.
I am off to Halfords in a minute to order in another expansion tank cap, the one I have on it is only a couple of months old but I may have over tightened it a few times.
Could all this just be the system settling down after the work done - air locked in system finds its way out to expansion tank and level came down -this did occur to me and then I saw Pete Tipping's post?
Maybe I am clutching at straws here?!
KS Gould


Hi,

I would not worry to much if the level in the expansion tank differ some cm from one day to another, but itīs another thing if the level constantly is going down over a period, or if the level suddenly is going up about 2 cm or more when the expansion cap is removed.

However, I am not an specialist about cars and their coolant system, but I think itīs important to ask the following before inspection of the coolant level:

-The use of the car from one day to another: (city or country/motorway) and time.
-How often the car is used.
-Parking place overnight (outside or heated garage) and temperature differences.
-Summer/Autumn/Winter..

I got my own MGF back from the garage in this week. The garage has changed some hose clips under the car and bleed the system. I will use the car as much as possible before winter and carefully watch the coolant level. I consider to take the car to another garage next spring for another check (thanks to Pete).
Itīs worth to consider, because the garage I use today, has about 15 employes and a lot of different cars (incl MG). The garage that I plan to visit is operated only by the owner himself and has only MG, Rover and Alfa Romeo. The "one-man" garage will probably know the MGF better than the "15-man garage"..

Michael





Michael

ks Gould ..if the tank cap is the same as the one i got from halfrauds a while back...it fits as in screws on but is to tall to close the metaL ENGINE BAY COVER.
KEEP YOUR RECIEPT i wish i had :0))))
Mel..
m e johnson

Hi,I just wonder sometimes ,are mechanic,s completing the bleed process with the heater knob in the correct position, which is full on. This would explain to me anyway a fluctuating water level for a while or an early HGF. Providing the correct cap is used "white dot center" some of the excess air pressure may bleed off in time, if not, its an invitation for an air lock from the heater trying to purge itself.All the care in the world wont make any difference if the heater wasnt on during the drain and bleeding.I think one could get away with it with a normal engine but not it seem,s with the K-series.Cheer,s Bob
rb wadwsorth

My expansion tank cap is from Halfords, it is not the same as the one I had before or the one that came with the B&G LLW kit which I was using before I got the Halfords one. The Halfords one is by a company called "Frontline" I think but then that may be the stuff I put on the cat to rid it of fleas!!! Could have been "Firstline" perhaps, the company does rad caps for lots of cars, I looked online when I got the cap.
It IS bigger and chunkier than the B&G one but still fits under the flap. I like it because it looks more substantial than the other but I don't know it it is any good or not!!!
I think the level is ok, am still keeping an eye on it.
Don't think the general trend is down, yesterday the level was to an arrow I had drawn on the tank and filled to 2 weeks ago. Not put any in since to see what is going on as it gets confusing when you put in bits of coolant here and there!
Thanks for the advice everyone.
Kate
KS Gould

Presumably no relation of Frontline Spridget then...
Rob Bell

It was mentioned above that the rad cap may have been overtightened. I think this is pretty unlikely and it was recommended to me by an 'MGF' trained mechanic to get it really tight - by hand of course!

I have just broken into my old one which had failed a pressure test on the annual service. I saw this actually retested and the cap would not hold the pressure and just leaked away. The seals all looked perfect and there was no corrosion. I reckon these things fail due to muck getting in between the little seal and seating which allows air back in when the system cools down.

The cap itself I found to be very substantial and made of a very tough plastic material.

I recommend getting any new cap tested at the time of purchase. That way you know its right before you start. Carrying a spare is no financial hardship and fits nicely in that central bracket in the boot...

Pete
Pete Tipping


Hi Pete,

Thanks for your advice. However, I got a new cap for the expansion tank, but I am not sure that it is a correct one. The cap is blue and is marked at the top with the following: MIA A878, 1.4 Bar.

I think that the cap is a strong one, but 1.4 bar appears to be very heavy. Is this normal ?

The car and itīs coolant system appears know to be normal after the last visit at the garage (where they changed som hose-clamps under the car). The coolant differ a little from one day to another, but not more than a cm. No trend downwards and no signs for leak.

Another question for the one who knows: The oil temp gauge has a mark at 60 degrees and a mark at 120 degress and so on.. But what about the mark between 60 and 120 degress ? Is that 90 or 85 degrees or something else..? I thought it was 90, but I am not sure..

Michael
Michael

This thread was discussed between 23/10/2006 and 30/11/2006

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