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MG MGF Technical - Overheating!!

Hi i have a MGF 1998, i had a lambda sensor replaced recently due to emissions, the following day a hose burst on the way to work which i got replaced, the car was fine while i drove it home, it has stood for a couple of weeks since, but i used it today and found that the temp sensor was getting high (just under red before i turned it off).. I have tried running it with no cap on just in case of air lock, it is fine for a while but eventually starts pumping coolant out!! I later tried refitting the cap and running it, but i could see in the header tank that the pressure was building again which eventually started spitting coolant from under the cap and the temp gauge rising quite quickly.
Anyone have any ideas??
Thanks in advance
G Ayres

could be hgf due to a bad garage, but first you should check it has been properly blead.

Start by removing the radiator bung: Under the bonnet is a square hole with a plastic bolt in it remove bolt till green goo comes out, tighten only very slightly

Then remove the engine cover and at the rear of the engine you should find a metal pipe with an 8mm headed bolt in it, again, remove till green goo comes out.

finally replace the cap with new - never run without the cap, the coolant will boil and make airlocks and overflow.

now run the engine till hot again, check the fan runs, let cool and reblead.
Will Munns

When does the car over heat? If overheating in stationary or slow moving traffic, it could simply be that the radiator fan isn't kicking in as it should. Which if this is the case, is either due to a sticking fan (due to non-usage over the winter months) causing a blown fan, or a faulty engine temperature sensor.

More here: http://www.mgf.ultimatemg.com/group2/common_problems/HGF_pages/related_problems_overheating.htm
Rob Bell

Hi, It didnt seem to rise at first while i was driving this morining but i first noticed it while i was stationary at the petrol garage putting air int he tyres, car ticking over.. it never rises above half way usually but it did today, then when i revved it it just got hotter. i turned it off and waited for it to cool then drove it home ( about four miles at 50mph but it seemed to stay around halfway)

sorry i should have mentioned that the fan seems to be kicking in just above half way on the gauge but doesnt stop the needle rising. i have never had fan probs before and use it reguarly (just been away last three weeks)



Rob i looked at one of your links from the archives explaining how to bleed the system which i am doing now (just waiting for the engine to cool completely after the first bleed) there did seem to be air spirting out tof the bleed screws when i first opened them so am praying that this will do the job!! if not what would you recommend?

Can a failed header tank cap be causing these probs?

Thanks to both of you on your quick response.
G Ayres

In an emergency, you can turn on the heater fan to full, and set the temperature to maximum heat - it is capable of shifting a lot of heat, the cabin heater, and enough to ensure that the engine temp drops to close near normal in stationary traffic.

Been there, got the T-shirt.

Sounds to me as though your radiator fan isn't working. See above link to test its operation :o)

Regarding the coolant bleed procedure - not really that much to add. Some suggest parking the car with the nose higher than the block to try and ensure that the radiator is the highest point in the system - but I am not sure that this would necessarily work... Other than that, repeat the bleed procedure a few times over a week - eventually you should be able to get rid of nearly all the air... the rest should - if the jiggle valves aren't stuck - come out harmlessly into the expansion tank...
Rob Bell

Thanks mate i have just put it back together and given it a run round the block and so far so good... one thing i did notice was that (please forgive my lack of tech understanding on the MGF) the fan just behind the driver seat (outside the car) was working and unless im mistaken it wasnt before the bleed?? although i could have sworn there was another fan nearer the front that was coming in when it should??

How many fans other than the cabin fan is there?
G Ayres

There is a fan for the engine bay as well.
This got me at first as in front engined cars a fan only comes on in stationary traffic to put cold air over the radiator.
In my MGF the engine bay fan comes on quite a lot just to cool the engine bay I suppose!!!
I am sure someone with more knowledge will elaborate but for now there is fan for the engine bay that blows air out the vents behind the doors - I call it THE ENGINE BAY FAN!!!!
KS Gould

Up to two radiator fans (one if no airconditioning), and one engine bay fan.

Hearing it come on now is probably coincidence, and you looking out for new noises I suspect. Certainly nothing to worry about.

The engine bay fan actually sucks air INTO the engine bay, not the other way round. It's odd that sometimes it feels that it is blowing air out - but that must be something to do with turbulence? In any case, put a sheet of paper over the grille - you'll find it sucked onto the grille rather than blown away from it when the fan kicks in...
Rob Bell

In the front compartment next to the brake servo there's a fusebox that contains the fuse for the radiator-mounted fan, have you checked that it hasn't blown? I agree with Rob that the symptoms suggest that the fan isn't operating.
Mike Hankin

One other thing to check is the state of the radiator, is it blocked with debris, has half of the fins corroded away ?
Mike
mike

Hi everyone and thanks for your help... after bleeding the cooling system on Monday my problems with overheating had initially gone... as a precaution i kept checking my coolant level and found that it was going down daily, i couldnt find a leak, i have kept topping it up just in case it was something to do with air locks.. but today i noticed a puddle under the front as i left work... i squeezed the N/S front hose just behind the Rad and noticed a spray!! trouble is because of a lack of space i cant tell if it is coming from the rad or hose join.. can anyone tell me the quickest/easiest was of getting into the rad compartment to check properly?

I cant believe i have had this car a year and a half with no probs and now im getting issues with it more or less daily!!

Thanks
G Ayres

If fluid comes out when you squeeze the hose, I would suspect that there is a split in the hose to the radiator.

Unfortunately, the only way to get a good look at the rad and fixings is to remove the front bumper. Fortunately, this is easy, and even the first timer can remove and then replace the bumper within 1/2 an hour

Directions by Tim here (it's focus is on lighting, but details bumper removal): http://www.mgf.ultimatemg.com/group2/DIY/headlamp_replacement/instructions.htm

Good luck!
Rob Bell



If this radaiator is the original fitted then it is probably leaking.

If you can reach under the front of the car and feel for the the radiator fins at the lower edge any dampness, movement or crumbling of the stucture means you need a new radiator.

I have 98 F too and first rad lasted till 2001.

Also have the cooling system pressure tested .
D Brunton

Looks like I'm not the only one having fun with a rising temp gauge and subsequent sweating even more in the hot weather due to having the heater on (the wife loves that).

My question is this, do both fans come on at the same time?
My engine bay fan is running ok, quite clearly heard yet the rad fan isn't turning.
I've checked the fuses and typically all seems ok.
So do they both come on together, if so I can ignore the temp sensor and go straight to the rad. Or do they run separatly?

Ta
R Baker

Nope, the engine bay one runs depending on a sensor clamped to the bulkhead, the radiator one runs depending on a sensor in the water (by the head)

The front ones do jam, usually causing a burnt out fuse, or the relay could be dodgy - try swapping it with one for the foglights
Will Munns

Will what you doing in China??

Don't have front fogs.
Where does the relay for the radiator live?


Thou a bit more info. The rad isn't jammed. I can move it very easily by hand.

Think I'll try the water temp (brown sensor) on robs site!

Ta
R Baker

If you unplug the sensor then the fan should run even with the engine cold (engine must be running). If it fails this simple test then it isn't the sensor at fault and you can save yourself £25.

Will Munns

other questions will have to wait till I get $home - have to go eat first.
Will Munns

Will, cheers sensor kaput as you suggested!

Ta
R Baker

This thread was discussed between 19/06/2006 and 27/06/2006

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