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MG MGF Technical - Coolinh system problems

A few days ago we did a 25 mile drive to Cambridge and sat with the engine idling, after about 5 minutes i noticed the rad fan had come on, unusual considering how cold it was outside, and the temp gauge did not go up. I thought nothing of it until today.

Started the car up and let it warm up (bad idea i know but it was cold) After 15 minutes i noticed the rad fan on :S

This time the gauge had gone up above the middle, something i had not seen even in the summer months, also the expansion tank was bubbling...

Now, for the next bit of strangeness, the rad was stone cold so nothing but cold air was blowing.

The heater was warm but not blowing its usual heatwave. I decided to take the car for a drive and it was all normal, heater got hotter, fan didnt come on, temp gauge stayed normal, a notch below the middle.

I returned home and checked all the levels, water had dropped from earlier, oil was fine with the exception of a tiny blob of emulsified oil at the bottom and dribs and drabs along its length, most likely condensation from its 16 mile daily trip to and from work. Nothing on the two oil caps either, and the coolant itself is perfectly clean and doesnt smell like combustion pressure fumes.

So what am i potentially looking at here? Dont want to tempt fate and say its HGF as there are not enough signs to convince me. Thermostat not opening fully? Air lock in the system? Blocked rad?

Running the heater on full blast seems to keep everything under control in most normal driving circumstances but i obviously want to ensure i catch the problem early.
Gareth Kidman

First change the coolant cap, then consider the thermostat.

But bleed the system now!
Will Munns

"most likely condensation from its 16 mile daily trip to and from work"

I would think this is more than enough each day to avoid any condesation problems - it is usually a mile or 2 each day that prevents the engine getting up to sufficient temp to evaporate any crankcase water vapour :(
Tony

It usually does 7-8 miles each way to work and in this time the oil temp gauge barely moves so although the coolant is getting hot, the engine isnt fully up to temp IMO. Being winter really doesnt help.

Anyway i've bled the system out, there didnt seem to be much air coming out, but initially coolant coming out was stone cold.

Took it for another drive, and the heater this time was definatly hotter, it usually gets too much but it really does cook now, temp gauge solid as it usually is, and when i got back i checked the coolant pipes at the front and the rad and this time they were warm!

So maybe it was just an airlock, god knows how as i never touch the system except the level. I still have suspicions that it could be loose fan belt or failed thermostat so both of these will be checked ASAP.
Gareth Kidman

you can get an airlock by localized coolant boiling due to a faulty cap, hence the "replace the cap" comment. as soon as you get boiling then the effect starts to snowball
Will Munns

Well i reckon it's HGF... Took it to Cambridge again tonight and seemed fine until we stopped in traffic and i noticed the fan on again.

Temp gauge had not gone up at this point. We stopped for something to eat and came back after 15 mins. Let it idle for about 10 mins, fan came on again, rad cool, and this time the gauge went up.

So we rushed home and literally as we went up the drive the temp gauge shot up, steam pouring out the baxk and the heater output went cold :(

No water left in expansion tank. Bugger. It may well be we have caught it early as there is still no signs of water and oil/vice versa mixing so unless anyone has any great ideas or theories the head is coming off for a new HG, metal dowels, therrmostat, maybe a water pump, belts etc..

Gareth
Gareth Kidman

Any more thoughts people? I topped it up the following day, bled it out and it was fine... I have purchased a new expansion tank cap and hope its just that.
Gareth

>Well i reckon it's HGF...

From your brief inspections and descriptions, I fear you are right.

>after about 5 minutes i noticed the rad fan had come on,

The engine will take much more then half an hour under current ambient temperatures to get the front fan coming off.

Did you check the coolant non-return valve (jiggle valve) in the inlet manifold for blockage ??
http://www.mgfcar.de/bleed/3817engine_left_l_1.jpg

seen from inside:
http://www.mgfcar.de/inlet_manifold/DSC01737.jpg

Not sure but might be an option beside of what Will said with the thermostat.

- loosen hose clamp
- swap on another fitting hose (catch coolant while spapping the hose)
- strong blow some air in to remove derivates or whatever.
- swap hoses back and clamp back.
- bleed again and test

HTH
Dieter
Dieter

The fact that your radiator was stone cold at one stage must indicate that the thermostat was sticking. I had this problem with my old '97 VVC where the 'stat stuck intermittently, eventually contributing to HGF. The fan comes on at either 85 or 95 degrees (I think) depending if its a 1.8i or VVC and that of course will be post the thermostat opening, so it seems odd that the fan should be on so early. Easiest way is a cooling system check at a garage to prove HGF or otherwise. I went on for months not knowing - eventually it was HGF but luckily there was no head damage.
Mike

My thoughts as to why the radiator was cold could have been for a couple of reasons. The system as its so long, must rely on some sort of pressure to help circulate the water together with the water pump, and if the cap was defective, this would also lower the boiling point of an otherwise pressurized system. After a drive the radiator would get warm and also hot... So that stat is definatly opening but could well be slightly open when cold, on my other cars the sign of this would be a cold heater but i beleive the MGF wouldnt show this up because of the way the coolant circuit it.

It seems odd that since refilling there hasnt been a problem, the only difference i made was REALLY tightening the old cap on the tank, usually you would see the coolant bubbling in the tank and really swirling around, but it sat stable.

I think as a precaution i will change the stat aswell. Has anyone removed the small relief valve from the manifold also?
Gareth

Gareth;
I have a MG TF 1.6 and I´m suffering the problems that you have but I add cooling liquid every day, so I´m interested to know if you have fixed the problem.
I´d like to discard a HGF.My engine has 53000 Km and less than 3 years. Any suggestion will be very apreciated.
Lopez

This thread was discussed between 30/11/2005 and 15/12/2005

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