Heater mystery - Solved

Here's something a bit different for you, especially those who like MG related puzzles. I've been having an annoying/worrying problem ever since the MOT.

So lets imagine I'm a new member who doesn't know a lot about MGF/TFs. What advice can you offer me?

HI,
I have been struggling with a problem with the heater in my MGF.
Sometimes it's OK, but 5 mins later it goes cold. Car warms up quickly and delivers warm air within 5 minutes from cold. Can be OK for a while, then the heater will go cold again.

Car appears to be running fine, it did lose some coolant somewhere (didn't find a leak) after the MOT; it did need an Italian tune up to pass emissions, so I thought maybe that was the cause. Anyway, I topped it up afterwards and it seemed to be OK.

Can you help?

David Aiketgate wrote: Here's something a bit different for you, especially those who like MG related puzzles. I've been having an annoying/worrying problem ever since the MOT.

So lets imagine I'm a new member who doesn't know a lot about MGF/TFs. What advice can you offer me?

HI,
I have been struggling with a problem with the heater in my MGF.
Sometimes it's OK, but 5 mins later it goes cold. Car warms up quickly and delivers warm air within 5 minutes from cold. Can be OK for a while, then the heater will go cold again.

Car appears to be running fine, it did lose some coolant somewhere (didn't find a leak) after the MOT; it did need an Italian tune up to pass emissions, so I thought maybe that was the cause. Anyway, I topped it up afterwards and it seemed to be OK.

Can you help?

Hi imaginary new member :silly: Welcome to the T Bar forum, we have a great team of guys & girls here than can answer everything (well almost!!!) could it be an airlock ? have you tried bleeding the heater bleed point and checking the front one too. is the heater valve manual or electric ? if manual is it opening properely/?? and not self closing, the same if it is electric. Another fault i have heard of before is a flap of rubber inside the flow pipe acting like a flap valve and closing off the flow. when was the A/F changed last?? Hope this helps :shrug:

Hi Bryan,
I've read all about air locks and I've bled both those points, there was a little bit of air in the heater and a bit more in the radiator.

Afterwards the heater was working great... for a while... now it keeps going cold again. I tried bleeding again but no air was found.

The heater valve seems to be working because when its actually blowing hot turning the valve to cold makes it blow cold and back to hot when I turn it to hot. Until it just starts blowing cold again. I had to top up the level in the expansion tank again, though.

Does the car show any signs of over heating?, Could be the water pump isn't running efficiently and unable to pump the water up into the heater matrix.

However if the car is running fine as you say, the problem must be with the heater/matrix itself, As Bryan mentioned there's few options in that area which could cause it.

We'd love to see a picture of you car and
:welcome2:

Psymon wrote: Does the car show any signs of over heating?, Could be the water pump isn't running efficiently and unable to pump the water up into the heater matrix.

However if the car is running fine as you say, the problem must be with the heater/matrix itself, As Bryan mentioned there's few options in that area which could cause it.

We'd love to see a picture of you car and
:welcome2:

Very good point, the MGOC had an MGF in with HGF and found that the impellor had fallen off the water pump (it dropped on the floor when they took it off!!!!) and the coolant had not been circulating much at all and resulted in a "Cooked Engine" :bust:

Thanks Psymon,

No overheating, and when the engine's running there is a good flow of coolant from the bleed screw, and still no air in there. Also a good flow back into the expansion tank.

Seem to have lost a bit more coolant somewhere, topped it up.

This is my car, by the way.

Any more ideas?

Nothing new from me to add i'm afraid, You'll need to wait for some of the other members to pass through.

Having said that the coolant must be going somewhere, I'd plump for either there is still more air in there somewhere or its escaping via the expansion tank cap.

Should the cap hiss?

Not all the time, I'd double check it has been refitted corectly after topping up the coolant, If its fitted fine replace the cap.

Right, thought I was getting somewhere. I replaced the expansion cap with a new one from Mike Satur. The hissing has stopped now and the system seems to be holding pressure fine. No more coolant loss, no air in the system, checked at all points.

Ran the car up the road and kept a check on the heater pipes by removing the cubby box. The heater pipes got hot very quickly and lots of heat from the heater. :thumbsup:

However on the way home the heater went cold again. Checked the heater pipes the top one was hot but the one underneath was only lukewarm.

No air, no leaks, no hissing from the cap.