Very hot engine!

[Munch_84]

Hi All,

I'm completely new to MGF's and i've just bought one and totally in love with it. I know they are prone to Head Gasget and cooler problems. My engine seems to be much hotter than any car i've had before and it makes me nervous as my temperature guage has stopped working. Also the coolant tank apparently needs to topped up regularly.Th HG was replaces 2 years ago so hoping it's not on it's way out again, anyone got any ideas?
Also incidentally the heater doesn't seem to work?

Thank you!!

[adrianclifford]

Sounds like it could be an air lock as that would answer several questions, F's and TF's are fiddly to bleed if you don't know the cooling system layout.
You may have a coolant leak explaining the reason for topping up, the heater not working and the apparent hot engine, what temperature guage is not working, oil or coolant ?

If you continue with this you may force the gasket to fail again, that's what it's there for.

[Chris Tideswell]

As Adrian points out it sounds like air is getting into the coolant system, re-bleed the system and replace the coolant cap as this is the number one fail point.

[adrianclifford]

True, the cap should be changed annually (I keep forgettting about that as mine is). I always carry a spare too should I be able to help out anybody.

[Munch_84]

Thanks all! Doesn't sound too scary! It;s the coolant temp guage that's not working.
Legends, ta!

[adrianclifford]

Pretty important though Munch, the F/TF doesn't hold a lot of water, so a small loss could be substantial.

[Bandit]

Unbolt the engine cover and just off the end of the cylinder head is an alloy casting with rubber pipes running from it, and two sensors attached. the brown sensor sends a temperature signal to the ECU for fuelling etc and the other, either blue or black, is the feed for the temperature gauge. The voltages & currents are very low so a slightly feeble connection can result in no gauge response, a generous squirt of electrical contact spray into each side of the connector could possibly fix it but the sensors do fail occasionally so that's the next most likely cause. Not expensive, IIRC £12 odd, an MGR dealer can usually get one for next day. If you have a multitester it may be worth checking the reading you get across the terminals when the engine is hot against the same reading when cold - if they're different then the sensor is working and the fault lies elsewhere.

When you say "heater not working" do you mean you can't get hot air out of the vents (i.e. only cold), or the blower doesn't work? The control knobs are a push fit onto the shaft of the underlying switch, but can fail and lose their grip so turning the knob doesn't actually change anything - particularly common on the temperature control.

[Munch_84]

Yep, no hot air out of the vents. Ok i'll have a rummage tonight and see how it goes, thank you all.

[Rob Bell]

Assuming that the heater valve has not siezed or that the control knob is rotating on its spline, then this suggests that there is a considerable amount of air in the heater circuit, preventing water flow.

If the temperature gauge is reading cold, it might be possible that the reason for this is that it is not actually 'seeing' the coolant, but is simply sitting in a pocket of air.

I wouldn't drive the car again until you've had a chance to fully bleed the coolant circuit - http://mgf.ultimatemg.com/group2/coolan ... cedure.htm

I'd also be tempted to use an MoT gas analyser to check for hydrocarbons in the resevoir tank - if there is, and I suspect that there might be here - then you've got a problem with the sealing of the fire rings on the head gasket - which is either a gasket or a cylinder head problem.

Cylinder heads can be porous, due to casting voids. It is possible to reclaim a cylinder head - either through peening and then skimming the cylinder head (more here on Tim's excellent how-to YouTube video), or skimming and using a head-save shim. Or you may be unlucky and require a new cylinder head...

Any way, probably getting ahead of ourselves here - but certainly some important investigations to be undertaken!

Good luck, and let us know how you get on!

[Munch_84]

Right progress. I realised my carpets we wet so think it may be a leak in my heater hose that's causing the level to drop so dramatically. This still doesn't answer the hot engine question but getting there. Also realised my brake lights are staying on so going to have a rummage with the switch to sort that out tonight. Does anyone know how easy it is to acess the heater hose?
Cheers all

[Rob Bell]

A heater hose leak is a possibility, but unlikely. It's steel inside the car, and the ones I've removed from 13-14year old MGFs, these pipes have been in pristine condition. They run within the 'transmission' tunnel. The easiest way to get to them is to remove one or preferably both the seats (not absolutely required, but will make working on the interior that much easier) and then take out the T-bar and the transmission tunnel trim.This exposes the gearbox selector cables and the hoses/pipes to the heater.

Although the pipes may be perfectly serviceable, it is possible that the heater matrix itself may have failed? Not heard of this, but entirely possible...

Wet carpets usually mean a failed weather seal - either soft top or heater box air intake. I suspect that the carpets being damp is a bystander to the main event - but certainly worth a look!

[Bandit]

I'd definitely agree that water in the footwells is very unlikely to be escaped coolant, it is almost always rainwater. The heater matrix & connecting pipes would in all honesty be the last things I'd check when looking for a coolant leak - lack of coolant getting to the heater matrix won't be because it's leaking out before it gets there, if it was you'd be driving a paddling pool...