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MG MGF Technical - High temp warning system

Having had my F now for just under six months and having loved every minute so far I'm still living in constant fear of HGF. It's 1997 R plate which I believe are the most succeptible.

Having been on here daily since I got the car and doing plenty of homework I'm well aware of the risks and I do as much as I can to avoid them (Never over 3000rpm till warmed up etc).

What I was thinking about last night though was some kind of buzzer/ alarm that would sound if the engine temp went over a certain level. This would be more noticeable than checking the temp guage every 30 seconds or warning light on the dash.

Has anyone ever tried this or considered it. If the gasket did go and your were warned early enough then you could stop and minimise the risk of the head warping etc and reduce repair costs.

I wouldnt know where to start though in doing it. Obviously the buzzer/ alarm would be easy enough to obtain (maplins) but where to fit it is my sticking point.

Should it be connected to the temp guage itself or is this too unreliable. I'm not sure my temp guage is 100% accurate as even when I'm thrashing it it never goes over 100 degrees.

Any advice appreciated.
Bob Millar

I have a simple comparator circuit. This basically compared the voltage from the temp guage when it was slightly above the normal position with a reference voltage. It also has a stabalized 12 v source to eliminate any slight changes in the battery voltage.

Pretty simple to make though beleive me it wont help that much if you have a major hgf. Reason being ther is so little water in the block that the temp rises very fast indeed.

Worth installing for a bit of peace of mind but after what I just suffered it wasn't going to make one bit of difference. Oh it did go alarm by the way.
S Laithwaite

>>Any advice appreciated. <<
Don't worry about it - just check your coolant /oil levels on a regular basis. My '97(P) blew its headgasket around '99, and has been fine since; I don't pay particular attention to warming the car up or treat it with any more care than other road vehicles.
A low coolant-level warning may be more useful than a high temperature alert if you're looking for a project.

My car may be a 97 but it's only done 26k so it's just a young pup really!
Bob Millar


I spoke to Andy (SF) about this last week. My idea was to fit a TC inside one of the coolant tubes and display the temp on a small LCD display. There would also be a 'trip' point which would activate a relay for whatever use. buzzer, lamp, etc.
The only down fall of this would be if all the coolant empties, there would be no coolant to measure!

your thoughts?


It should be possible to connect some kind ot temp sensor direct to the engine (thought I'm not sure where) but my initial thoughts were to use the existing temperature gubbins to minimise the work involved.
Bob Millar

I had been told that the guage is slow to react. This would likely mean that the sensor is slow to react. Not knowing where it is I can't comment. If thats not the case then your idea and S Laithwaite comparator would work a treat (maybe). There is a buzzer that is about the size of the fog light switch, which would fit in the blank, if youve not already used it.


the Temp sendors are attached to an elbow of ally bolted onto the 'back' of the engine on the exaust manifold side, without water, because the ally does not conduct temp very well, the temp gauge will not give a fast and realistic idea of the head temp. a better idea might be to put a sensor in a pool of oil actually under the cam cover.
Will Munns

Check out Tony Thompson's site for a warning alarm circuit

Bruce Caldwell

Temperature is only one symptom of a HGF - and is not terribly specific. :o(

Rather than detect the problem after it has occured, you might be better off trying to avoid the problem in the first place. For this, you'll want either a remote thermostat or a new TF pressure sensing thermostat, a water/oil cooler (to match the head and block temperatures more closely), and a system to keep the coolant circulating after engine switch off...

Working on the above list. The next service could prove very expensive in terms of new parts!!!
Rob Bell

Does the old drilling holes in the thermostat trick offer any benefits?
Bob Millar

I've heard that it does (one of the MG race guys suggested this option to me) - but others seem less convinced (Simon Scutham for one - find him on the Lotus Elise BBS).

The advantage of the drilled thermostat ring is that there is always a flow of coolant what ever the state of the thermostat bulb. Result is that the temperature oscillations that one tends to get with the standard cooling system is somewhat subdued - but they still occur. Bad news is that the time to warm up is prolonged (engine wear, fuel economy and emissions all increase) - and if you over do the drilling then you may as well junk the thermostat all together!

It is generally accepted that the remote thermostat option is the best bet - and Carl has a very neat solution for the MGF - see Dieter's web-site:
Rob Bell

Rob, RE your temp sensor problem

What have you decided? I have been thinking about the problem and the useful locations, I think that they're all inside the head!
Will Munns

Will - yes, you are right - the best place for monitoring head temperatures is to have thermocouples in the head waterways. That simply is not going to happen.

Compromise then: monitor the water temperature coming out of the cylinder head. It's a long way from being ideal - but probably the only way forward for our planned 'field tests'

Only other thought that comes to mind is an IR temperature probe to map the external temperature of the cylinder head...?
Rob Bell

My thoughts ;-) There are 18 places where it would be good to have a sensor, 10 of them are oilways, 8 of them are waterways. The oilways are 5 on each side of the block, they alow the oil to drain down from the head and would give you an idea of the temp diffrence across the head, end to end and front to back. you could dangle sensors in the olways from above, this would require removing the cam cover, getting the wires out would take some stealth, but could be easily acheived by using very thin wires and feeding them thru the 'oil seperator' (wire gauze) and out thru the front breather which leads to the air filter.

If you were interested in the waterways then you could play the same trick, but you would have to pull the head off, thread the wires in thru the water outlet and one into each waterway (8), four on each side, then use a drill bit thru some ally pipe to get an almost perfect fit and then silicon sealent to make it water tight.
Will Munns

Given that a common HGF on the F is loss of coolant to the outside world, then where are you expecting to see a change in temperature ?
I still believe that the earliest indication of a problem is to monitor coolant level - and this is not too difficult.
The head gasket may not even fail during normal operation - it could fail during cool down, esp. if engine is already hot (coolant may not be over-temp before switch off), or it may fail during warm up when temperatures are not stable, and you will need signifiant operating data to program temperature sensors to pick this up.
If you look at the signals from HT leads, injectors and lamda sensor, then it's not too difficult to spot a dead / malfunctioning cylinder (esp a pair of cylinders, such as 2 and 3).
I do like the idea of the electric pump running after engine off - you may even be able to rid of the thermostat by using electric pumps.


Steve said:

> >I do like the idea of the electric pump running after engine off

The project is to do exactly this Steve. The challenge we face is to try to measure the effectiveness of such a pump once the engine's been switched off. We want to be able to do back to back tests with the pump operating and without to see what difference there is.

So, any ideas? This is what Rob's quest is about.

I presume the easy option is to run the pump for X minutes after stop. No point making it complicated and only running when hoy. "kiss" as they say.
That'll surely stop the suspect hot spots causing problems.

As for measuring...
A random (and possibly bad thought)... what about using a standard "low light" camcorder with a heavy IR filter. CCDs pick up heat. With a heavy IR filter you'd block visible and the CCD would record the IR?
Ok... so it's a random wine induced thought... :o)
Worth a try?

Or... measure by inference:
Ass: Lotus use elec "post-off" pumps on the vhpd engines (I think)
=> they know their stuff
=> they can make funky measurements like that
=> they don't spend money for no reason
=> they must have solve a problem
=> it's bound to be a good thing to do
RAA: fit the pump and feel that it's doing good.
;) ;) ;)

Paul Nothard

This thread was discussed between 10/09/2003 and 15/09/2003

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