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MG MGF Technical - Heater control valve sucks!

As has oft been stated the F/TF heater control valve design is hopeless.

It attempts to control the flow of hot water into the heater matrix but fails miserably, it's either full flow (hot) or nothing (cold)

I live in hope that one day somebody will bring out an improved version - but I'm still waiting.

They couldn't possibly try and sell the new NAC TF LE500 with the same arrangement - could they?

If NAC have come up with a better heater lets hope it may be retro fittable eh!

John Thomas

No heater where the temperature is controlled by a water valve is going to be very controllable. Many modern cars have an air-blending heater where the heater matrix is permanently hot and the temperature is controlled by mixing hot and cold air. This is much more controllable. Quite honestly I was amazed to find when I bought my MGF that it still had a water valve heater. I suspect it was the cheaper option. If ever a car was developed on a minimum budget, it was the MGF.
Mike Howlett


I have a sofisticated climate control system with ECU, and a plethora of sensors, aspirator and blender motors in my Range Rover. IT IS USELESS!

Heater on my MGF is much better! IMHO


Sam Murray

actually it does make quite a bit of difference, I can tell a difference of about "one hour" from hot and fully hot. Perhaps you're using it to heat the car with the roof up and don't need anywhere near as much heat (it doesn't rain that often here in cambs)

Anyways, you'd stop complaining if you had to use the heater in the midget - one fan speed, only heats one leg and to control the power you have to open the bonnet to get at the tap!
Will Munns

I agree, Mike, that the air blend solution is best as it offers instant change in air temperature particularly from hot to cold - but a variable temp matrix system should also also work albeit with a very slow hot to cold response time (as all the heat must be dissipated from the matrix).

Almost all heaters were water valve controlled once but had fairly decent range of temperature adjustment.

The problem with the current system could either be down to the design of the cable activation mechanism or the water valve itself.

Maybe someone (Dieter) could dismantle the current Rover valve to see how it works?

Bob Muenchausen has fully researched the MGB equivalent - see his excellent article at

Perhaps we should see if we could fit an MGB valve !

John Thomas

If the valve on the F is anything like the one on the 400 (and there is no reason it wouldn't be exactly the same part) it is far more simple than the B one, consisting of a shaft with a hole sideways thru it which rotates at 90-deg to a pipe, the cable is clipped to the metal bracket on the valve so the angle of attack gives as liner a motion as is possible from forwards/backwards movement
Will Munns

Thank Will

If it is the same as the 400 one, and I assume the 400 heater control is better, then the lack of space to fit a decent cable control mechanism in the F will have presented a challenge.

The resulting odd shaped cam adjuster
won't make for smooth adjustment.

And to respond to your earlier comment - yes the heat adjustment is only an issue with the roof up.

With top down I either want it fully on or fully off !

John Thomas

I assumed that the odd shape cam was an attempt to make the control feel more "liner" as 2x water flow will not cause 2x heat
Will Munns

Is this a new John Thomas or the old one relocated??

As far as the heater is concerned - I agree it is rather unsophisticated BUT used in conjunction with the speed control on the blower it is adequate.
Ted Newman

Hi Ted - it's the old one, retired to the sticks last year.

I see we first contributed to this BBS 10 yearss ago and indeed you opined on this very topic in November 1997.

Plus ce change .. eh!
John Thomas

Hi John - like you I too have retired to the country (relatively speaking from Islington to Woolwich Ar*enal).

Actually I think we contributed before 1997 it is just that the BBS Archives only go back to then - my first venture was asking about going to Silverstone in 1996 or the fact that I had to let The Green Squirrel go back to Longbridge in April 1996 for 'adjustments' to the floor pan.
Ted Newman

I think it was Bruce who developed a climate control system for his airconditioned F - and that was still using the existing heater valve IIRC. He sent me the directions which I could probably dig up for anyone who is interested?

Personally, like John, I probably only use two or three heater settings (off, full-on, or approx 1/3 on with the roof up on a cold day), and only three speed settings, off, 2 or 4 (more often either off or 4, which possibly explains why I am still on the original resistor coil pack 13 years after the car was built! LOL)
Rob Bell

The problem with the unbelieveably nasty ventilation in the F is that you can't get any fresh air into the cabin with the hood up, which is why I freeze when J opens the window.

The problem with the unbelieveably nasty heating in the F is that heating varies with speed. Drive faster, get hotter. Drive slower, get cooler. There is no such thing as the correct setting on an F's 'heat' control, you just have to fiddle forever.

It would have cost about 25p to get fresh air to the central vents (just as the B did several generations ago), and about 1.50 to use a decent set of heater controls pinched from the parts bin.

Perhaps you should be looking to a nice Volvo Kes.
C.R.B. Simeon

There's no such thing. The heating/ventilation in the F is dire, no matter how much we care for our cars.


I thought you were a hardier soul than to let a little heating problem worry you :-)

Ted Newman

Ted, the old bones are not quite as hard as they used to be. All I want is cosy tootsies and a little fresh air to the chops. I even get that on the R80G/S.



Don't get too soft!! My two wheels are pedal powered only these days - but I do take a peek in the Triumph shop from time to time:-)
Ted Newman


You said you thought the cam design was to make for a more linear heat control - what it seems to do is make fine adjustment difficult when the peg sits in the cam depressions.

This seems to lead to all on or all off options, with finer adjustment you might be able to find a happy medium - needed when the hood is up

If the water valve rotates thru 180 degreees from full on to full off(?) could one design a different attachment mechanism.

Is it the same design on the 200/400?


John Thomas

This thread was discussed between 08/01/2008 and 01/02/2008

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