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MG MGF Technical - Thermostat to be drilled?

Because of a cooling fluid loss I took my regular MGF 1998 to a garage as people in this forum advised to do ASAP. The original black manifold gasket has not been changed yet and they will replace it for a newer green one. Radiator, coolant pipes and hoses are apparently fine.
Now the garage people have suggested that while there might be convenient to have the thermostat drilled as an easy and very cheap way of preventing a head gasket failure. I am very interest on your opinion about.
Edward Lyon

Pretty good news then Edward. I contemplated the same course of action a month or two back and was advised against on here for reasons I can follow.
A better solution is the fitting of the PRT(which I haven't got around to yet). It costs slightly more but is more of a 'proper' solution rather than a nothing bodge. Hopefully our Chinese chum, amongst other experts, will persuade you with some of the better reasons for the PRT route.(Thanks Will!).

A drilled thermostat is a modification that the racing guys have been doing for years - and works - to an extent. Just be wary of how many holes you drill, and how large - else the engine will never reach operating temperature!

See Dieter's website ( for more detail on this.

But really, I agree with Charles. A remote thermostat, and particularly the MG Rover PRT, is the best approach to preventing future HGF. Kits are available from LandRover that can be adapted for the MGF, or you can use the mgtf PRT found fitted on cars from late 2003 onward.

Cars with this new type of thermostat are very unlikely to suffer HGF from what we've heard from various servicing experts.
Rob Bell

I would go for the drilling. The PRT may be more effective but is very expensive and not easy to get hold of one. After the second HGF on my F I was advised to get the thermostat drilled -one hole 0.3 mm-. That was four years ago and since then everything goes fine.

300micrometre hole? Are you sure Nick? That's very small.
Rob Bell

I would have thought 3-5mm was more likely.
Steve Ratledge

There has been at least one poster who suffered a further hgf despite having his thermostat drilled during his original hgf repair.

Have a look here for the details of the prt and drilling.

The PRT comes in 3 parts

PCH002960 Top Hose assembly
PCH002970 Bottom Hose assembly
PCH002790 Heater Bypass assembly

about 60 but labour for fitting it will be more.

Jon Baker

I think Neil meaned 3 mm. ;)

IMO the drilled thermostat is/was one of the _early_ options to smoothen the engine temperature grade when heating up from cold.
Also it was good to release air bubbles (as long as the drill was located on top of the thermostat.)

The PRT or other remote thermostat solutions looks like the more reliable solution and not so expensive.


I think a drilled thermostat is an improvement to the cooling system as it reduces the temperature transients in the cylinder head. I used to have one with a 2.5mm hole in it, the only disadvantage was the very long time it took to obtain working temperature at low ambient temperatures.

Now I have fitted a Land Rover Freelander PRT kit that I have adapted to fit my MGF. I chose to fit it horizontally and it was was a fairly easy job. Works great!
Jon F
Cost me very very little, works well, and data to support claims.
If you don't want to mess around with the hoses in the engine bay (difficult and expensive) do it this way. If you don't want to make the remote thermostat housing, buy one (100ish) or get one from a mid 80's BMW (20ish).

David Monks

David - this reminds me - do you reckon we can meet up for some telemetry measurements on Dave's car equipped with the MG PRT and electric water pump?
Rob Bell

Rob, 2/3 weeks of running now after my up-front PRT. Looking good in this hot weather already.
How difficult is telemetry, I need to know what is going on down below!!
Jerry Herbert

I hear that the MGOC and Rog are working on a PRT kit for easy DIY fitment. sounds like something I will have to do once they come available
Neil list a DIY PRT kit for 152.75
C Tideswell

How does that price compare with the LR kit I wonder?

Jerry, telemetry ought to be pretty easy - Tim and I were working on a DIY laptop interface... but the devil is in the detail... I am hoping to see whether we can borrow some professional equipment. Not sure about timings just yet though.
Rob Bell

The Elisparts remote thermostat kit can also be modified to fit.

A simpler remote thermostat may be that offered by QED, becuase it is a "generic" K series remote stat, whereas the Eliseparts one needs some work to be made to fit the F/TF.
James Reinhardt

How straight forward would fitted this PRT thermostat be to a ZR160 do you think?
Lord Sward

Probably easier to fit a Freelander kit as that too is front engined :o)
Rob Bell

easy fit ?
LOL... ;)
The DIY problem isn't fitment but removing the old thermostat and swapping in the washer instead.

The PRT is easy fit with short circuit at the front if someone worries with works at the rear.

See at Carl's from several years ago.

This thread was discussed between 26/06/2006 and 11/07/2006

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.