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MG MGF Technical - Thermostat drilling

A few month ago I bought a used MGF. MPI 1.8 with 50k on the clock and very nicely kept. Then I got in contact with the very few MG owners around here and was horrified with the frequent gasket failures stories. I have been told that drilling the thermostat may contribute to avoid that problem.
A few questions: 1. Is that a fact?, 2. Were is the thermostat located?, 3. Can I possible do it myself? (no MG dealer in Santiago at present).
I thank you in advance.
Chris Benson

Drilling the thermostat ring will certainly help Chris - but is not quite the cure. The best option available to to install a remote thermostat - and better still, obtain the late pressure relief thermostat from the mgtf (also fitted to Landrover Freelanders).

Returning to your original questions,
(2) the thermostat is located under the inlet manifold, to the right as you look in through the boot. Access is limited, but possible without having to remove the inlet manifold.
(3) Yes, it is possible to do yourself :o)

I'd recommend a remote thermostat though - more detail on Dieter's webpage ( and here:
Rob Bell

The thermostat page on Dieter's site is:
Myself I have som experience with drilled thermostats. Right now I use one with a 2.5mm hole in it which I think is slightly too large. I would recommend you to replace your current 'stat with an 82deg item with a 2mm hole.
But even better is of course to convert the system to take a remote thermostat, preferably the MG Rover PRT.
As soon as I can figure out the best way to plumb it into the system I will fit a Land Rover Freelander kit because OE MGFT parts are not easily available.
Jon F

Fully agree.

Notice if you drill.
- Go for hole below 2.5mm (Experiance Jon and Carl)
- Install the drilled with the hole as far on top as possible.
Why ?
On one hand this hole provides the wanted slight waterflow and on the other hand the hole allows whyever occuring air bubbles to drain in direction expansion tank.

Notice for better? options.
The remote thermostat as mentioned by Rob is latest state of design with the K-Engine.
Carl from Sweden is on the road with a similar installation since 4 years now.

Similar means, he got the short circuit for the water way near the radiator but uses a drilled 82 Thermostat in the old place.

The official from MGR for MGF and Landrover for Freelander ( )is the remote thermostat _near_ the engine and a simple big open washer at the old thermostat location.

Check above links and see at Carlos (Lotus Elise) aswell

PS. missing you on the MGF Owner world map @


Thank you folks. This forum is a most for us newies.
I realise that there is plenty information and have a lot to learn if I want to keep the car. I am now trying to become familiar with all the MGFs sites. A task indeed.
Interesting that Rover did not provide a solution for an apparently well known and frequent problem.
A relevant question to understand the prospect: Is any F out there, lets say with 100k, which have not had the gasket gone?
Grateful indeed. Chris
Chris Benson

>100k, which have not had the gasket gone?

of course :)
Mine hasn't got one. 100k km *only* though.

>> Interesting that Rover did not provide a solution for an apparently well known and frequent problem. <<

They did - but it took a very long time to reach it: the PRT thermostat :o)

Happy reading - there is a staggering amount of MGF stuff on the internet :o)
Rob Bell

Welcome to the world of MG'S and happy cruising

Page MGB K-series


How near completion is the project Ingemar? Certainly looking extremely good :o)
Rob Bell

Thank you. There is still a lot to do with the project, but hopefully I will
be ready around summertime.

>Which parts do I need for the start lock to work? Do you have any pictures of the parts?

Dooh, what a great project :)))

You've got the latest Engine Control Unit (affiliated useful car VIN may be printed on a sticker on the opposite site of the part) and the new design ignition lock with transponder included.
You miss
a alarm control unit (located behind the MGF/TF heater control knobs) coded to the above engine ECU
The MK1 looked like this
I think the one you need (MKII) looks similar with another sticker and connector arrangement ? (no pic)
a new design alarm blipper coded to the that alarm ECU.
the connector for Testbook programming
Black one top left.

Plus wiring harness, which unfortunately is included within the complete harness of an MGTF (or Zx).
And finally someone with an MG Rover Testbook to code the alarm ECU to the Engine ECU and code the key fob to the alarm ECU.

Good luck.

Please people let me know what do you think of this possible prevention of HGF that a technician from a former Rover garage has offered. He said that placing a second 80 thermostat into its own housing, in line to the original one, and without removing that, provides a known and permanent solution of the problem.
Thank you for your time. Chris
C. Benson

Chris - perhaps the technician can draw out what he's proposing? But it certainly isn't something that I've heard suggested before. If it is placed where I think he's suggesting, it won't work.

The second thermostat is a good idea - this is what Carl's arrangement is - a remote thermostat up close to the radiator. The original thermostat is retained in place, but with a drilled thermostat ring. This, Carl has shown to work - as shown by data recording. If you want to go down the remote thermostat route (and don't want to use the PRT thermostat assembly), then this is the way forward.

More details on Dieter's website :o)
Rob Bell

Rob, the man is propossing to cut the hose and interpose a second 80 thermostat in its own housing a few inches away of the original one. Not a remote one close to the radiator. Did not say anything about movilizing and drilling. I believe the original would remain untouched. Thanks. Chris
C Benson

Wow, Ingemar. You project gets all my respect.
I guess welding skills are required for such an endeavour! I know what my next evening classes will be!
by the way, where did you get the oil take of plate which bolts to the engine and has the two take off ports? Im interested,

David Peters

I have made all the details myself.


Off topic. Sorry:-(

It doesnt seem to have the openings at the same location as the original thats shown aside.
What thread size of fittings do you have at the block exit plate?

Would you be able to make another?

Did you make the alluminum stat housing with the flange yourself too? normally the K has a stat housing in plastis right. Does this alli one fit in the same place?

I already bookmarked your page *LOL*

David Peters

Chris, the pipe to the thermostat housing is metal not hose - so I am not sure how the technician chap is going to be able to do this. Also, is he planning to put the thermostat in-line with the current thermostat? That is what I don't understand...

I suspect that installing an additional thermostat like Carl's installation near the radiator is going to be easier (far better access!) and, I think, more likely to be effective.
Rob Bell

Thank you Rob. I really dont understand a thing about the problem. I gather that the proposition was to place a second thermostat in line to the original leaving that untouched. close to the engine I believed.

However, would it be effective to place a second remote thermostat, close to the radiator, without removing or drilling the original?

Most grateful, Chris.
Chris Benson

My alteration to the cooling system includes drilling of the original thermostat (or even better changed for an 82 deg.C drilled one!) IMO the drilled thermostat re-assembles the "old times" thermostats with a small "jiggle" valve that let any trapped air pass thru as well as a small but steady flow even at fully closed .
The state where the original thermostat is fully closed has been worrying me ,hence the drilling.
There are a few older cars with a suitable external thermostat that can be used as the one at the front radiator. Mercedes, Russian Lada (!) and old Rover to mention a few. Being older cars they also benefit from lower thermostat opening temperatures. Usually around 82-86 deg.C. Apart from the external thermostat a T-junction and a small piece of additional hose is needed for my set-up.Has been well proven both in ordinary cruising as well as on track-days.See Dieters site for more info and pictures.
/ Carl.

I have followed the thread with interest as two years back I had my Fs thermostat drilled in order to prevent HGF. Sorry to say that the drilling did not avoid HGF that happened 6 month later. And let me say that I usually follow every known recommendation like checking the cooling tank level, waiting for oil temp to reach 90 and many other. Remote thermostat may be the way to follow but rather expensive indeed.
WH Snyder

<<When mine was done MGR doggedly stuck to their guns saying "the gasket itself is a semi-sacrificial component which can be regarded as needing replacement during the life of the car">>

Is that a fact?. Now I am really worried.

Chris Benson. Santiago. Chile.

<"the gasket itself is a semi-sacrificial component which can be regarded as needing replacement during the life of the car">

I am sorry Chris but sadly the statement above is true. Maybe you could find out whether your car suffer HGF already and was fixed. My personal experience is that the first HGF is almost unavoidable but after have it fixed the probabilities of another one tend to decrease.
Andrew B

A second thermostat makes no sense. You will only achieve a restricted flow. The objective of the thermostat is not to include the Rad in the flow circuit until the engine is up to temp - putting two in is unnecessary at best, and dangerous at worst.

I have just completed the following modification this weekend, with a datalogger pulling temperature and speed data from the car:

1. Replace original thermostat with 'blank' - the blank is made by cutting the wax-capsule away from an old thermostat - leaving just a 'washer' with a large hole in the middle.

2. Fit a remote thermostat near the radiator - one that opens at a lower temp to take into account the temperature loss down the metal underfloor pipe. Obviously the thermostat is accompanied with a bypass tube.

The data is very interesting - im certain the modification reduces the chance of head gasket failure. The warm up cycle is not noticeably different. Major temperature differentials, and erratic temperature cycling is no more - The radiater performance is also improved - probably due to improved efficiency of the water pump; As standard the pump is 'sucking' coolant - there is a major restriction (bypass pipe, or thermostat), with no restriction before the pump it is allowed to work at full efficiency.

Interestingly, don't trust your temperature gauge - it is MASSIVELY damped - there are HUGE spikes in the temperature of various parts of the system which do not register on the temp gauge output from MEMs. The reality is quite startling.

Detailed logs and reports will follow soon - once I've got some webspace! (I have a bit of maths/manipulation to do first, there is 90mb of data on my logging equipment! - from two 1hr benchmark tests!)

And I guess, time will tell!



I read a comment above about remote thermostat being expensive.... bear in mind, not as expensive as a hgf though!!!
My whole setup has cost me about 40 - details to follow as I said above.

David Monks

Looking forward to reading more about your remote thermostat conversion, Dave.
Myself I am going to do the job this winter and I am trying to figure out the best way to do it. Did you fit a LR Freelander PRT?
Jon F

I wanted to specifically use a 'normal' thermostat - it needs to open at a lower temperature if used near the rad (to account for temp drop down the long pipes to the front.) I think the PRT is unnecessary - no other vehicle/engine requires such an unusual (and expensive) thermostat, so why should MGF and LR? Because it avoids having to solve the real problem! The cooling system is very badly designed.

I have used a combination of different manufacturers parts. I have made the thermostat housing using two 'normal' (bolt to block) housings - a pair bolted together to make an inline housing (skimmed first, and 0-ring sealed). Im using a 78oC thermostat from a 620Ti. Like I said, total cost has been about 40 - and (in my humble opinion) is better than kits supplied by QED etc.

Anyone got any ideas where I can get some web space for free to post my pics?

David Monks


Thank you for your idea just when I thought that my "drilling thread" was forgotten. With all the controversial propossals I got, have not decided what to do yet. Yours seems quite a good and simple solution may it really work.

Very few MGF possibilities here in Santiago. A bunch of MGFs only and everybody, including former MG Rover garages, think that the Fs are hopeless and not worth the effort. Now I can see why I got her really cheap.

Anyway, if I could prevent HGF I would go for it as really have begun to like the car.
Chris Benson

Drilling the thermostat will definately help with the thermal shock - but to get the stat out is 3/4 of the work towards going the whole way to remote thermostat anyway!

This thread was discussed between 08/01/2006 and 31/01/2006

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