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MG Midget and Sprite Technical - Thermostat - holes or no holes?

I am about to replace the thermostat on my mildly tuned 1275. As the climate has changed (seasonal) my car is running too cold with the temp guage barely rising off the start peg. It currently has an 82C degree thermostat so I am replacing it with an 89C one for the winter.

Only question is - is there a common consensus on whether to drill any holes in the new thermostat when using with an MG Metro head (no head by pass connection). I had a single 5/32" hole drilled in the old thermostat but it never really picked up to a proper working temperature - it usually runs at around the lower calibration mark on the gauge in the summer. Unless of course my gauge is reading low, but I don't think so as the electric fan very rarely comes on either.

Guy
Guy Weller

I use the pass through pipe on the manifold and don't think it matters if you drill or not

At one time I didn't - no overheating temp stayed OK

then I did drill, no difference - temp stayed OK

but now you'll get hours of apocryphal tales to pass the entertaining evenings

Is all OK with you and yours in the Big Wet?
bill sdgpm

Yes Bill, we are OK where I live, but for many it has been a devastating week with a long "recovery" time to get through yet.

Being impatient for a reply, I just went ahead and put the thermostat in without drilling it, on the logic that it is easier to add a hole later if needed, than to remove a hole if not required! If nothing more, I am anticipating toasty-toes and an improved "demister" function!

Guy
Guy Weller

I drilled a small hole or two, I seem you recall you might have told me to do it, Uncle Guy!
Keeps a small amount of coolant flowing.
Tarquin

Very likely Tarquers. Just because I tell you to do something doesn't mean that I know what I am talking about! Maybe at the time I thought it was a good idea for summer conditions!
Guy Weller

Hi Guy,
What is the pipework layout for the later heads without a by-pass line?
Peter
PJ HOBSON

Peter,
The by pass I was referring to that is missing from the later (MG Metro) heads is the very short hose between head and the water pump.
Guy
Guy Weller

Im a fan of the 1/8th inch little hole myself. esp. during summer. Ive done it my my truck and it runs alot better plus there is never or vary little pressure on the radiator so Id imagine the head gasket likes it also

But I think on the midget, your making a good move to wait till next summer to add the hole...and it only takes 10 minutes if you need to.


prop
Prop

I fitted a new thermostat wich had no hole. What happened was that temp went up and then suddenly dropped back to cold, I think that was the moment when the thermostat opened. So I drilled a hole later and now temp rises gradually, although not to high.
I have the by-pass blocked.
Alex G Matla

I drilled a couple of holes in mine - temp gauge runs just slightly over normal in the summer, but I replaced the fan with a lekky one with manual switch, so that may explain it.
Geoff Mears (1970 Midget)

Hi Guy,
Back to the plot.If holes are made in the thermostat, by the OEM, they are there to vent air out of the system.
If the OEM did not supply one with a hole in it then do not drill it.

Gardner engines years ago used a similar type wax thermostat incorporating a 'Jiggle Pin'. A very small hole had a 'loose' T shaped pin through it with a small ball end on the underside. When filling the system air vents past the pin, but immediately the water fills the housing it lifts the ball up and seals the hole off.

Any hole you make extends warm up time, not a good idea. Leave the heater tap fully open on start up, this should help to vent any air trapped in the engine, and, all the air BMC designed to be trapped in the heater matrix prior to start up. When filling from 'dry' never drive the car to get the stat to open, you do not necessarily know just how much air is still in the system that yet needs to be purged. If you get excessive air entrainment around the impeller the pump rotates but the water does not. This is probably why we occassionally get weird symptoms that mysteriously right themselves.

When buying stats, for those with a by-pass, you need the correct stat. When the stat opens it's supposed to close off the by-pass inlet port so all the coolant goes to the Radiator. If your stat does not have the by-pass "shield" that moves up to close the port when the main valve lifts then change it. (Water takes the shortest route to maximum water pump suction
ie down the by-pass line, even though the stat is fully open and most water is going via this route as well).In this situation the cooling system control becomes a lottery, but quite entertaining!

Peter

P.S. I bet a lot of you have wet feet this weekend!

PJ HOBSON

Just got back from a 90 mile test run. I put the stat in without drilling a hole this time. Bled the air out as I filled it (antifreeze, this time around) using the bleed nipple that I have added to the top heater hose for the purpose. A few squeezes of the large rad hose also purges air out of the system pretty quickly! Incidentally, this is another advantage of using Daniel's silicon houses - they are soft and pliable enough to enable this, unlike the standard rubber hoses.

Thermostat now seems to work fine. Running a little warmer than before which is a good thing - needle now steady at the mid-point on the scale. Fan cut in once when in standing traffic but otherwise remained inactive with the temperature self regulating. Heater nice and warm, ready for the weekend drop in temperature!

Guy
Guy Weller

Guy
Which bleed nipple did u use ??

This is a mod I have thought about doing many times, there are some neat ones on Peugot/Citroen models, maybe there is a hose that has one that is a suitable substitute for the top heater hose.

Anybody know one that fits ??

Ian
Ian Webb '73 GAN5

Ian, A scrap-yard one. Not sure now but I think it was off a Citroen
Guy Weller

Guy,
Was the 90 miles to get across the river?
How is the situation, are REME and Wimpeys on the job yet?
Peter
PJ HOBSON

No Peter, I am in South Cumbria and although there were severe floods none of our road bridges have been washed out. The 90 mile round trip was, for a time, what residents of one side of the river in Workington were faced with if they wanted to get to the other side of the missing bridges!
Nobody rebuilding bridges yet. There has been talk of getting REME to put up a bailey bridge but no activity on this as yet.
Guy Weller

This thread was discussed between 25/11/2009 and 26/11/2009

MG Midget and Sprite Technical index

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