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MG MGA - Under cooling!!

Last night I saw that my water temperature which had been solidly in the 180 degree area all winter was now reading 140-160 degrees with an outside temperature in the 70s (Farenheit).
No water loss and the pump still seems to work.
Looking through the archive I can see that there are 2 possible solutions, either the thermostat has fialed and the radiator is now permenantly open or the gauge is faulty.
Anyone with any experience on this.
Will swap out the thermostat tonight as I have a spare and see what happens.

Neil
Neil Purves

I suspected my gauge was under reading, so I put into a pan of boiling water, and bingo, it read exactly 212. I mention this as I believe the gauge/bulb is so simple it does not fail often (unless the capilliary tube is broken).
Now the thermostat - if it fails doesn't it remain closed? Therefore it would cause overheating, not under cooling.
Peter.
P. Tilbury

Hmm. After an hour of swearing at the thermostat housing I eventually have swapped the thermostat and... no difference.
The temperature has now settled at 120 degrees F which leads me to think that the gauge is faulty.
The weekend will therefore see some testing with boiling water.
I guess that after 48 years of use it can fail!!

Neil
Neil Purves

Join the overcooling club. I run 50C on a cold day unless I cover 2/3 of the rad area with a sheet of cardboard. It was completely normal before I fitted the Supercharger.

I swapped to an 80C thermostat, no difference. I covered the oil coller, no difference. I thought it may be the (cr*p quality) Moss radiator, which I returned for a refund after the third one sprang a leak inside a year. The original spec rebuilt original rad (which doesn't leak) made no difference either.

I can only assume that better breathing is causing the car to run cooler - even on a warm day there is sometimes ice on the outside of the carb, which is in the same position as the rear carb on a standard car.

Maybe I need to remove the heat shield

Thermostats now fail open, so it should be that. If not, yours is a mystery - must be something in the water!


dominic clancy

Neil, -- it sounds like you are in for a gauge rebuild. The temperature gauge is internally actually a pressure gauge. It works on vapor pressure of a volatile working fluid. If the sensor bulb or connecting capillary tube spring a leak the fluid is lost and the gauge stops working. It is VERY common to break the capillary tube.
Barney Gaylord

Thanks Barney, I am now checking out who can repair this. Any suggestions welcome.
I would also appreciate if anyone knows what thread is on the water sensor as I want to block the hole when I remove the sensor bulb. I normally use the car daily and with the weather being nice I don't want to have it off the road for weeks.

Neil
Neil Purves

We have a few well known vendors here in the States, but I dunno about your side of the pond. Try Googling instrument repair.

For the sensor nut my thread gauge says 18 threads per inch. A 5/8-18-UNF nut screws onto the sensor nut just a little loose, as the OD of the sensor nut thread measures 0.610-in (not quite 5/8-in). I don't have a 5/8-18-UNF bolt hand to try in the head, so I can't guarantee it.
Barney Gaylord

speedycables.com in the UK
dominic clancy

This thread was discussed between 08/05/2008 and 12/05/2008

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