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MG MGB GT V8 Factory Originals Technical - Water Temp

Hi everyone, having sold my MGA Roadster have now just got a factory GTV8. On the way home from getting it a couple of times the water temp gauge went into the red then went back to the Normal straight the way,this happened 3 times in a trip of approx 90miles on the MI happened again 2 times following day on a trip of 60miles coolant level ok and has Bluecol in, no cracked or damaged hoses,steam pipe ok, am thinking of changing the thermostat and fitting a fan override switch anyone got a suggestions.cheers guys oh and a happy new year.Derek
derek cotton

Your stat is probably going south. I'd replace it soon. You can probably test it in a pan of hot water if you want to watch it bind as it tries to open. Its a comon problem, and a cheap fix.

You may want to flush the system while you're at it. There may be something in the system causing the stat to bind such as casting fragments, a bit of sealer, or some old stop-leak.
Jeff Schlemmer

Could it be an airlock behind the temp sensor ? used to get it sometimes in my V8 Conversion. Used to remove radiator plug, speed up the tickover and add water. Would produce some bubbles and ok again.
Ian Sanders

derek cotton

Classic symptom of a blocked steam pipe, BT, DT, a couple of times. You say it is OK, was that a visual inspection or did you disconnect one end and physically check that both ends were clear? Whilst adding a manual fan override switch can give peace of mind it only protects against fan switch failure, if the coolant is hot enough to need the fan it will be running. It is a quirk of this steam pipe blockage that it sends the temp gauge into orbit but does not trigger the fan switch, this is because the coolant *isn't* anywhere near as hot as the temp gauge says it is, and running the electric fan constantly won't stop the temp gauge cycling. The thermostat would have been well open by then, IMHO, if it were stuck closed you would have boiled, lost the coolant, and the gauge would have stayed high at that point. This will happen after only a few miles of running, the temp gauge rises towards N as normal, then continues going past it and into the red.
Paul Hunt

Pt.2. How did you check the coolant level? If ever some characteristic of the engine changes and you start investigating things you must always remove the radiator filler plug and check the coolant level in the actual radiator. Checking the level in the expansion tank is OK for routine checks but there can be coolant in that tank but the level in the actual rad, and hence the engine, can be low under some fault conditions. Again BT, DT. However if low coolant in the engine is the problem the temp gauge will continue to fluctuate and get worse, so given your couple of occasions each trip I doubt that is the problem. Because of the problems I had I installed a low-coolant sensor in the radiator filler plug, and I would recommend that over the fan manual over-ride switch. *Don't* bother fitting one in the expansion tank, as I say you can have coolant there but not in the engine, which is far more important to know about! I have the override switch as well, an illuminated one so I can also check the the fan switch (at least) has operated when the gauge starts rising in traffic. But since solving a couple of cooling problems have never bothered using it even in the hottest conditions.
Paul Hunt

This thread was discussed between 01/01/2005 and 03/01/2005

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