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MG MGB Technical - Running Cool

Just fitted a rebored, reground engine with an unleaded head into my B.

All ancillaries swapped from old car, carbs, temp gauge etc.

Running beautifully, but temp gauge which used to be around the 70 deg mark sits at 40 deg. Should I worry??

It is a capillary pipe gauge.

Cheers.


Andrew Walton

Did you install a new thermostat? If so, you may want to be certain that it's closing. I installed a new one in my small block Chevy and had the same problem. It turned out to be defective right out of the box. If anything, a freshly rebuilt engine should run a bit hot until it gets thoroughly broken in. RAY
rjm RAY

Looks good,
Did you put a good thermostat in? Bit obvious I know but it has been done before.
But don't always assume gauges are accurate, but unlikely to be that far out if it was working before the re-build.
Allan Reeling

Feel the top hose while it is warming up from cold. While the gauge is rising it should barely get warm, then when approaching 80 degrees or so should suddenly get hot. That shows that the thermostat is closed during warm up, then suddenly opens, as it should.

If the top hose warms gradually right from the start then the stat is stuck open or partly so. Some stats have a jiggle valve to allow bleeding, which close when the system is full. But others have bleed holes which allow a small amount of coolant to circulate all the time, but they shouldn't be overcooling. Some thermostats again have no bleed facility, and they make the system a bugger to fill.

There again the gauge could be reading low if it is on the way out, that is what they do. The next thing after feeling the top hose, if the stat appears to be OK, is to get another thermometer and check the reading against your gauge.
Paul Hunt

This thread was discussed between 29/04/2015 and 30/04/2015

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