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MG MGB Technical - sips antifreeze and runs hot

Hey good folks, the 73 MGB runs very hot and seems to sip some coolant. Is it worth a try to re-re-torque the head? Gasket, cracked head or block? Whats the conventional wisdom? Thanks, Tom
Thomas McNamara

Have a carbon monoxide test to check for head gasket leak. This will tell you right away if it is an internal problem.
Sandy
SANDY SANDERS

Also compression test.

But 'hot' is totally subjective. Where on the gauge, and have you measured the actual coolant temperature in the rad when the gauge reads N? Electric gauges can easily read high for a number of reasons not associated with hot coolant.

My V8 tended to run hot, and burp coolant out of the overflow on switch-off unless I kept replacing the cap. Eventually I was getting air (not combustion gases) in the system which was pushing coolant out all the time it was running. However that was an external expansion tank system, shouldn't happen with the pressure cap on the rad. After a lot of time and some work I came to the conclusion that the water pump was sucking in air. It's much cooler now with no coolant loss. Check the hose (particularly bottom) clamps are tight, by slackening then retightening them, not just by trying to tighten them as they could be seized but slack.
Paul Hunt 2010

If your head gasket was leaking your radiator would be pressurised to the point that it blew water out of the overflow pipe. How much water does your car use ?? It may be worth changing the thermostat to see if this lowers the temperature at all. How old is the radiator, is it clear and have you back flushed it recently. It may be worth giving it a good clean out to see if this improves things.
Iain MacKintosh

Hey Good folks, thanks for the input. It seems to "peg" the gage. Does sending unit resistance information exist? The radiator is about 6 months old. The engine has about 15oo miles since the rebuild. How hot should the rediator be? What is a cabon monoxide test? Thanks, Tom
Thomas McNamara

Resistance depends on what gauge and sender is fitted, there were at least two types of each and if you get the wrong combination it will read wrong. Hence the first step in investigating running hot on the gauge should always be to measure the actual coolant by another method. Ralph from Germany posted the figures for his pre-77 MGB some time ago, and these include 20C/68F/885 ohms (cold), 85C/185F/82 ohms for 'N', and 110C/230F/41 ohms for 'hot'. Like many changes things are confused, but the only time both sender and gauge changed together was for the 77 model year. The sender insulator changed from black to red, but some sources give the date of this change as 71/72 and others 77. The gauges changed from needle down to needle up in 77.
Paul Hunt 2010

This thread was discussed between 26/05/2010 and 27/05/2010

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