Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Cold Engine


I have a problem on my 65 MGB, since I own the car it wouldn´t get the proper engine-temperature, exept in hot weather conditions. (Temp stayed at about 70 degrees Celsius instead of at least 80).
Now that the summer is over the temp wouldn´t even rise over 60 anymore, although I have already blocked 3 quarters of the radiator with cardboard.

First thing I did was change the thermostat (used about 4 within the last three years) to try and solve the problem, but it wouldn´t help.
So far I only know one other MGB that has a similar problem, while usually the cars tend to get too hot instead.

I also checked the gauge, but the temp it reads is accurate.

Any idea what else could be the problem?

Christian Mai

Have you checked the thermostats in a saucepan of water with a thermometer?
Stan Best

Hi Stan,

yes, I have checked them, worked properly.

The only thing I could do now (at least I was told so) is to remove the original fan and install an electrical one instead that is operated by temperature only..

Of course this would only mean to treat the symtoms, but not the actual problem.
Christian Mai

What temperature is the thermostat set to work at?
David DuBois

I imagine you checked the sender/gauge with a thermometer on the block, I think the electric fan is the only way to go.As for treating the symptoms, the MGB is overcooled in cold weather, we know this because without radiator blamking it will not come up to temp. My car will run fine in freezing temperatures with less than 1/4 of the radiator blanked off. The heater will keep the cabin warm as well. I have the original 3 blade fan and had the usual MGB problem of gauge going off the scale in slow traffic in the summer until I fitted the Moss shroud.
Stan Best

It won't come up to temperature in cold weather because of the surface cooling of the block and sump from very cold air (which I wouldn't have thought Germany had got yet anyway), not from the radiator. If it *is* that cold the thermostat shouldn't be open anyway. Blocking of the radiator restricting the flow of cold air over the engine, not through the radiator, is what gives the improvement.

Having said that I've never had any problem with getting either my roadster or V8 up to temperature with snow on the ground (and much colder with the V8), nor do they 'overheat' in summer, although the gauge will read slightly lower or slightly higher in extremes of both.

Likewise fitting an electric fan is unlikely to give much improvement, where these *do* have a benefit is keeping temperature *down* in extreme conditions like slogging up mountains in summer i.e. lots of load and relatively low forward speed.

As David asks just what temp stat are you fitting (should be 82C/180F)? What is the indication on the gauge during warm-up? And how and when are you measuring the temperature of the coolant? Both mine show a steady rise over 2 to 5 miles to N, then a sudden drop as the stat first opens, then cycling up and down (stat closing and opening again) progressively less as the whole system reaches equilibrium. After that it will go up a bit going up long hills, and down a bit going down long hills. This is also indicated by the temperature of the top hose and top of the radiator, getting slightly arm during the initial rise of the gauge, then suddenly getting very hot as the stat first opens.
Paul Hunt 2

Another issue - do you have the right temperature sender? There's 2 versions, early year and late year. They are interchangeable in the block, but as I understand, due to differences in resistance values and gauges, will give different results. I had the opposite problem with my 78 after replacing the temp sender; it always ran hot (about 3/4 of the way up the gauge) no matter what. I changed it out for a new late model sender and now it runs right in the middle. It may be that you have a late model sender that reads lower than the early model for your gauge. Just a thought.

J. Lawrence

A '65 should have a capillary gauge, rather than electric.
Dave O'Neill

"I also checked the gauge" How did you check it? A temp gun would be the trick here
If it really is low by the temp gun, block off the whole radiator. I use multiple pieces of lexan with duct tape hindges to adjust the size if it heats up on the highway or on hills RIC
Ric Lloyd


I have the same issue with my supercharged MGA. I have to cover 3/4 of the rad to get to operating temp if the ambient temp is below 15C.

It's something the cars originally suffered from when new, and the ones that overheat have coolant passages clogged wit calcium deposits and rust from years of use.

I am going to try an 80 degree thermostat when I can lay my hands on one.
dominic clancy

This thread was discussed between 15/11/2006 and 18/11/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.