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MG MGB Technical - Running Temperature.

Gents,
I have a 74 1/2 RB roadster, 18V engine, engine fan removed, kenlowe fan fitted to cut in half way between normal and hot. Last weekend with the sun out and the temperature about 20c i did a 60 mile trip. While driving the temp gauge reads approx 3mm past the normal. If i slow down to a crawl or stop the kenlowe fan cuts in after about 5-10 seconds. Is this normal or do i have a cooling problem, especially with the hotter weather we 'should' have this summer. Thanks for your interest. Chris.
Chris82

Chris. When you slow or stop the air movement through the radiator obviously does the same. With a mechanical fan this wouldn't matter, but with the electric fan the engine heats up which causes the electric fan to cut in.

In the Australian summer my system cuts in at about 95 degrees C and regularly runs when stopped. Mine is wired up straight of the battery and runs for about 3 minutes when the engine is turned off.

Sounds normal to me.

Tony
Tony Oliver

Chris mine is the same as Tonys and I have no trouble in an Ozy summer. Adjust the fan thermostat to only come on when close to hot (95c). Then on a trip it may never come on but will be there when needed.
Otherwise your better of with a mechanical fan.
Denis
DENIS4

I have a pair of fans on my '73 B/GT that come on: (1) when the A/C compressor comes on; (2) when the radiator sensor tells it to come on (temp?), or (3) when I use the switch I put on the console for that purpose. We drove the car across the SW US deserts in the hottest part of the summer last year and I never used the manual switch. Normally, this car has never overheated, but on that trip last summer, I saw the temp gauge needle disappear at times. The US MG guru is John Twist of University Motors here in Michigan, and he says to put a piece of tape over the temp gauge and rather watch the cracks between the bonnet and the wings. If there's no steam coming out, the engine is not overheating.

The weather we drove through was well in excess of 100 degrees F (37 degrees C?). Temp gauge be damned, we made it without any problems. John explained to me that (1), a 7# pressure cap on the radiator raises the boiling point by 21 degrees F, and (2) the use of antifreeze (half and half) raises the boiling point substantially further. Modern cars frequently run normal at 240 degrees F, whereas the "N" on our late-model MGBs refers to something in the ballpark of 180 degrees F. But our MG 1800s prefer to run at much higher temps. If they aren't blowing steam, they are not overheating.

FWIW,
Allen

PS: Did I mention that despite John's assertions, that gauge scared the h*ll out of me! But faced with no alternative, I followed John's advice and found it to be right on.
Allen Bachelder

This does sound a bit soon for the fans to cut in. I would back flush the rad and see what happens as a first step.
Stan Best

I'd have said 3mm past normal is a bit high, although RBs tend to be higher than chrome and all are different anyway. My RB V8 runs fractionally below the middle of the N and the roadster several mm below, in the temps of 23 and 24 we have been having lately.

In itself it's not a problem, the electric fan is supposed to cut in as the temp goes up, and if it brings it back down again that is all you need. Unlike modern cars for various reasons the temp gauges on MGBs aren't rock-solid and do go up and down according to ambient temperature and imeediate driving conditions i.e. slogging up a hill or cruising down. Half-way to N isn't a problem, but if it starts getting further towards the H then you would need to consider if it is the usage that is the problem (i.e. ambient and/or load) or a fault. And as Allen says if they aren't steaming or losing coolant then they aren't overheating, which many forget.
Paul Hunt2

Hi all,
The radiator was new last year as were the hoses, thermostat and radiator cap, and i am using 'all seasons' fluid. I have a 13lb cap fitted and although this may make no difference, is it the correct one for the year of my car(centre fill rad). Thanks again, Chris.


Chris82

Chris. There is a tech article on cooling systems on my website, www.custompistols.com/cars/ which may be of use to you. Anti-freeze has a cooling efficiency of .6 as compared to pure water which is rated at 1.0. Thus, in our hot conditions (110 deg. F and more), I run a lower concentration of anti-freeze than I would in a colder climate.

This being said, I have checked out several cars which showed indications such as yours and caused the owners to worry. Using an IR thermometer, the cylinder head was measuring less than 190 deg. F when the temperature gauge was about the 3/4 point. Old gauges, old sending units, old wiring. Not a particularly accurate combination.

Like the rest, I would not worry about it unless you can actually document that your engine is running near the boiling point of plain water. Running at about 200 deg. F has, in tests I have read, significantly lowered the wear that takes place in the engine as it is running. Not a bad thing at all.

Les
Les Bengtson

This thread was discussed between 09/05/2008 and 15/05/2008

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