Radiator efficiency

[Tom Ward]

I've been having temperature issues on the B for a number of years. Running at motorway speed for any length of time has the temperature gauge rising until the point I'm no longer keen to let it go any further and I back off. The car hasn't been used much in the last three years as we carried out a load of bodywork but in that time I changed the head gasket and refreshed the coolant, flushed everything out, fitted a new thermostat and as the old temperature probe on the temp/oil gauge seized itself into the head I ended up putting a new gauge in.

The car went to Gaydon and back this weekend which resulted in me driving almost the entire length of the A14 at 50mph yesterday evening which was not fun but hello to everyone their B's who waved as they passed us at 70 . The new gauge is graduated in degrees rather than C,N,H. It's reaching 105c before I back it off from where it stops rising and maintains 95-100c at 50mph.

Having been through the entire cooling system I am becoming more convinced the radiator is simply not capable, on B roads, sitting in traffic and driving in town the car has no issues. Early in the morning where the air temp is cool it's also fine, it's just at any kind of sustained speed at warmer ambient temps it suffers. The rad was new 6 or 7 years ago and it really hasn't done many miles. It came from a reputable parts supplier (who also run an MG club for their owners).

I know the timing is a little advanced which will introduce some heat and I'll get that sorted and test it again before I do anything drastic but I would think it should still be able to cope.

Is there a way of testing it and proving the rad is low on efficiency before I try an alternative?

[Not_Anumber]

If you havent done so recently unscrew the coolant drain plug and check behind it for build up of crud. Mine was running a bit hot and I was convinced it must be the radiator at fault as I had flushed the system thoroughly or so i thought, via the top and bottom hoses.
I checked the drain plug as a last resort and was surprised to find some build up behind it. Once this was cleaned out and i re flushed with the plug removed this time I noticed a significant difference to the cooling efficiency. Not saying you have missed this but quite a few people do.

https://mgb.tips/2019/02/01/engine-bloc ... rain-plug/

[Ian F]

That's definitely worth doing - if you can get any coolant out of there!
When I rebuilt my original 18v engine I failed to dislodge the material blocking that drain hole. I even resorted to running the engine until hot with the plug removed and never got a drop out.
Fortunately the engine always runs at the correct temperature. I ascribe this partly to the oil cooler which was factory fitted when built.

IanF

[Ian F]

To try and sort out the heating problem you have there are a couple of things (at least) to ask/consider:
# do you have an oil cooler fitted?
# I take it that the original gauge indicated overheating, so the problem is not likely to be a faulty gauge?
# do you have the fan fitted the right way round?
# when running hot can you stop and feel the radiator temperature. Is it cooler at the bottom as it should be?
# water pump/fan belt operating as they should.
# check plugs - could be running weak at motorway speeds which could cause overheating. Are standard needles fitted?
# get the timing set correctly!!!

Ian F

[Bumpa]

It's a bit of a weird one. Most cars overheat when stationery, not at speed when there is a gale blasting through the radiator. The cooling system as standard should cope with UK temps easily. After all our American cousins use them in places like Arizona and Texas! My B only gets hot when stopped and the electric fan brings it down quickly. At 70 mph the gauge reads about 180F - it's an older gauge, the same as 82C.

[Ian F]

Agreed Mike. That's why I thought it could just be some engine parameters which were very outside spec. at motorway speeds. Perhaps very weak or the ignition timing way off. What do you think?
An engine running at high speed will generate more heat, but as you say, the airflow at speed should be able to remove that heat.

Ian F

[Dave Wheatley]

I've always thought that my car's cooling was marginal.
For example, in Dumfries town traffic which is not exceptionally busy, the gauge quickly zooms up to over half way, and the fan cuts in to bring it back down again fairly quickly.
By comparison, when I had a modern, a Vauxhall Astra diesel, the gauge never seemed to move in congested traffic, and the fan never cut in.

[Bumpa]

Dave, I don't think your B is behaving abnormally. I live in Troon, so about 80 miles north of you, and my B would do exactly the same. What you have to realise is that on a car of the MGB's age the temperature gauge shows you what is actually happening under the bonnet. You stop the flow of air by travelling slowly and the engine gets hotter. That will happen to any combustion engined vehicle. It would be most odd if the temperature stayed the same when the cooling system is basically stalled by lack of air flow.

On any car made after about the eighties the temperature gauge is electronically controlled not to rise above the mid point unless an extreme temperature rise is detected. In normal motoring, particularly in stop-start traffic the engine's temperature will fluctuate but the driver is prevented from seeing that in case it worries him/her.

On my '71 B the gauge is from an older car and is entirely undamped, so not only does the temp show the real situation, but the oil pressure gauge works in real time too. When the car is idling the oil needle flicks between about 40 and 60 psi as it shows the function of the pump in squirting pulses of oil. As soon as the revs rise the gauge steadies out because the pulses merge into one stream. It's fascinating to watch.

Now my V8 GT is a different kettle of fish. Those engines fill the engine bay and produce prodigious amounts of heat. The temp gauge on mine rises rapidly in slow traffic with the fans running continuously below 30 mph. Once, stuck in a queue on a very hot afternoon in France the needle of the temp gauge entered the oil gauge zone, but the car didn't overheat, didn't blow off any coolant and kept running as sweetly as ever.

[Allan T]

Have another read, Mike - it's as Tom's travelling at speed when, as you say, you'd expect a car to be well cooled - that he overheats and has to back-off, not when he's idling in traffic.

[Bumpa]

Yes I know Allan. I was replying to Dave's message - that's why I started with "Dave"!