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MG MGB Technical - My B doesn't like queues

Hi. My BGT overheats when stuck in jams. The rad, pipes etc have had little use; I've got water wetter in the system and I've run the heater even when the air temp is high so... I'd like to know
a)What electric fans owners recommend and
b)Has anyone got one for sale,please?
J. I. Jones

First there are some basic cheap checks.1 Timing 2 is the fan on the right way round, if it's pushing air not pulling through the rad. 3 Change the stat. 4 backflush the system, at the same time check the rad, the core could be clogged up or the cooling vanes disintergrating. 5 refill using the heater inlet to remove airlocks.
c cummins

I had this problem quite dramatically on my ´63 roadster, and checking out all the very relevant points in c cummins post above did not help at all.

Some weeks ago I finally got around to install a plastic fan shroud from Moss, and that seems to have cured the problem.

Part 60 here:
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=152&SortOrder=84

I have not been in any real traffic jams since, but have simulated it by letting the engine idle for a very long time after a good run, and the temperature now increases very slowly. I have not had the patience to find out how far up it will go, but when it reaches 195 degrees F and I rev the engine to a steady 2000 RPM, the needle goes back towards 190 again. Very comforting.

The shroud was a pain to install, I had to cut out pieces from it to make it fit properly on my car. But I am happy to have solved the problem in a simple, mechanical way that does not reduce the cooling when the car is at speed, like a pusher fan in front of the radiator does.

Tore
Tore

Firstly what do you mean by 'overheats'? It isn't overheating if the needle moves up from N, only if it starts steaming or losing coolant.

If it *is* steaming or losing coolant from the overflow then there is a fault. We haven't had it anywhere near hot enough to cause this on a correctly functioning system - or would be likely to, these cars run in desert states without overheating. Fitting an electric fan is only covering-up the real problem, and may not even do that. Have you replaced the radiator cap? A friends 15lb cap lifted at about 5psi, a new one solved his coolant loss.

If it is only getting higher on the gauge then you can expect that when stuck in traffic, even in a UK summer, it should be able to go up to the start of the white 'H' band before you get coolant loss, but I wouldn't expect it to go past about half-way there at worst. It is still worth measuring the temperature of the coolant as you could have an over-reading gauge. Not so likely with the mechanical gauge, but still possible. Sounds like you have the mechanical fan system i.e. with the radiator cap on the radiator, easy to put a thermometer in the coolant when the gauge is showing high and compare. Still be careful removing the cap of course, thick cloth over it, turn very sloooowly, when you hear hissing stop turning until the hissing ceases then turn slowly again. If coolant bubbles out then immediately retighten, in which case it *does* seem to be running too hot.

Two potential causes of this - either the engine is producing more waste heat than it should, or the radiator can't get rid of it.

In the former case the ignition could be retarded, or over advanced, or mixture problems. Could be combustion leak into the water jacket i.e. head gasket.

In the latter could be incorrect or badly corroded water pump i.e. insufficient coolant circulation. Could be blocked block and head water passages, or water passages ditto.

Maplin were selling laser-pointer infra-red thermometers quite cheaply a while ago which are useful for measuring the temperature gradiant across a radiator and showing cool (blocked) spots as well as coolant inlet temperatures.
Paul Hunt

I have the Moss shroud fitted and have been very pleased with it, I was watching the gauge today while queuing to get into the Uxbridge Show, the needle stsyed painted on the dial which made the waiting a lot more tolerable. The 4.2 E type coupe in front of us was clearly suffering with overheating or sooted plugs. I don't remember much about fitting the shroud so it can't have been that difficult.
Stan Best

I guess my problems fitting the shroud may have been caused by my car, built in february ´63, not necessarily the shroud. But the instructions that came with it says that the centre bottom part of the shroud may be removed without any significant reduction in cooling efficiency, so I guess trouble like I had is not completely unknown to the makers!

Tore
Tore

As others have said, an electric fan is just masking the problem. Paul has listed the potential causes.

Earlier this year I was queued for a considerable time in 40+ deg C temperatures and did not boil. (Did get hot of course, up to around 220F on the gauge.)

To clarify another point, fitting the fan the wrong way around does not push air through the radiator, unless the engine is running backwards. It merely reduces the efficiency of the fan somewhat.

Regards,
David


David Overington

"needle stsyed painted on the dial"

Now if all gauges were like that people wouldn't be so paranoid...

David is right about fan orientation, mine was the wrong way round for years until I noticed it and fitted the correct spacer for the short-nose pump (with a short-nose pump and no spacer the metal fan *has* to be fitted the wrong way round or it hits things) but didn't notice any difference. What *did* make a surpring amount of difference, but we are barely talking the width of the N, was fitting the foam between the top of the radiator and its mounting panel.

Someone mentioned changing the thermostat, you can check these easily by warming up from cold. Whilst the engine will warm up gradually the radiator shouldn't, but then when the needle gets about 2/3rds the way towards N it should suddenly get very hot. They normally fail stuck open, but if it *does* happening to be opening but only partially you will find the bottom hose is cool.
Paul Hunt

Years ago I stopped the engine getting warmer than normal by fitting a new radiatorcap (rated 13psi). The old one was loose fitting with no pressurisation as a consequence.
Willem van der Veer

This thread was discussed between 18/07/2009 and 20/07/2009

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