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Overheating problems with an MGBGTV8
Andrew Egerton-Smith (Tahiti Blue 2610) from Norfolk sought help with continuing problem of overheating in traffic. This note is based on the responses provided by Victor Smith (Harvest Gold 1089) from London SW. (Mar 03)

Andrew Egerton-Smith contacted the Editor saying "I am about to put my V8 on the road for the new season but prior to doing so I write for your guidance on the continuing problem of overheating in traffic. A new water pump is about to be fitted but recently I saw an article in a classic car magazine which road tested a secondhand MGBGTV8 and mentioned the car was fitted with an uprated radiator to overcome the traffic overheating problems. I know these cars were always prone to this difficulty but I am put off from using the car if there is any risk of heavy traffic, even in rural Norfolk. So this does reduce the times when it can be used. I have fitted a manual override switch to the cooling fans so I can switch the fans on in anticipation of slow traffic, but after a few minutes of heavy traffic jams, the temperature gauge starts to rise! The other answer may be to check the gauge but this has always acted in the same manner so I do not think this is wrong. I have stripped out the underbonnet insulation in an attempt to allow the heat to dissipate. Can you please help me solve this difficulty?"

There are replacement radiators available with four rather than the standard three cores which have proved very effective at reducing the heat build up on an MGBGTV8. The topic of curing overheating difficulties with the MGBGTV8 has been extensively examined over the years, and most recently the available options were reviewed by Gordon Hesketh-Jones in his comprehensive V8 Workshop Note 248.

The key question is how does the overheating problem arise and what degree of overheating is normal? When the design team was creating the V8 at Abingdon back in the early 1970s, they realised quite early on that the space available for the radiator was insufficient for the size of radiator needed for cooling the V8 when the natural airflow was low - when the car was stationary or in slow moving traffic. So rather than go for a bonnet blister or bump as had been the solution for the earlier MGC, they chose to fit two electric cooling fans. Most members find the cooling water temperature rises rapidly once a V8 is in slow moving or stationary traffic and then they hear the reassuring roar of the fans as they cut in! In normal circumstances the needle on the temperature gauge then moves back to the vertical whereupon the fans shut down. If Andrew's V8 is getting hot in traffic and, even with the cooling fans on, they are not bringing the temperature down to a moderate level whereupon the fans go off, then there is clearly a problem with the cooling system that requires careful investigation.

The diagnostic approach I would take is as follows:

Expansion tank. It is essential you do not overfill the expansion tank. It should be between a quarter and a third full when cold. If it is too full then you can get syphonage


from the radiator and then consequent overheating.

Position of the electric fans. It is essential the fans are located as close to the front face of the radiator matrix as possible as the cooling effect is very much a factor of that proximity. Clearly the fans will need to be set back by a sufficient margin to avoid any risk of physical contact between the blades and the matrix.

Sludge in the radiator. Over time there will be an accumulation of sludge in the radiator which can reduce the efficiency of the radiator. The sludge can be removed by flushing the radiator with a flow of clean water preferably with the unit removed from the car. Don Hayter reminded me on a journey to Longbridge during the V8 25th Anniversary week in 2003 that you should also flush the engine block too!

Temperature sensor. If the fans are coming on later than you feel might be correct - they should cut in with the gauge between 5 and 4 o'clock - then it might be wise to check the temperature sensor. On the V8 this is an Otter switch which is a very basic bimetal unit with a "bowler hat" cover. It is not an expensive item to change.

Thermostat. To replace this unit you will need to consult V8 Workshop Notes 2, 15 and 248.

Water pump. As the cooling effect depends on the cooling water being pumped round the engine block to absorb heat and then onto the radiator to dissipate that heat, clearly the water pump is an essential unit which has to perform well. There are several V8 Workshop Notes on replacing or repairing this unit - see Notes 1 and 246 for example.

Andrew has a rubber nosed V8 so the oil cooler will be underslung and located in the airstream through the cut outs in the valance. With chrome bumpered V8s, the oil cooler is mounted in front of the radiator and some members have repositioned their oil coolers underneath behind the valence unit. I have never found that necessary.

Jeff Ward (Flamenco Red 2375) comments that a significant improvement in cooling results from fitting a Special Tuning air dam (original ST part number STR0189, available from Moss as a "pattern part") and repositioning the front number plate up from its original position under the rubber bumper and on to the rubber bumper. He feels this is essential to ensure there is an unobstructed flow of air through the duct in the air dam and onto the oil cooler. Jeff's V8 has been fitted with an ST air dam for 25 years and he reports that "in addition to reducing temperatures, the "recovery time" down to normal running temperature after running in slow traffic is very short indeed".

He adds "for my money, the air dam is an inexpensive modification which does not spoil the looks of the V8 - it was an ST option after all - and it works! It needs respraying to match the body colour of course". Jeff also adds that if you have a manual override switch for the fans, then it enables you to always switch on early.

See also V8 Workshop Note 293