MGA-Register

Overheating

Overheating is a problem that a great deal of MGA owners suffer from at one time or another. I’m talking about the cars by the way. I had the misfortune of suffering this very problem some years ago on the Regency Run which is an annual MG event starting in London and finishing on the sea front in Brighton. I’ll cover my solution later. In this tech page we can hopefully highlight some of the more common problems that can cause this phenomenon. I couldn’t help noticing the increased number of phone calls and e-mails regarding this subject that we received during a recent hot spell, a nice change for the British climate. The following points have been extracted from the Register’s Technical Manual. For details of this and other regalia go to our Regalia page on this site.

Before getting too worried about an overheating problem check that your timing is correct and that you have no blockages in the cooling system. If these are all okay then you might have a greater problem.
One problem that has been known to cause overheating is the radiator core. We had reports of one such instance. An owner in Australia had a radiator in his car that had a slow leak. Eventually, he decided to have it re-cored. His local radiator expert fitted a core that he thought would do the job but hey presto, instant overheating. He took the car back to the radiator shop and after various tests they found another core nearer to the original specification. This was fitted and his overheating problem disappeared. The theory was that the fins on the first radiator were too close together and were impeding the airflow. The second core allowed better airflow and hence cured the problem.
I mentioned my problem on the Regency Run. The run took place on a very hot Sunday and as Brighton is a popular seaside resort, not only were there 250 MG’s on the road but Joe Public, the kids, his granny and the family dog. This inevitably led to a jam and after several stops the old temperature gauge started to climb until eventually the poor old MGA would pull away without spluttering. I believe this is due to fuel evaporation. The only thing I could do was pull over and let him cool down. My solution was to fit a Kenlowe fan, which I wired into the Fog Light switch keeping the dash looking original. Now when I get stuck in traffic I simply pull the F switch to start the fan which holds the temperature at about 190°C until I am able to move off.
Geoff Barron had a similar problem, his car had been running fine when one day it started to overheat. Geoff hadn’t touched a thing on the car to cause this. He made all of the usual checks but found nothing until he ran the engine with the pressure cap off. There were bubbles gurgling away at the radiator filler mouth, this could only mean one thing, the head gasket. The head was removed but nothing found so he took it to a local machine shop who found a hairline crack. He fitted a new head and the problem was solved.
Another cause of overheating can be the fitting of the wrong radiator pressure cap. The MGA has a fairly long reach cap. It is quite a common error to be sold the wrong cap with a shorter reach. When you fit the cap it does not seal correctly. As the cooling system relies on the pressurised system allowing the water to pass its normal boiling point, the water boils at its normal temperature and floods out of the overflow.
Another problem that has been known to cause problems is the use of a reproduction Grille. Some of these tend to have the slats bent at less of an angle than the original, which restricts the flow of air into the engine bay. I often wonder about the fitting of club badges directly onto the Grille as this must also reduce the benefit of the Grills slats. A lot of MGA owners do not bother fitting the large ducting pipes just behind the Grille which take air up to the Carburettors and Heater. There is a theory that this allows a lot of the cooling air to escape around the radiator. There has been a suggestion that it may be an idea to fit a rubber strip between the top of the radiator and the Bonnet (Hood) similar to the Twin Cam. Some of these causes only become apparent on a hot day.
If your thermostat fails in the closed position, it will allow the engine temperature to rise very quickly and boil over. However this is a quick cause and remedy.
If someone tells you to remove your thermostat, remember that you may need to fit a restrictor otherwise the water flow to the radiator could be decreased and allow the temperature to gradually rise.
Another way of cooling your engine is to fit an oil cooler. This will not solve your overheating problem but it will help the engine to run a little cooler.
Since I posted this feature I have had one owner who mentioned that he removed about eight years of dead insects from his Radiator core. His car now runs a lot cooler.

I hope these few points may have given you a possible solution to your overheating problems.See the next item for another members view on this problem.