Considering these cars have a reputation for overheating and running hot, certainly in the hotter Australian and tropical environs, (and as I believe even in their home country, the UK) they have the potential to make motoring in them an undesirable and unpleasant experience.

Many theories have been expressed about the causes of overheating, from bad tuning to loose leaking exhaust manifolds/systems and dirty blocked radiators. Certainly these motors need to be tuned properly and have clean radiators, but once tuned they are very efficient (for their era). Apart from the tuning and dirty blocked radiator aspect I dismissed all other theories about overheating.

Before progressing further it is ESSENTIAL that the motor be tuned properly, and the radiator MUST be cleaned properly, NOT JUST 'BACK FLUSHED'. This can only be achieved by taking the radiator out, having it dismantled and physically cleaned by a professional radiator repairer. BELIEVE ME, IT IS WELL WORTH THE EXPENSE.

I must point out that from the outset my motor was scrupulously cleaned and totally reconditioned as was the radiator. That way I started my experiments knowing that there were no inhibitions from 'external environmental factors', ie dirty and contaminated/blocked water galleries.

With all that in mind I devoted a considerable amount of time and effort into developing a system that would make the cars cooling system more efficient. My aim was to do this with a minimum of external modification.

At last I think I have "cracked" a major part of the problem, maybe even with that hopelessly inadequate cast aluminium fan! That fan will be the subject of further experimentation.

Eventually the most serious problem that became obvious was the thermostat bypass hose that goes from the engine side of the thermostat housing, to the BOTTOM RADIATOR TANK. All this 'thing' does is effectively inject VERY HOT coolant into the cooled bottom tank coolant, and because of the size of this 'pipe', it effectively heated it again, possibly even to 50% of what it was when it came out of the motor into the top tank. This is then sucked out of the radiator bottom tank, and pumped back into the motor by the pump. With it being
SO HOT it is an inevitable consequence that the harder the motor is worked, the hotter and hotter it is going to get !!!

I achieved this by blocking off the bypass pipe, and by drilling a 3/16" hole in the body flange of the modern thermostat I am using.

BINGO, I am now running at a constant 165 deg F, which may rise to about 175 deg F (or maybe 180 deg F towing my caravan) on a very hard long uphill pull.

This result indicates to me that there is still some restriction in the flow of air through the radiator, and/or maybe the coolant from the motor to the radiator core. However at this stage the temperature range is within acceptable limits as set out in the workshop manual, so I will leave well enough alone.

I am using a modern "high flow" 160 deg thermostat, of 2 1/8" diameter (a "Tridon" brand, No TT2000-160, which operates at 160 deg F or 71 deg C). I made a brass sleeve that fits into the thermostat housing, in the machined surface and stop in the housing where the original thermostat fitted. This sleeve has a step in it to take the thermostat, and then another stepped sleeve that fits in after all of that to lock the thermostat in place, via the small bolt that was used in the original type thermostats. I have simply eliminated the hole over the bypass outlet, which effectively blocks the bypass. The hoses and pipes are in place externally, so it still looks authentic.

I am probably getting a better result too, because early in my experiments I fitted a 16" steel bladed fan, with 3" parallel blades, that has a slightly greater pitch than the aluminium fan, and also made a shroud to fit the radiator to enclose all the area round the fan. With this modification there is now a really good flow of air through the radiator.

Together with this modification and the blocking of the by pass pipe the results are as set out above. Unfortunately the down side is that the fan and shroud are the external modifications that are obvious to experienced Sheerline/Princess owners.

I feel that the blocking of the bypass pipe may even be successful (certainly must be some improvement) on a car with the cast aluminium fan, PROVIDING that the radiator is really clean and the motor has been de-scaled and cleaned.

In addition to all of the above I found that on really long hard pulls, ( and pulling my caravan) the temperature got up to about 180 deg F or slightly higher. At this temp it seems that the motor (or oil therein) is so hot that vaporisation of the fuel starts to happen. Once this starts the motor is starved of fuel, which causes lean running, which causes overheating, which causes more vaporisation and so the cycle continues at an accelerated rate.

I stopped this vicious circle by completely bypassing the mechanical fuel pump by installing an electric fuel pump. Since doing that I have not had the vaporising problems, and even on long hard pulls the car still seems to run about 3 to 5 deg F cooler, and there are NO vaporising problems.

Whilst I am not completely happy (at this time) with the results I have achieved, of a long hard up hill pull, or some of the extra load caused by towing my caravan, I can live with it with the modifications I have made. It seems to me that the temperature the car runs at is still influenced to a great extent by the ambient air temperature.

I intend to do some further experiments through the winter months, and there are a couple of other ideas I have in mind to reduce the operating temperature even more in the summer months.

When I have completed my experiments I will let you know the results.

Ken Gardiner.