Cooling System

Al Richey/Andy Waller

Many of you will have seen discussions on the forum about the cooling system.  Many of us found that the the cooling system is very efficient and was running at 73C probably because of the large radiator.  Now, 73C is really too low and it is generally recommended that you maintain higher than  80C so that volatiles in the oil are burnt off. The Rover temperature spec for the engine is 88C. You can do this with a combination of the thermostat, the fan switch and the grill.  I fitted an 82C thermostat, an 95C thermostatic switch and I put a fairly coarse stone guard grid on the grill to reduce air flow.  Mine now runs at a steady 92C which is good.  For comparison Andy also runs an 88C thermostat, but has a variable thermostatic fan switch currently set to about 94C with sensor in the top hose, and he has partially blocked off the front grill with removable plastic card.  His system now maintains a steady 88-90C.

Incidentally, air locks can be a problem that prevents good cooling. The top hose is higher than the radiator and this is often where air gets trapped.  If you can squeeze the hoses at this point to remove air, or fill the system through one of these joints, then it will help to bleed the system and ensure it is full of coolant.  I had an experience whereby an air lock was created and it completely covered the water pump preventing any circulation.

However, we all find that the warm up time was excessively long, of the order of 12-15 minutes. So on short trips we are damaging the engine.  The culprit is the tube across the top of the engine.  The problem with that is it means that from the start you are bypassing the thermostat with quite a substantial flow of water being cooled by the radiator.  

However, Andy has done a 'proof of concept' change by blanking off the top middle radiator outlet and moving the spare 'heater return' hose down into the bottom cooling hose by inserting a 'T' section next to the water pump.  His system now warms up in about 5-6 minutes, less than half the time.    So this is a good modification to carry out.   Here are the before and after diagrams to illustrate the modification.

BTW, the radiator is from a Rover SD1.  It is still available from Rimmer Bros at the very good price of £85.  The is a great deal compared with other radiators and you might think it worthwhile to buy a spare one before they run out of stock.