I have solved the problem! Originally the fans wouldn't come one even under an overheat condition, but after checking the operation of the computer by replacing the temperature sensor with a resistor, the fans seemed to be working. They came on at a simulated temperature of about 240 F. The gauge read high at 255 F, and was in the red by 266 F - it was difficult to adjust the simulated temperature precisely. The problem that remained was that with the thermostat in place the engine quickly overheated. (In the meantime I had a leak from the thermostat housing, which was due to a damaged seal. I think I must have damaged it trying to withdraw the housing without disconnecting the hoses. I was able to replace it with two standard o-rings, one on top of the other, and a bit of silicone to hold the outer one in place. I also discovered that you don't have to remove the serpentine belt before removing the alternator, saving a lot of time - one has to remove the alternator to get at the thermostat housing.) I think I mentioned that I had disconnected the heater, since the hose had burst. (That probably precipitated the original overheat.)
Someone said that the heater provides quite a bit of cooling. I must admit I didn't really believe that, but since all else had failed, I decided to try reconnecting the heater. I had to use generic hoses, which was a slight problem because on one hose the two ends are different sizes. Anyhow, it cured the problem! Now the engine maintains a temperature close to 220 F (105 C), just as one post mentioned, but I can't see why. It is very surprising to me that the thermostat is adjacent to the inlet from the radiator, at the bottom of the engine. That had me thinking that the flow was out of the bottom of the engine to the top of the radiator, but the temperatures of the pipes show otherwise. It rather appeared that the thermostat was not opening with the heater disconnected for some reason. Perhaps someone can explain.
There seems still to be a slight leak of coolant. I am hoping that it is not the cylinder head gasket that has been damaged by the overheat!
One other lesson I learned was that the reservoir cap must be tightened down really well to maintain pressure. That might have been responsible for some of my problems, since a low pressure would allow water to boil and could produce vapour locks, and interfere with cooling.
Posted on Thursday 18th of August 2016Don't understand this? Ask a question