1979 leyland Sherpa 230 1.7l with an "o series" engine.
I've an overheating problem for a while now and still trying to get to the bottom of it. The cooling system and heater matrix are all OK and the thermostat works.
First of all I did a power balance test and noticed the revs of the engine did not drop much on removing cylinder 1 spark plug where removing the others - there was a discernible loss of power. With the aid of a color tune I've discovered that No.1 cylinder is running leaner than the other 3. I can see that the flame is blue and won't get flecks of orange even if I richen the mixture. It would suggest an air leak of some sort but on spraying gaskets with propane I only get a 1% increase in revs. I personally think that's not enough of an leak to lean out the mix to that degree.?.
I'm starting to think internal air leak from inside engine like through valve guides or something but can't find any info confirming this will happen on Google. What do you think - any ideas?
As a leaner mix runs hotter and the said cylinder is the nearest 1 to both the thermostat and temperature sensor do you think that this could be enough to contribute to an overheating problem