I've been working on my 1980 242. No ac or power steering. I took it apart and cleaned intake manifold and painted it as well as valve cover. Has brand new alternator, engine wiring harness, timing belt, drive belts, tensioner,coolant temp sensor, water pump, thermostat, radiator, coolant hoses, all gaskets, seals, mounts, drive shaft, suspension, and exhaust. Basically everything but head gasket and fan clutch. But I did replace the metal fan with a known working plastic fan for easier removal in future. Finally started it up today and temp gauge slowly but surely went up about 80% just below the red and hung out there as it idled. Some slight fluctuation but definently above the middle "safe" zone. ny ideas on why it'd be running hot now? There's nothing left to replace! And it wasn't running hot before the tear down. Thanks for any tips.

 

Update. I replaced the thermostat incase first one was faulty. This did not help.

 

Did you do anything with the timing? Also the replacement fan may not be pulling enough air through the radiator. Is the radiator shroud in place. Also you may want to get the radiator tested for exhaust in the cooling system which would be a head gasket.

 

I had the timing belt replaced at a volvo shop before I tore everything apart. Fan shroud is in place. Do you think the plastic fan instead of metal would really do it? Mechanic suggested run it for a few minutes and turn it off over and over to get air bubbles out. It wasn't over heating before and compression was 155 to 170 so I assumed head gasket was ok.

 

It sounds like the only real thing that you changed was the fan. I would take to old fan and fan clutch and reinstall them. I assume you have the fan clutch installed with the plastic fan , correct? Just a general rule of thumb. If you ever change something and you run into a problem always go back to the parts you changed.