I have a 1980 F150 with a straight 6 in it. It has 111,000 miles on it. My dad bought it brand new in 80 and kept it in nice condition. I bought it about 5 months back. Lately, my engine has been overheating. There looks to be oil or oil residue on the side of the block over the spark plugs. But there is plenty of oil in the engine itself. Can anyone please enlighten?

 

Oil over spark plugs is probably a valve cover gasket going bad, and most likely isnt related to the problem.

I'd try to change the thermostat. They are about $6.00 for your truck. Sometimes they go bad and won't let enough coolant into the engine, which causes them to overheat.

 

Take a look at the radiator cap. I purchased my 89 a few months ago and the prior owner had replaced a bunch of cooling system parts, based on receipts in the glove box, but the radiator cap was original and the seal on it was way past worn out and needing replacement. This is an easy part to check.