your OWNERS MANUAL will tell you' if you can read, that 5W30 is the required viscosity for the engine
separate a timing connector on the firewall in engine bay which allows you to time the engine,then adjust the distributor.The connector is on the drivers side below the cowl and when separated the engine will run differently.
Engines used during that time used raised-rail heads and a one piece rear main seal.
labor time to replace engine in a 1984 chevy c60
Will it fit? No it will not fit, but that does not mean it cannot be done. With some serious modifications and I do mean serious mods, lots of money, time, and skill it is possible.
Next time, use Locktite or something similar to hold the bolts and/or nuts in place.
Factory says 5W30 in winter time. And 10W30 in the summer time. If you use heaver oil, The little roller bearings in the valve train will not lube. And it will take the valve train out. severe engine damage
It may be time for a tune up.
Spark Plug wires connected incorrectly, or engine is out of time.Spark Plug wires connected incorrectly, or engine is out of time.
oil building up on the pistons-the rings are bad
If you have enough time and money you can... but why?
Probably in need of a complete tune up.
If it is stuck closed, the engine will overheat. If it is stuck open, the engine will take a long time to reach operating temp.