Most probably a loose tappet. Check the valve clearances. Or a valve could be sticking in its guide.If the lifters are hydraulic (unlikely on older cars) they might be gummed up. A good flushing oil will clear sticking valve and lifter problems.
drivers side footwell behind panel by bonnet release lever drivers side footwell behind panel by bonnet release lever
warning lights on dash mean something is wrong u would have a generator light a temp , and an oil light
rule of thumb on cars after 1970. heat rises(water coming out top of engine is hot). so disconnect the top and bottom hose from the engine and let the coolant run out (either into a container or into the gutter) the put a garden hose on full up to the top (not the cap) of the radiator and run through the whole thing for about two minutes. then put on the bottom and repeat. then reconnect the bottom hose and run through the top (not the cap) of the radiator so that water passes through the radiator and the block (engine) for about 10 minutes, or about 3 minutes after the engine reaches running temperature. when done with a quality radiator flush product the radiator clean enough for a coolant change.