Everyone always said "10W-40" as the default response for that car. Can 0W-40 be anything (significantly) different other than it's viscosity at cold temps? I think of 10W-40 and 10W-30 (which I've used occasionally in the past as well) as identical at cold temperatures. Speaking of temperature, about how hot DOES this kid of car run? Everyone talks about cars "running hot" these days. Is this relative? Did cars "run hot" back then? This is a 500 CI motor after all. I just don't know.
I've used 15W-50 Mobil-1 synthetic and other grades of conventional oil (10W-30 up to 20W-50) before. None produced any ill effects that I can report. The engine does leak oil to a degree and none of those oils made it better (or worse). My real question is would 0W-40 make for easier starts in the cold? I want to make the engine last (never have to rebuild or replace) so synthetic is an option I'm thinking of returning to, and perhaps
0W-40 is the right grade for every situation. But if people have other ideas, I'm always listening.
I have found the posts so far very imformative: a big thanks to N8N, KRP and Ad absurdum per aspera.
Having had one of those glorious beasts Eldorado with the 500. . . I can say they are particularly delicate motors. It was not one of GM's better offerings. Neither was the pain on the Eldos, particularly the metallic. I think the engine would do okay today if you had a new one and stuck with oil like Castrol Edge. For some INSANE reason, it seemed like many people used Pennzoil and Quaker State in those engines. By the time they had 50,000 miles they were full of sludge. Cylinder walls horribly varnished and scored. They were blowing oil like mad by 65,000 miles. Seems like people with other GM vehicles were not as prone to use that crappy Pennsylvania oil. Don't switch. Use a major brand conventional oil. Like I said Texaco and Shell have really good, inexpensive oils as does Union 76 and Phillips. Stay away from the off brands and chain store oils. (K-Mart - Wal Mart etc) House brands. Castrol makes really good oils too.
The 500 isn't a bad engine if you care for it properly. Like I said, if you got a new 500 it probably would hold up well. GM engines of 1970 generally weren't the best. That was a dark period for American cars in general.The bad American cars of the 70's is why you see so many Japanese cars today on our roads. Detroit was largely building "shit." The engines had all that emissions crap on them that really didn't work well and burned valves etc. Rube Goldberg devises thought up by Ralph Nader types who had NO idea what makes an automobile run. That is another reason Japan & Company got 55% of the American car market. Japanese cars didn't have to have all that crap sucking the life out of their motors.