I'm going to change oil for the first time and was curious what type oil I should use . I have an 1985 Royal 88 with a 307 with 81k. I have documents of all oil changes and none of them have oil weight on there so wanted to know if anyone out there can help me out. Thanks

 

Oil weight depends partly upon the seasonal temperatures in your area. You don't have a location in your signature so it's unknown if you are in a -30F or +100F region.

 

Usually it's 10W30 winter / 10W40 summer. If the engine is worn, 20W50 may be better in the summer.

I have no idea what the '85 recommendations are, but it should say in your owner's manual.

- Eric

 

10w-30 should be fine for a 307 with 81k under its belt, unless you get hard winters, then I'd say 5w-30 would be better. Don't forget oil has to get round the engine asap on startup, and carries heat away from the bearings, if your oil is too thick it won't do this very well, if it's too thin it won't form a film to ride the bearing surfaces.
10w-30 is what the engine is designed to work with according to my '82 Cutlass Supreme shop manual.


Roger.