Proper oil for original 289

[65convertible]

I was going to go with 10W-40 Castrol high mileage oil

However, the last post looks interesting. The only thing that I can find Amsoil 15W-40 in is a synthetic blend for diesel. Would this blend of Amsoil be okay?

 

[Ed]

All of the suggestions so far are good ones. 15W45 seems ideal.
As an experiment which also might double as a mild and safe engine flush you might want to run some of the lightest stuff available for a 1000 miles or so. 5W-20 or 0w30 just to see if there are any potential leaks, serious degradation in oil pressure or consumption. I tried this with my 79 Toyota when it had 100000 miles on it and noticed only a slight incease in idle speed and gas mileage. This sort of proved that I had been doing something right so I went back to my tried and proven 50/50 mix of castrol GTX 10W30 and 20W50.

 

[k1xv]

"High mileage" oils, as I understand it, contain additives intended to swell seals to cut down on oil consumption (and maybe leakage?) in high mileage engines. It does not sound like you have that problem, and I would be afraid of anything that is intended to have any effect on apparently functioning seals that may be up to 40 years old if original.

Similarly, while synthetics today also are supposed to have no negative effects on seals, who knows if that statement holds for 40 year old seals from the mid - 1960s? Probably does, but why take a chance?

Engines in those days typically used 10-30 or 10-40. Of what is readily available today, affordable, undisputably good/high quality, I don't think you can go wrong with one of the 15w-40 fleet/diesel oils at WalMart, such as Mobil Delvac 1300, Chevron Delo 400 or Shell Rotella. You have no catalyst to worry about, and these oils meet current SL standards anyway. Any of them is superior to the oils available back in 1965.

 

[65convertible]

Thanks everybody for the nice replies. I think I will go with one of the 15W-40 oils.

You all gave me plenty to think about.