Engine Grade of Oil

[Tom Douglas]

I have a 1941 Cadillac Coupe Series 62 with a Flathead V8 engine.  My MoToRs AUTO REPAIR MANUAL says: Above +32F 20W, Above +10F 20W, and Above -10F 10W.  Is this what those of you who are familier with this vehicle follow for the Grades of Engine oil?

[Bill Ingler CLC# 7799]

Tom  - I live in Scottsdale and both my 41 and 47 use a straight 30w as most of my driving is done with driving temps in the higher range since we live and do a lot of driving in Arizona. When I lived in Ohio I used 10w30. I think most who have flatheads will tell you a 10w-30 is a good weight oil for your car.

[Gary Phillips]

Just curious, do you have a Hydro matic transmission in your 41.   If so, please see my posted question.  Thanks.

Gary

[Mike #19861]

 My recommendation would be to use Rotella T 15W40 oil. This is an oil normally used in HD diesel trucks. I have been using this grade of oil in all my cars for some 25 years with very satisfactory results.

 I would have to assume, that this engine is relatively free of the sludges that were normally built up in the old days from the single viscosity non-detegent oils. If not, the high detergents and ZDF in these oils may dislodge some of the sludge and cause it to plug the oil passages causing severe engine damage.

 But, the 15W40 oils are perfectly suited for these engines. The old 30W oils cannot compare. These oils were recommended in the days before mutli-viscosity detergent oils became available and were a good oil for their day. Since, lubrication technologies have eclipsed these oils. I would use the best that is availble for your engine and not follow the 60 year old recommendations the period manuals give.

  Mike