Hot Rods What oil should I be running in my flathead?

Zddp additive is unnecessary if your engine is stock. Flatheads never had zinc in their years of manufacture, why should they now? The valve spring pressures in a stock flathead cause no problems. However, if I was running high pressure valve springs and an aftermarket cam (which is most likely been ground on a soft chinese cast billet) I would definitely use it. Zddp was only added to oil in the early 50s when the new-fangled OHV V8s Olds and Caddys with high pressure valve springs started eating their cams.

 

I'd throw some Rotella in there.

 

Flathead what? Multigrade oil was introduced in 1951, detergent oil a few years earlier. 10W30 detergent oil was the default choice in every gas station and dealership in the fifties, sixties and seventies. Chances are your postwar car hasn't used anything else for the last 60 years.

The advice to take off the pan and clean out the sludge is good. If you can't do that, and the oil seems to get dirty quick, then 2 or 3 oil changes in rapid succession will help clean it up.

I don't believe in any engine cleaner or sludge dissolver. Have seen it release large amounts of sludge and damage a motor but have not had trouble with detergent oil.

If you are talking about a motor from the twenties or thirties that has never been rebuilt or opened up it could be a different story.