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engine oil for 1941 De Soto


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There has been lots of discussion on this subject, and this is just one opinion from an old car enthusiast:

Personally, I use 30wt or 10w-30wt non-detergent oils in my prewar cars that do not have oil filters. Detergents & associated additives scrub and hold particulate in suspension so it can be removed by filters;...no filter...no detergents needed. Older engines were designed for non-detergent oils that allow the particulate to drop out in the pan. Regular oil changes and periodic cleaning of sludge from the oil pan was the standard method of removing dirt from old engines.

The one potential problem with modern oils is the relatively recent removal of zinc additives to prolong catalytic converter life in modern cars. Oils without zinc have been documented to increase wear on camshafts and pushrod bearings.

If your car has roller bearings running on the camshaft, you are probably OK using oils without zinc. Otherwise, you can use oils formulated for diesel engines that still have the zinc additives.

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I agree for pretty much the same reasons.

Also, if an engine has been using non-detergent oil for any length of time there's particulates in places with close tolerances. put a detergent oil in there and it'll clean all that out and open up those tolerances, which can cause serious problems.

I also believe though that if you have an engine that has been using detergent oils, regardless of when it was made, it is safe to continue to use it. I would be careful about the sinc thing though.

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Guest Bob Call

If you are concerned about cam and lifter wear because of low or no zinc in the oil, use a zinc additive. Even modern, since 2004 API Service CI and CJ, diesel oil has very low zinc content so is not suitable for flat tappet engines. Since the late 80's virtually all cars and trucks have roller valve lifters so the lack of zinc is not a problem for them.

Gasoline engine API Service SH, SJ, SL and SM oils have little to no zinc. What you need for your old flat tappet engine is API Service SF or prior. I believe WalMart still has a house brand that is rated SF. If you can't find SF, I would suggest using a zinc additive as insurance.

Here is a link to an oil service catagory chart.


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