Choosing the Proper Oil for Your Imperial


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From Dick:

I'll once again mention Skinned Knuckles magazine for those of us who are very interested in good care for our old cars.


SK just did a very good article on the oil problem in the September 2007 issue, which basically is a result of the EPA rules regarding contamination of catalytic converters; because of those rules, modern gas engine oils have had the ZDDP (zinc) additive reduced to less than 1/100 what it was in the heyday of our cars' youth, resulting in very poor protection against startup wear for cars that are not driven every day.

As a result, it is important to switch to oils which DO contain the Zinc anti-wear additive, which are only available for engines that do not require catalytic converters, which of course are diesel engines.

So, folks, next time you change your oil (and make it soon, please), buy diesel rated oil; do NOT continue to use SK, SL or SM rated gas engine oils.


Look for any oil with a "CX" rating - where "X" can be any letter - the "C" stands for "compression ignition".

Some older stocks will be labeled something like "SG-CD", "S" meaning spark ignition, "G" meaning 7th edition of SAE spec, "C" meaning compression ignition (Diesel), and "D" meaning 4th edition of SAE spec. All name brand oils have this lettering on the container somewhere - just search until you find it.

Current production gas engine oils no longer have the "CX" rating, because they have had to leave out the ZDDP wear reduction additive that is needed in engines that are seldom used, (which is a common situation for heavy equipment - meaning most Diesel engines until recently).

Diesel rated oils have always been the best choice, in my opinion, because they have always had superior detergent properties, and are top notch in all other respects. Until this recent change, I used the Chevron RPM-DELO "400" SAE30W Diesel rated oil in all my gas engine cars, but that is getting very hard to find these days anywhere but a Chevron distributor. Also, it is no longer rated for use in gas engine cars because of the catalytic converter problem (of course this does not apply to cars built before 1975 or so.)

The oil I now use is 15W-40 Chevron RPM-DELO "400", because that is the brand I have always used, and because that specific grade of oil is required for my new Diesel truck - so I just buy it in case lots for all my vehicles now. I'm sure all the major oil sellers have an equivalent.

As for a subscription to Skinned Knuckles, you can go to and then click "PayPal" or you can send payment to them at PO Box 6983, Huntington Beach, CA 92615-6983. The check or money order must be in US funds, and drawn on a US bank. The subscription cost is $24 per year.

Dick Benjamin

This page last updated October 31, 2007.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club