Springtime Oil Delima

[Alan T.]

Duke, a question...

don't laugh, I know its a pretty silly question...but if I've been using an oil like Penn 10W-30 for years in an older engine and now start using one of the "diesel" oils in it, is there any problem with that? I can't imagine there would be, but in a valuable engine I don't want to take anything for granted when making a change from what its used to.

[Duke W.]

Re: Duke, a question...

Lubricating oils for both gasoline and diesel engines have evolved over time as evidenced by evolution of the API service specifications.

Go back 10 or more years and most motor oils were dual rated - such as SE/CD back in the seventies. These oils met BOTH then current spark ignition AND diesel engine specifications and qualification tests.

Understand that motor oils are blended for CURRENT new engine requirements, and the OEMs have agreed to a reduction in the ZDDP antiwear additive due to current engines having "roller everthing" and the concern that phosphorous combustion byproducts of ZDDP may degrade catalysts, which places OEMs at risk with 100K miles emission system warranties.

For the first time ever the current SM spec actually places a LIMIT on phosphorous concentration, which limits the amount of ZDDP that the oil can contain to about HALF the concentration of CI-4.

The base stocks of diesel and spark ignition oils are essentially the same and many have some synthetic components added to meet the current tough oxidation requirements for both classifications.

Despite whatever BS is promulgated by oil marketers, there are NO current oils that are specifically formulated for vintage engines. Any oil that is labeled SM is for CURRENT new engines/emission control systems, and ZDDP is limited.

The basic question is what available oils are best suited to vintage engine requirements? CI-4 is best because of its richer additive package including a higher concentration of ZDDP compared to SM. CJ-4 also limits ZDDP, but not as much as SM.

So it comes down to selecting a suitable currently available API specification, not BRAND, and a suitable viscosity range based on the lowest typical starting temperature.

API CI-4 or CJ-4 has an additive package that is more suitable for vintage engines that have mostly sliding surfaces in the valvetrain, and SAE 15W-40 is suitable for cold starts down to about 10F and ambinet temperature operation to 100+ F, which probably covers about 99.99 percent of vintage engine starting and operating environments since most vintage car owners dont' start them in sub-zero weather.

So the short answer is that your vintage engine is more likely to sustain damage from using SM than CI-4 or CJ-4, and CI-4 or CJ-4 is more likely to protect your vintage engine from any damage than SM.

Duke

[Brad B.]

Re: Duke, a question...

Ive gone thru the archives and extensive conversation with some race guys, I still have a choice of very different oils and filters for my fresh 427 solid lifter engine. Either the Rotella 10-40 diesel c1-4 with a wix or ac filter, or Mobil 1 synthetic 15-50 with a mobil 1-111 filter. Any votes out there?

[Joel Falk]

Re: Duke, a question...

Rotella with a Wix filter would be my choice.