Nothing really wrong with using Rotella in a gas engine, either old or modern. An engine is really just an engine.
Rotella T-4 has the following API specifications: CK-4, CJ-4, CI-4 Plus, CI-4, CH-4, SN. The SN is the gas engine approval, so anything with an S_ approval could be used in an old engine. Yes, ZDDP has been reduced in the last few years in ALL the diesel oils, and likely in gas engine approved oils as well. [on edit] attached is a snip of oil analysis results on my diesel truck using conventional 15W-40 oil. You can see that the reduction happened around 2018.
That being said, I plan on using VR-1 oil in my engine, which supposedly has higher ZDDP than the "normal" gas engine oils you'd find on the shelf at Walmart or wherever.
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Last edited by klhansen; 11/08/2025 9:51 PM. Reason: added picture
Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.