Diesel Oils in Gas Engines

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Sorry to open up this can, but I think it’s worth considering the additive packages in the oils that we’re using in our Pierces. The last crankcase fill before I assumed caretaker-ship of the Model B was some late-70s Kendall 30-weight that had more in common with a 40-weight, according to the Blackstone oil analysis that I received. Predictably, the anti-wear and dispersant additives were next to nothing. Of course, I hadn’t run the engine at that point, but still did a cold drain before removing/cleaning the oil pan and disassembling and cleaning the oil pump/checking clearances.

Although Pierce spec’d a 30-weight for summer, and 20 for winter, I’ve decided to use a multi-vis of the fully synthetic type. The crankcase was very clean when I dropped the pan, and the underside of the pistons didn’t even have the typical coffee color of an engine that’d been run for a time (owing to an earlier overhaul before being parked for about 40 years). I poured Valvoline 5W-30 into the crankcase for the first few garage runs. To give the engine its oil due, I also added some two-stroke oil to the non-ethanol gas. Now that it’s back on the road, I’m adding a little Marvel’s Mystery Oil to the fuel to add some lubricity for the valves.

After the first few road trips, I did some frequent oil changes and added Valvoline 10W-30, and then Rotella 15W-40. With the engine fully warmed up, the oil pressure is 12-15 psi at idle, and about 28-30 psi at 45 mph. This is consistent with the RADCO manual thresholds for pressure. At this point I’ve moved over to Mobil Delvac Extreme Duty 15W-40, which I will likely continue to run. Such frequent oil changes could be seen as wasteful, but this car doesn’t have a disposable oil filter unit on the block, and I consider it important to keep circulating fresh oil to promote gradual cleaning.

Every engine is different, but the wear materials are something that I watch through drain samples and oil analysis results. From the AACA, I came across an article by Bob Olree of GM’s Powertrain Fuels and Lubricants Group, and he has some interesting commentaries on a host of oil concerns. Taking this is step further, I’ve been following Lake Speed, Jr.’s assessments of oil, based on his own tribology work for SPEEDiagnostix. His address of various oil concerns and applications is very insightful, and I think worth your time.

Speed Jr.’s research and data suggests that the higher calcium and dispersant contents in some diesel oils can displace the phosphorus and zinc anti-wear additives, and potentially cause more wear issues in gasoline engines, particularly in the valve-train. Based on this research, I think it’s wise to verify the additive package numbers, and particularly excessive amounts of calcium in some oils before deciding to pour them into the crankcase, only with the consideration that more zinc is a good thing. The adage, “a little is good, a lot is better, and too much is just right” should not apply to the zinc matter, as with an overabundance it can actually fatigue metal/reciprocal components. As well, too much calcium can cause accelerated wear on cam lobes and tappets.

What I gather from Speed Jr.’s analysis is that no matter the oil that you choose, take time to consider what the balance of these additives is doing, as they may be the opposite of your intents for that irreplaceable classic.

 

Why DIESEL Oil is Actually WORSE for Gas Engines!

https://www.youtube.com/watch?v=HcJHJL5Ys-Y

 

 

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