[Fullsize455]

Originally Posted by GT182

I don't understand why anyone uses diesel oil on their gas engines. It's for diesel engines not gas. I used it at one time in my 79 Formula and it ruined the engine bearings. That's one of the reasons I only use Valvoline. You might think your doing your engine a big favor but it the long run you aren't. And I've heard that from a number of retailers and those that have used it.

Sorry for the rant but I hojnestly found out the hard way.

All that sounds good to the totally uninformed who are unfamiliar with engine and fluid bearing design, but is of course totally false. Diesel oil did not ruin your bearings, nor has it ruined anyone else's.

Diesel engine bearings are no different than gasoline engine bearings, and oil intended for diesel engines is not fundamentally different than oil intended for gasoline engines. There are additive packages that differ somewhat, but they are absolutely interchangeable with no risk of damage. Now, using a high-zinc diesel oil in a modern car with a catalytic converters and sensitive O2 sensors may cause problems with those parts, but it will do no harm whatsoever to the engine itself.

Now, diesel oil is designed for the much harsher environment of a diesel crankcase, and is thus more robust. It also has to deal with more soot contamination and diesel fuel dilution than a gasoline engine oil. The additives and properties that result are beneficial in gasoline engines as well. Conventional diesel oils are not designed for prolonged high RPM, nor prolonged high temperature use, so something like Rotella T would not be suitable in any serious race engine that sees serious track time, but it is absolutely acceptable and in many ways better for everyday road usage.

Your anecdotal story of ruined bearings obviously neglects to mention some other serious factor that was the primary reason for your bearing failures, because the oil wasn't it. So long as you were using the proper viscosity oil of course, and changing it at proper intervals.

My own anecdotal evidence includes using Shell Rotella T 15-W40 extensively in numerous old carbureted pushrod engines over the years, including nearly 50k miles on the already high mileage 455 in my '71. I used nothing but Rotella T in that engine from the moment I acquired it with 193k on the clock. When I tore that engine down at 241k miles, it was still a good runner, had good oil pressure, bearings looked perfectly fine, and I have no doubt it would have continued to run for many tens of thousands more miles. Same goes for numerous other pushrod engines that I have used it in and have put tens of thousands of miles on. Never had any sign of trouble from any of them.

But of course, just like so many things in life, people love to fall back on their one-time singular piece of anecdotal evidence, having done no additional research on the subject, and present it as a definitive argument. Anyone that understands fluid bearing design and has some knowledge of automotive engine oils would never make such a foolish claim that "diesel oil ruined their bearings the one time I used it", because that is of course absurd.

So there, there's a counter-rant. I've been fighting the ridiculous myths about oil for years, but they persist because people love sticking to their anecdotes and blaming someone else, because it's easier than accepting reality sometimes.

[68 461 Bird]

Originally Posted by Fullsize455

Conventional diesel oils are not designed for prolonged high RPM,.

What do you consider prolong high RPM? On a long trip (3-5 hours) at 65 to 70 mph, my engine is at 3200 RPMs.

[Fullsize455]

Originally Posted by 68 461 Bird

What do you consider prolong high RPM? On a long trip (3-5 hours) at 65 to 70 mph, my engine is at 3200 RPMs.

That's fairly high for a diesel engine, but I wouldn't consider that high RPM. You can't ignore the context of my post, which was referencing race usage vs. street usage when talking about prolonged high RPM usage. 3200 RPM at a steady, low throttle cruise is not hard on an engine. Routinely giving it full throttle to redline is much, much harder on it, and diesel oil would not be approriate for that kind of abuse.

[68 461 Bird]

Originally Posted by Fullsize455

That's fairly high for a diesel engine, but I wouldn't consider that high RPM. You can't ignore the context of my post, which was referencing race usage vs. street usage when talking about prolonged high RPM usage. 3200 RPM at a steady, low throttle cruise is not hard on an engine. Routinely giving it full throttle to redline is much, much harder on it, and diesel oil would not be approriate for that kind of abuse.

Thank you for your reply and was not ignoring the context of your post. I was mainly asking your opinion if you thought a steady 3200 RPM was considered too high for the diesel oil on a street driven classic. I have been using the ZR1 Vavoline 20W-50 in my street driven classics, wasnt sure if I should switch over to diesel oil or not.

[TedRamAirII]

One issue is that "Rotella-CK" is not the Rotella that everyone's engine builder has used or recommended in the past. When it was rated CH, CI or CJ that's a entirely different oil than it is now, they dropped the "S" ratings, only the name is the same. Its all spelled out on the ratings on the side of the bottle. Reading the bottle of any motor oil, "APPROVED FOR" is different than "Recommended" or "Meets or Exceeds". So, if its safe for Cat Converters, it maybe isnt good enough for our Pontiacs. Every oil company has continued to remake and substitute their additive package to help auto/truck manufacturers meet emission specs. What is the latest, greatest oil....today?