Article on using Diesel Engine Oil in your Gasoline Engine

[Stude Light]

I never, ever though I would post a new topic on engine oils as it has been discussed over and over in this forum. How many times can you beat a dead horse? But....I thought the article below interesting as I hadn't seen information on diesel oils before. Maybe it was already talked about here. If so, I missed it.

 

I have chimed in many conversations about oils, pre-war cars, post-war cars, ZDDP levels and how today's off the shelf oils are fine for all but the most severe application. My knowledge in this area doesn't come from anecdotal stories from the people peddling their specialty oils or additives. Instead, it comes from my discussions with the oil experts during my 30 years at GM, from reading the many SAE papers written on the subject at the time oil additive formulations were changing (I had access as a member), working with automotive & aircraft engine rebuilders and some other research I have done. But let's just put that discussion aside for now and focus on the pros and cons of using diesel oil in your gas engine cars.

 

All of my aforementioned research focused on gasoline engines and not on diesel engine oils. I have not done the research on diesel engine oils so I cannot make any definitive comments about the accuracy of the article. I am just sharing it for others to read and you can form your own opinions.

 

https://www.motortrend.com/how-to/diesel-oil-in-gasoline-engine/

 

 

 

 

[Grimy]

Thank you for this article @Stude Light.  The issues mentioned (engine speed, detergent/dispersant, types of ZDDP--all designed for low-speed engines) seem *just right* for our pre-war cars, especially the earlier ones.  For example, my 1918 Pierce has a 2500 rpm redline and never sees above 1700 rpm; the 1925 with a 3000 rpm redline never sees above 2200 rpm, and the 8-cyl engines with peak hp at 3400 rpm never see above 2700 rpm.  I've been using Rotella in my fleet of old iron, and my F350 diesel, for years.

[Rusty_OToole]

Interesting article if you have a race car but I don't see the application to vintage models. Would like to see your thoughts on oil for cars from the sixties and older.

[Stude Light]

45 minutes ago, Rusty_OToole said:

Interesting article if you have a race car but I don't see the application to vintage models. Would like to see your thoughts on oil for cars from the sixties and older.

I didn't really want the post to get into this discussion but you asked.....

 

For most of my cars, whatever is on sale. I generally follow the OEM recommendations for viscosity. Most modern cars that I plan to hang on to, I stick with synthetics. Synthetics are really good oils but on my more vintage cars, I just don't put that many miles on them and like to change oil after the summer season before they sit for the winter so I just use mineral oils. Synthetics would be even better but the benefit vs cost curve is too flat for me. 

 

My 1968 Pontiac Tempest 350, 2 bbl, 2 speed automatic - off the shelf 10W30

If I still had my 1967 GTO, which had a higher lift cam, stronger aftermarket springs and higher compression (and I beat on it) - I would use Valvoline VR1 or equivalent with a bit higher ZDDP.

 

I still volunteer at the RE Olds Museum and am exposed to a variety of years of cars that get driven. In general 1920s-1950s, I recommend using off the shelf oils and pick the weight on age and season. That stuff has plenty of zinc and phosphorus for all the flat tappet engines including the 303 four barrel Rocket Engine in the 1953 NASCAR they have or the 394 in their 1959 Super 88 convertible. 10W30 is a good all around oil. The really early stuff with a total loss system, I typically use SAE30. Also use SAE30 oil in some of the later cars, like their 1937 Olds Straight 8.

 

I used to run SAE 30 in my 1939 LaSalle but I think I am going to run 20W50 in the future. That heavier weight keeps the oil pressure up a bit higher when hot and idling with that V8.

 

There has been so much misinformation on ZDDP levels for a number of years that many people now think that any old car needs a specialty oil or an additive. When they reduced, not removed, the zinc and phosphorus in the oil additive package to help with catalytic converter life, the SAE worked to ensure the levels were still adequate to protect the high contact pressure areas for all the stuff still on the road. They did suggest that engines with with higher than normal contact pressures at the tappet to cam (race engines with high lift, increased spring pressures, high compression ratio, and high rpm) would want to stay with the higher levels of ZDDP. So, folks that "build" performance engines and those that race might want to run something like VR1. Increasing the zinc and phosphorus a bit higher than recommended caused pitting and spalling on various bearing surfaces so too much is a bad thing too, thus I don't recommend additives as there is no way for you to know the levels are within the tolerable range.

 

If you choose to pay a premium price for a specialty oil, that's fine. It isn't going to hurt your car, only your pocket book but it is not needed for the 90% of us that aren't performance car owners and definitely not needed for any pre-war car owner. From the article, the diesel oils might not be a good choice for the performance car enthusiast but shouldn't have negative effects for lower rpm engines That's my two cents on the subject.

Scott

 

 

 

[Rusty_OToole]

I got a valuable lesson in oil when I watched a movie of the 1933 Pierce Arrow 24 hour Bonneville speed record. A stripped stock Pierce V12 averaged 117 mph for 24 hours which was astonishing for the time, especially for Pierce which was not considered a fast or sporty car. And they did it on Pennzoil 20W20 oil.

This proved to me, that thirties cars even with poured babbit bearings did not need heavy oil. I have also seen old articles that said heavy oil causes more wear on startup when cold because it takes so long for it to get to where it needs to go. Most old cars, if you look at the manufacturer's recommendation, only called for 30 weight oil in hot summer weather.

I also know that 10W30 was available from 1951 or 52 on, and detergent oil from 1947. 10W30 detergent oil, was the default choice at every service station and dealership from the fifties thru the eighties.

Zinc was not used until about 1951. The new OHV V8s of the time suffered from cam and lifter wear that required improved lubricants, and in some cases, different material for the cam and lifters. Previous engines did not have this problem, flatheads have much lighter valve trains and valve springs, and the low revving OHV engines likewise, did not stress the valve train as much as the new high revving short stroke V8s.

So, my opinion is to use a good name brand 10W30 in postwar cars. Zinc not necessary unless it is a highly stressed pushrod OHV performance engine. Prewar cars, most likely the same, if they are clean inside. In any case use the lightest oil recommended by the factory.

Synthetic oil probably not a good idea because it can creep thru seals and gaskets where regular oil won't. I would use it in a newly rebuilt engine with modern seals and gaskets but not otherwise.

Would like to know if this fits in with your ideas.

[Stude Light]

5 hours ago, Rusty_OToole said:

Would like to know if this fits in with your ideas.

If you are asking me....I agree with you. I will add a couple of things. I made the assumption that people don't drive their antique cars in the winter, at least not in my home state of Michigan. So, I based the oil viscosity on my summer driving and that you take the time to warm the engine up a bit before any hard or higher speed driving.

 

The early synthetic oils were ester based  and quality control wasn't that good so the higher ester concentration would swell seals and cause leaks. The modern synthetics do not have those issues and a lot of work was done to ensure compatibility with the various oil seal compounds (nitrile, viton, etc.) I would have no issues putting synthetic in any of my older cars. Well, my Studebaker and Olds don't have any seals anyway!

 

I didn't get into the AD (ashless dispersant or detergent, as many call it) discussion. That's really the only oil to use. AD oil just keeps things in suspension better, especially carbon, so it can be filtered out. Who wants oil that settles everything out in the bottom of their pan? If you don't have a filter then change the oil more often. I do recommend dropping the pan on any engine with unknown history.