View Full Version : Diesel Oils in Gas Engines?
Mike.Bray
06-10-2025, 05:12 PM
This could be a get the popcorn thread, especially with all of the "I've been running Rotella oils for 150 years with no problems" comments. You have to say that with a crusty old man voice. Anyway, Lake Speed Jr. worked for Comp and Driven and probably knows as much about motor oils as anyone so when he speaks it's not a bad idea to listen.
Lake has an entire YouTube channel about motor oils, here's a good video where he digs into the science of gas and diesel oils and how they affect engines. Take from it what you like.
https://youtu.be/HcJHJL5Ys-Y?si=S-vs4gqFsZgFCyIr
tnt_motorsports
06-10-2025, 07:08 PM
Like everything, there are all kinds of opinions, but here is mine...
I run HDEO in all my OPE and have for several years now. I have run 10w30 and 15w40 viscosities. I intend to run either of those same viscosities in my engine when it is completed. It will be a non emissions SBF so HDEO won't be a problem.
The real concern comes in with modern day oils and the additive package affecting the emissions systems. This is the biggest reason for the lack of dual rated oils these days. The other big factor is the thinner viscosities to help meet the mandated EPA MPG requirements.
Our boats ran 15w/40 diesel oil in their 5.7 Vortecs per manufacturer specs.
jts359
06-10-2025, 07:36 PM
We run Rotella 15-40 in our boat 5.7 engines also. I have for years , Ed
rponfick
06-10-2025, 08:13 PM
Let the fun begin.
TrackDay17
06-10-2025, 08:33 PM
Until I watched his channel I didn't know what a tribologist was.
ggunter
06-11-2025, 07:46 AM
Well... until I watched Lake Speed Jr's You Tube video on why diesel oils can be detrimental to a gas engine, because the calcium in the additive package is higher (due to the soot diesel engines put out) can fight with the zink in the additive package and cause premature wear. He equates the calcium to a paint scraper that scrapes off the zink coating and causes wear. His oil analysis showed this to be true. I always thought Diesel oils were superior especially in high horsepower applications. I used them in my boats forever. I ran a 2003 Nissan Sentra on nothing but 15w40 diesel oil out to 312000 miles till the trans made a noise the radio wouldn't cover up. The next car was a 2010 Impala with 306000 miles till that trans went. My current Impala 2015 with the 3.6 engine (still has the original timing chains that they are known for stretching and causing issues) and still driving it, has 326000. All of these cars have had a steady diet of 15w40 diesel oil. All were changed at 5000 mile intervals religiously. So, if diesel oils are bad for gas engines I'm still waiting for the results. OBTW. I run 15w40 in my Cobra too.
rich grsc
06-11-2025, 09:50 AM
He makes his money buy making YouTube video's. The more controversy the more views. Diesel engines don't last many hundreds of thousands of miles with poor oil, and change intervals of up to 20,000 miles. It says right on the packaging of the oil---"meets or excess all specification for internal combustion gas engines". Your $$$$ use what you want, but I've used 15w40 for over 55 yrs, never had an oil related failure. Look and see how many engine failures that can be linked to the use of diesel oil. The oil gets changed so frequently in these cars, you could use the cheapest re-refined oil and be fine.
Interesting video.
He didn't say that diesel oil was 'poor oil', he said it had detergents in it to handle soot that were not needed for gas engines and can counteract the effects of the increased quantity of ZDDPT. Obviously a lot of people use Rotella in gas cars and haven't noticed adverse side effects, but I think he's showing how diesel oil isn't better or worse oil...just different oil and may not be the best for regular gas engines. Makes sense to me.
Mike.Bray
06-11-2025, 02:35 PM
Interesting video.
He didn't say that diesel oil was 'poor oil', he said it had detergents in it to handle soot that were not needed for gas engines and can counteract the effects of the increased quantity of ZDDPT. Obviously a lot of people use Rotella in gas cars and haven't noticed adverse side effects, but I think he's showing how diesel oil isn't better or worse oil...just different oil and may not be the best for regular gas engines. Makes sense to me.
Yeah the science is the science isn't it? The other side of this is most street engines having roller cams these days. I suspect running diesel oils in an engine with a flat tappet cam would not be a great idea with the zinc being neutralized. Of course a flat tappet cam in general is not a great idea these days but that's another topic (cue up the crusty old man again with his "I've been running flat tappet cams since the 1800's and never had a problem!)
I've mentioned before a good friend of mine is the operations manager for Classic Recreations/Shelby Garage and he used to work with Lake at Comp. They traveled together a lot so he got to know him very well. Lake lives, breathes, and eats motor oil, he is the real deal and works with the science. And keeps up, today's oils aren't the same as even 10 years ago let alone 40 years ago. I always thought Mobil 1 was THE oil, and it was, but not anymore. It's a shadow ot its former self.
jts359
06-11-2025, 09:02 PM
I know the amount of zddpt has been decreased in Rotella so why would they put something in the oil to counter act it ? Ed
GoDadGo
06-11-2025, 09:10 PM
I run Rotella T5 15W-40 in my Zero Turn, Push Mower & Pressure Washer and have for many, many years. In the Cobra I run Rotella T5 10W-30 and change the oil in the spring and fall and it always looks clean. All are carbureted and this is the main reason why I used the Rotella because of the detergents.
While I don't know if this is a good idea or bad, I ran the Rotella 15W-40 in my 1980 Z/28 from the time it was new until 2005. I rebuilt that engine twice, basically doing simple refreshes and camshaft upgrades, and I never had to bore it because the worst cylinder taper was under .010". That car saw a lot of miles in it's lifetime and I credit the Rotella for keeping it running well until Hurricane Katrina got it.
In our modern vehicles, 2018 Ram, 2022 Challenger and 2023 Durango I used Mobile One Extended Performance and change it at 5000 mile or lower mileage intervals. In my son's old car, which is now 25 years old, I use Mobile One Extended Performance high mileage.
That old project car can be seen in the YOUTUBE link below:
https://youtu.be/jDd9F58WIEE
StangRacer
06-11-2025, 09:33 PM
and I never had to bore it because the worst cylinder taper was under .010".
Is that a "typo"? .010? Out of curiosity, what was the taper?
GoDadGo
06-11-2025, 09:51 PM
Is that a "typo"? .010? Out of curiosity, what was the taper?
The worst cylinder had bore tapers were between 4.006" and 4.009" so I honed them and slapped it back together with new rings and bearings.
For the the second refresh I changed the heads from the 76-CC original smog heads to a set of 64-CC Dart Iron Heads with 200-CC Runners.
Also, the engine and transmission that resides in the Redbone Roadster was supposed go in my 1980 Z/28 that went swimming in 2005.
StangRacer
06-11-2025, 10:02 PM
The worst cylinder had a bore tapers were between 4.006" and 4.009" so I honed them and slapped it back together with new rings and bearings.
For the the second refresh I changed the heads from the 76-CC original smog heads to a set of 64-CC Dart Iron Heads with 200-CC Runners.
Also, the engine and transmission that reside in the Redbone Roadster was supposed go in my 1980 Z/28 that went swimming in 2005.
Gotcha... Sometimes doing those quick rebuilds can result in decent running engines.
Sorry to hear about Z. I went to school in New Orleans, well before Katrina, and went back for a visit in 2017. It was crazy seeing some of the buildings and houses still in disrepair.
Blitzboy54
06-12-2025, 11:34 AM
I ran diesel oil on all my race bikes. High RPM relatively low heat. I never had a problem but that doesn't mean it was the right thing to do.
Ford & Jeep Fan
06-12-2025, 01:21 PM
I think the target audience for the this video the owners of modern direct injection gas cars.
After spending a some time watching some of their other videos, I have confirmed one of my long held beliefs that SYNTHETIC oils ARE NOT FOR BREAK IN
Mike.Bray
06-12-2025, 03:14 PM
After spending a some time watching some of their other videos, I have confirmed one of my long held beliefs that SYNTHETIC oils ARE NOT FOR BREAK IN
There is zero doubt synthetic oils are not for break in.
Ford & Jeep Fan
06-12-2025, 04:09 PM
There is zero doubt synthetic oils are not for break in.
I agree.
I did a quick search on ebay to see what was out there, and there it was,..... "Royal Purple Syn break in oil. "
I think some brands are Maybe Equal but no better than the mainstream but live on the hype Thus Command their "Royal Prices"
Mike.Bray
06-12-2025, 04:18 PM
I agree.
I did a quick search on ebay to see what was out there, and there it was,..... "Royal Purple Syn break in oil. "
I think some brands are Maybe Equal but no better than the mainstream but live on the hype Thus Command their "Royal Prices"
This is what I use. https://www.summitracing.com/parts/cca-1590 https://www.summitracing.com/parts/cca-159
After that it's Driven oils. The actual good stuff.
GoDadGo
06-12-2025, 06:01 PM
This is what I use. https://www.summitracing.com/parts/cca-1590 https://www.summitracing.com/parts/cca-159
Ditto On The Comp Cams Break In Oil Mr. Bray!
https://youtu.be/I86I7a_x9W0