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diesel engine oil in a gas engine?

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Old 19 Feb 2021, 02:35 pm
Cool Cruiser
Join Date: Jul 2016
Location: east central wisconsin
Posts: 244
Default diesel engine oil in a gas engine?

I've heard it's ok to use diesel engine oil in a gas engine but not gas engine oil in a diesel. Got a really good deal on some Mystik JT-8 15w-40. I do have a couple diesels. I would like to use it in my cars too. Been using diesel oil in my motorcycle for a decade. What do you think?
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Last edited by circus; 19 Feb 2021 at 04:14 pm. Reason: deleted a couple yes's
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Old 20 Feb 2021, 02:51 pm
Handy_Cruiser's Avatar
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Join Date: Oct 2013
Location: Arkansas
Posts: 10,782
Default Re: diesel engine oil in a gas engine?

In many cases, the motor oil designed for diesel engines has the wrong type and amount of detergent in it. Diesel engine oil has more additives per volume. The most prevalent are over-base detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to deal with them. When you put this extra additive load in a gasoline engine, the effects can be devastating to performance. The detergent will work as it is designed and try to clean the cylinder walls. This can have an adverse effect on the seal between the rings and liner, resulting in lost compression and efficiency.

Besides all of this, some of the byproducts of combustion (lead, zinc and phosphorus) can severely cripple the catalytic converter’s ability to perform this job. Diesel engine oils have a higher anti-wear (AW) load in the form of zinc dialkyldithiophosphate (ZDDP). The catalytic converters in diesel systems are designed to be able to deal with this problem, while the gasoline systems are not. This is one of the main reasons you don’t want to use a diesel engine oil in your gasoline engine. If your automobile was built prior to 1975, there is a good chance it does not have a catalytic converter, and thus the above statements do not apply.

So how do you know if an oil has been designed for gasoline or diesel engines? When reading a label, look for the API (American Petroleum Institute) doughnut. In the top section of this doughnut will be a service designation. This designation will either start with an “S” (service or spark ignition) for gasoline engines or a “C” (commercial or compression ignition) for diesel engines.

Last edited by Handy_Cruiser; 20 Feb 2021 at 02:53 pm.
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Old 08 Mar 2021, 03:28 am
Cool Cruiser
Join Date: Feb 2016
Location: Clearwater FL
Posts: 251
Default Re: diesel engine oil in a gas engine?

Here my one cent....

I use rosella t6 in a lot of gasoline engines. I use mobile one in my pt cruiser. I don't even keep track of oil changes. I just do it when I do it.

The pt cruisers got so many problems that one of 20 things would total the car more often then what type of oil you use.

I like to use good(more expensive) oil in my stuff. Im really not sure if it works better or not.

I do know from experience, in jet ski rental skis. Yamaha vx.... we run rotella t6 and the skis go past 1000 hours. In that time we rebuilt the jet pump 4 times, the mineshaft goes out at around 600.

But when you get to about 1300 hours there are all these other issues. steering cables, electronic reverse problems, metal parts rusting and corroding.

Actually the engines just run and run. however I know of other company who uses conventional oil. There skis run up past 1000 hours too just fine.

There skis are run down more because the owners choice too use the cheaper oil is also reflected in his other maintenance habits.

I would like to try the oil analysis stuff for fun some day.
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Old 08 Mar 2021, 07:10 pm
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Join Date: May 2014
Location: Central Florida
Posts: 4,454
Default Re: diesel engine oil in a gas engine?

Funny...CNET just released a video today on this very subject.
They said don't use Diesel Oil in a Gas Engine because you will most likely ruin the Catalytic Converter.
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