Can you use diesel oil in gas engine? Diesel oil typically contains better additives than gas engine oil regardless of having similar viscosity. Diesel oil uses additives like zinc, ZDDP, and phosphorous, which provide better lubrication, especially for older camshaft motors.
Though you can use diesel oil in a gasoline engine, there are consequences. For instance, if you run diesel oil in a gas engine with a catalytic converter, you’d have to replace the cat converter sooner than expected.
Of course, lots of drivers use diesel oil for gasoline engines, but you’d mostly find it being used on older vehicles. You do not want to use it on a modern vehicle, especially regularly. If you add diesel oil to your gasoline motor oil by mistake, you may continue with it if the grades match.
What’s the Major Difference Between Diesel Oil and Gas Engine Oil?
The difference between diesel oil and engine oil is no big deal, though. Diesel formulation has less friction modifiers, making it less slippery. As mentioned earlier, it contains ZDDP (anti-wear) and more detergent than gas engine oil. It’s no problem if you have diesel engine oil in your gasoline engine by mistake. However, regular use in a vehicle with the catalytic converter can break the cat converter. The vehicle can’t pass exhaust tests, and you’d get poor fuel efficiency. In a vintage car using flat tappet valve trains, diesel engine oil enhances ZDDP sliding.
Can You Use Diesel Oil in Gas Engine?
Of course, you can use diesel oil in a gas engine as lubrication but is not recommended. Besides, automakers recommend the oil you should use. Diesel oil uses a formula quite different from gasoline oil, which is somehow incompatible with a gas engine.
The issue lies with the control properties in diesel oil, which are usually heavier than what we have in gas engine oil. For example, a typical older diesel vehicle uses 15w-40 oil, whereas some modern gas vehicles use 5w-20 motor oil.
Obviously, there is no match, meaning that by applying diesel oil in your car engine, you might be using heavier weight oil instead of a lighter weight. You can expect it to damage the engine, starting with a strange noise. And if a cat converter sits in the car, budget a potential replacement.
Also, some oils are designed for diesel and gasoline engines. This type of oil would be a multi-grade oil, and your manufacturer may still not recommend it. Most of the time, when manufacturers produce multi-grade oil, they first recommend it for use on a particular engine (oil or diesel) before mentioning that it can also be used for the other engine.
An example is SAE 15W40 CH4 oil, which is first recommended for a diesel engine, but is also applicable in a gas or petrol engine. Nevertheless, make sure to follow your vehicle manufacturer’s recommendation. Of course, they recommend specific grade oil for protective reasons.
You can use diesel oil in a car without a catalytic converter
If you have no catalytic converter in the car, you may use diesel engine oil and forget about cat converter replacement. Theoretically, diesel oil may function well with a gas engine, but the phosphorous content is excessive for the cat converter.
Most vehicle owners use diesel engine oil in vintage vehicles because these older vehicles require additional phosphorous to aid the flat tappet valvetrain.
Another reason why you can use diesel engine oil in a gas car without a cat converter is because of the additional detergent content. Extra detergents in diesel oil can remove unwanted deposits from the low-quality gas engine oils you used over time.
Gas engine oil does not contain as much detergent compared to diesel engine oil. The clean-up from gas oil is slower, but it’s okay since it is so designed for your car.
If you have a modern car without a catalytic converter, API SN oils are recommended; they are designed to enhance the roller-cam valve trains, and they also contain additives for improved fuel efficiency. If your vehicle is a higher revolution/temperature engine, they’d suit just right.
It is quite uncommon to find diesel engine oil in gas engine car viscosity requirement (0W-20 to 10W-30 viscosities).
Is it bad to put engine oil in a gas engine?
It is not so bad to put engine oil in a gas engine so far it uses the API grade (like SN) and viscosity recommended in the owner’s manual. For instance, if a diesel oil is API FA-4/SN, it is safe to use in a car that API SN oil is recommended. If the diesel oil is marked API FA-4, it may be bad for your gas car, and you must not add it to avoid damage or engine degradation.
Does diesel engine oil hurt gas engine?
Diesel engine oil will not hurt the gas engine unless the viscosity does not match your gas car requirement. Moreover, many car owners use diesel engine oil on their gas vehicles either mistakenly or consciously. When purchasing engine oil, the manufacturer mentions on the oil fill cap that you may refer to your owners/service manual if you’re unsure.
As mentioned earlier, diesel oil contains more detergents than gas engine oil. Instead of harming your vehicle engine in this aspect, it will help to clean the internal dirt, grease and deposits gathered in your car from recent poor oils.
A lower budget motor oil like Rotella T may be used in both diesel and gas engines. It not a recommended motor oil, but serves the purpose.
In essence, diesel oil may function as dual-purpose motor oil because you may use them in gasoline cars, too.
Final Thoughts
Note that not all diesel oils you find are compatible with gasoline engines. The setback is in diesel motor oil additives, which gasoline oil does not contain and that can damage your catalytic converter.
As mentioned earlier, some diesel oil manufacturers will include in the label that you may use it on gasoline cars that require a specific motor oil grade.
Older gas vehicles, especially V8 engines, with flat tappet cams perform considerably with diesel oils since it uses zinc to enhance the camshaft.
Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.
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