Can I Use Diesel Oil in My Gas Engine?

It’s good to familiarize yourself with the topic as there are particular conditions which you may benefit from using diesel oil or perhaps you have a fleet and are looking for one oil for everything, one size fits all.. The short answer: It depends on the brand – the approach to the end user.. Read on.

John Baker|Jul 19, 2019 8:12 AM

The simple answer: Yes, you can use diesel oil in a gas engine, provided the diesel oil meets the appropriate specifications and viscosity requirements of your engine.

For example, if your gas engine calls for a motor oil that meets the API SN specification, you can safely use a diesel oil of the correct viscosity that meets the API SN spec. For the typical gasoline application, a diesel oil isn’t required and the more appropriate choice is a quality gasoline motor oil for both performance and value.

The detailed answer: It’s common for some owners of modified gasoline-powered vehicles to favor diesel oils over their gasoline counterparts.

Many assume diesel oils are more durable and more capable of withstanding the increased heat of a powerful, turbocharged engine.

Others lean toward higher-viscosity oils to protect against wear, and it’s sometimes easier to find a 40- or 50-weight diesel oil than a gasoline motor oil. Others favor the increased detergency of diesel oils.

While you can use diesel oil in a gas engine, provided it meets the appropriate specifications and viscosity requirements, there’s far more to the topic than that, as I learned after talking to Mark Nyholm, AMSOIL Technical Product Manager – Heavy Duty.

AMSOIL Sioux Falls Dealer note: Call me if you have any questions on these items. I can help you dial in on the best oil for your particular need. 605-274-2580

Can diesel oil safely be used in gas engines?

Nyholm: It depends on the specifications the diesel oil carries and the recommendation of the original equipment manufacturer (OEM).

The American Petroleum Institute (API) publishes its “C” category of specification for diesel oil (currently CK-4) and its “S” category for gasoline motor oil (currently SN). It’s common for today’s diesel engine oils to carry both the API CK-4 and SN specifications.

Though they’re truly designed for diesel applications, they can be used in gasoline applications for those drivers who want to use one oil in all applications. If the diesel oil carries both specs, feel assured the oil is safe to use in diesel and gas applications. If the diesel oil does not carry the “S” category, I strongly recommend against using it in gasoline applications.

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Why do some motorists favor diesel oil over gasoline motor oils?

Nyholm: There are many reasons people choose the oil they use.

Since oil is not top-of-mind with many motorists, it’s typical for people to purchase based on viscosity alone. Many gasoline engines today call for 5W-30, with more and more requiring 5W-20, meaning those viscosities are typically what’s readily available. So, if you’re looking for a 5W-40 or 15W-40, it’s often easiest to find that viscosity in the diesel engine oil aisle.

Others use diesel oil under the assumption it’s a more “heavy-duty” product and must be better than gasoline motor oils.

They may have been told diesel oil is formulated with special components not available in gasoline motor oils, such as more robust detergency additives to handle the soot inherent to diesel engines. In their minds, diesel oils are analogous to better protection.

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Do most gasoline engines really need some of the additives in most diesel oils?

Nyholm: Diesel and gasoline oils are formulated with a variety of additives that improve wear protection, corrosion protection, resistance to foaming, viscosity retention and more. Whether the application is gasoline-powered or diesel-powered, many of the same additives are used based on what we are asking them to do in the formulation.

Now, there are additives designed to manage the byproducts of combustion, and some of those byproducts change, depending on whether you’re burning gasoline or diesel. If you’re running a gasoline engine, it’s best to use an oil that contains the correct additives to handle the byproducts of gasoline combustion. The same holds if you’re operating a diesel engine.

When should someone use diesel oil in their gas engine?

Nyholm: If your gasoline engine is heavily modified to put out more horsepower, using a diesel oil can be beneficial. It’s likely modified engines will need a higher viscosity to withstand the increased stress. You can turn to diesel engine oils for those needs or you might want to consider a racing oil, depending on your engine modifications and lubrication requirements.

Many times the engine builder will help provide insight as to what success they have found. Outside of that, if you have a bone-stock gasoline-powered application it’s best to stick with a gasoline motor oil.

They are designed for that type of application and have the components required to manage that engine. Sure, you can run a diesel oil in a gasoline engine; however it’s likely the formula has additional components your gasoline application doesn’t require, which might end up costing you more money.

AMSOIL formulates a complete line of gasoline and diesel oils for nearly anything you have. They’re dialed in to deliver outstanding protection for their intended applications. Consult the AMSOIL product guides for recommendations for your vehicle.

Find AMSOIL Products for Your Vehicle

Synthetic Warehouse Note: Mark forgot to mention in this last section a popular need for diesel in gas engines are customers who want one oil for their business or fleet. AMSOIL has products marketed for one size fits all. One popular is our first product which is excellent for RV’s motorcycles and fleets – It’s a 10W-40 that flows nicely and great for anything pre 1999. Check out the AMO 10W-40.

Another is a 5W-30 which makes a lot of sense and is in the newer Signature Series Diesel line – the DHD 5W-30 which is great for the latest API specifications, classics, Ford diesels, cars, mowers and equipment. Excellent for golf courses.

Automatic Transmission Fluid & Manual Transmission Fluid: What’s the Difference?

John Baker|Apr 09, 2019 11:06 AM

Back in 2006, original equipment manufacturers (OEMs) offered buyers the choice between an automatic and a manual transmission in 47 percent of new cars. Fast forward to 2018, when only 2 percent of vehicles sold had a manual transmission, according to edmunds.com.

Even with manual transmissions on the endangered species list, questions about automatic vs. manual transmission fluid still arise. Whether you opt for a stick or a slush box, you want to use the correct transmission fluid to maximize its performance and life.

Four responsibilities of a good automatic transmission fluid

The differences between automatic and manual transmission fluid lie in what each fluid must do. You don’t have to be an engineer to know that an automatic transmission is far more complex than a manual. Fittingly, so is the fluid it requires to function properly.

Automatic transmission fluid must perform several functions, including…

1. Act as a hydraulic fluid

Automatic transmissions use pressurized fluid to change gears. In essence, automatic transmission fluid is hydraulic fluid.

When your vehicle’s computer decides its time to shift gears, it sends an electric signal to the appropriate transmission solenoid. The solenoid directs fluid through a complex series of passages in the valve body to engage the correct gear. The fluid squeezes a series of plates together inside a clutch pack to connect the engine to the transmission output shaft and route power to the wheels.

In a properly functioning transmission, this all happens instantly and goes largely unnoticed.

However, fluid that’s too thick (it’s viscosity is too high) can fail to flow quickly for crisp, confident shifts. That’s one reason automatic transmission fluid has a lower viscosity than manual transmission fluid.

Fluid that has accumulated foam can also fail in its role as a hydraulic fluid. The foam bubbles collapse under pressure, causing elongated or inconsistent shifts (not to mention gear wear). For that reason, automatic transmission fluid must contain foam inhibitors.

2. Deliver the correct frictional requirements

As noted, pressurized automatic transmission fluid squeezes the clutch packs together to engage the correct gears. These clutch packs are comprised of bare metal plates and plates coated in friction material. Engagement and disengagement must occur seamlessly to provide the driver with the best driving experience.

The fluid’s frictional properties determine whether this complicated choreography of moving metal and fluid creates crisp shifts or has you scheduling a time to change transmission fluid.

As such, automatic transmission fluid is formulated to provide precise frictional properties not required of manual transmission fluid.

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3. Protect gears from wear

Automatic transmissions contain an array of sun, planet and ring gears that require lubrication to protect against wear. The fluid must form a durable fluid film on metal surfaces to prevent metal-to-metal contact and wear.

4. Fight heat

Heat is automatic transmission fluid’s number-one enemy. It chemically breaks down the fluid (known as oxidation). Fluid that has broken down leads to sludge and varnish, which can clog narrow oil passages and contribute to clutch glazing. Soon, your vehicle can begin to shift hard, jerk or hesitate.

Automatic transmissions typically run hotter than manuals, meaning the fluid must provide enhanced protection against heat. That’s one reason some vehicles have automatic transmission fluid coolers.

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Three responsibilities of a good manual transmission fluid

Just because they’re less complex doesn’t mean manual transmission lubrication requirements are simple. A good manual transmission fluid must serve several roles, including…

1. Enable smooth shifts

Nothing connects vehicle and driver like a smooth-shifting manual gearbox. Enthusiasts won’t tolerate a transmission fluid that interferes with that link.

Here, we have some cross-over between automatic and manual transmission fluid. But they go about enabling smooth shifts differently based on different component architecture.

Most manual transmissions are equipped with synchronizers. As the name suggests, the synchro equalizes its speed with that of the gear being engaged, allowing a smooth shift. Without it, the gears spinning at different speeds would clash as they try to mate.

The synchronizer unit is comprised of two main components: the sleeve and the blocker or synchronizer ring. When the driver selects, for example, first gear, the sleeve moves to the first gear and locks onto the gear engagement teeth, also known as dogs. Depressing the clutch pedal and selecting second gear results in the sleeve moving the other way and selecting second gear in the same fashion.

Before the sleeve can lock onto the gear, the rotational speed of each must first be synchronized. The friction between the blocker ring and a cone on the face of the gear equalizes their speed, allowing gears to mate without clashing. The entire process happens quickly and goes unnoticed in correctly operating transmissions.

Lubricant viscosity plays a vital role in shift feel.

Viscosity that is too high could prevent shifting until the transmission warms up or result in abnormally high temperatures during operation. Viscosity that is too low could cause the synchronizer and dog gear to engage too quickly, resulting in grinding or hard shifts and abnormal transmission wear.

2. Fight wear

Again, manual transmission fluid must protect against wear, just like an automatic transmission fluid. Manual transmission fluid, as noted earlier, tends to be a higher viscosity than automatic transmission fluid. This helps the fluid develop a thick, durable protective film.

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3. Protect brass synchronizers

Synchros are usually made of brass, which is softer than other metals. Certain lubricant additives aren’t compatible with brass and can damage the synchros.

The properly formulated manual transmission fluid for your vehicle will protect synchros to ensure they last as designed and promote smooth shifts.

As you may have figured out, automatic transmission fluid can, in some cases, work fine in manual transmissions. Which raises another question…

Will automatic transmission fluid work in a manual transmission?

Yes – provided the original equipment manufacturer recommends it. It’s important to check your owner’s manual to make sure before dumping ATF in your manual transmission.

In fact, some manuals may call for a gear lube or even a motor oil in older units.

I should also point out that continuously variable transmissions (CVT), popping up on more vehicles today due their increased efficiency, take their own fluid. And so do dual-clutch transmissions (DCT), which you’ll find on many sports cars.

Whichever you prefer, AMSOIL formulates a transmission fluid to help maximize transmission performance and life.

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Category: Knowledge Base

Do’s and Dont’s using Diesel Oil in Gas Engines