AMSOIL Signature Series Max-Duty 5W-40 Synthetic Diesel OilA reader asks: I’ve got a 2018 GMC Sierra 2500 with the L5P Duramax diesel engine. I see that 15W-40 oil is suggested for this engine. Can I use 5W-40 in the winter?

Our answer: Yes, you can certainly use 5W-40 in winter (and summer) in your Duramax. While 15W-40 is suggested as the predominant viscosity for your engine, GM does recommend 5W-40 for temps below -18°C (0°F). AMSOIL’s official stance is that their 5W-40 synthetic diesel oils are safe and perfectly suited for year-round use under all conditions and loads. Naturally, 5W-40 is highly recommended for winter use, but there is absolutely no downside to using it in summer as well.

We offer two synthetic 5W-40 diesel motor oil options. The ultra-premium AMSOIL Signature Series Max-Duty 5W-40 and the value-priced AMSOIL Heavy-Duty Synthetic 5W-40.

Is There Any Advantage To Using 15W-40 Over 5W-40?

No. Remember that both 5W-40 and 15W-40 have a 40-weight viscosity. Note that both are offering roughly the same viscosity protection at operating temperature.

The main advantage that 5W-40 offers is faster oil flow during cold-starts.

It is true that 15W-40 has been the predominant diesel oil viscosity for decades. The reason that 15W-40 was a mainstay was its relatively slim spread between the winter weight (15W) and the operating temperature weight (“40”). With previous generations of motor oil technology, a wider spread between winter weight and operating weight (such as 5W-40) was more prone to shearing and thinning.

AMSOIL Heavy-Duty Synthetic 5W-40 Diesel Oil.Today’s motor oils (especially synthetic oils) have a much more linear viscosity across the temperature spectrum. As a result, they are much less prone to being too thick in the extreme cold or thinning out in extreme heat. Therefore, a good 5W-40 will provide flawless protection all year-round.

That is why a 5W-40 can now safely replace 15W-40 for year-round use.

What Is The Difference Between AMSOIL Signature Series Max-Duty and Heavy-Duty Diesel Oils?

Signature Series Max-Duty is AMSOIL’s most sophisticated formula. It delivers their absolute best wear control.

In the Detroit Diesel DD13 Engine Scuffing Test, Signature Series beat the minimum standard by 600%. Heavy-Duty Series beat the standard by 400%.

Signature Series Max-Duty is overbuilt for extended oil change interval capability. Heavy-Duty Series should be changed at the interval suggested by the manufacturer or by the oil life monitor.

Heavy Duty Series has a lower price tag. It was brought to market for commercial fleets, the installer market and value-minded consumers.

We can sell AMSOIL Signature Series Max-Duty and Heavy-Duty Series 5W-40 in Canada and the United States. Contact us using the form on this page for a wholesale price list.

AMSOIL Metric 15W-50 Synthetic Motorcycle OilA reader asks: I’ve got a Ducati Monster 1200. AMSOIL Metric 15W-50 Synthetic Motorcycle Oil is suggested for this model. This engine revs up to over 9000 rpm, so it needs oil with good wear protection and foaming resistance. What is the zinc and phosphorus content of this oil? I can’t find this information anywhere.

Our answer: The fixation on zinc and phosphorus content in motorcycle oil is old thinking. With today’s ashless additive technology, zinc and phosphorus levels are far less relevant for some motor oils. Let us explain.

AMSOIL Metric 15W-50 carries the JASO MA2 and API SM specifications. The JASO MA2 oil standard signifies that a motorcycle oil is safe for catalytic converters. High levels of traditional motor oil additives like zinc and phosphorus can damage catalytic converters. Therefore, alternate technology has to be employed in order for the oil to provide adequate wear protection.

Metric 15W-50 Synthetic Motorcycle Oil employs the latest “ashless” additive technology. Therefore, it has less zinc and phosphorus than some of AMSOIL’s more traditional motorcycle oil formulas.

Why Zinc And Phosphorus Numbers Are Not Important Anymore

Let’s compare the zinc and phosphorus content of AMSOIL V-Twin Synthetic 20W-50 and AMSOIL Metric Synthetic 15W-50. The V-Twin 20W-50 has a more traditional formulation than Metric 15W-50.

  • AMSOIL Metric 15W-50- Zinc- 841 ppm, Phosphorus- 767 ppm
  • AMSOIL V-Twin 20W-50- Zinc- 1300 ppm, Phosphorus- 1100 ppm

Based on these numbers, is the V-Twin 20W-50 vastly superior to Metric 15W-50? Not at all! AMSOIL Technical Services tells us that the wear control between the two products is identical. They also tell us that ashless additives bring other advantages.

For instance, when there is blow-by, old-style heavy-metal additives (such as zinc and phosphorus) from can create engine deposits. Ashless additives do not create these deposits.


Ashless motor oil additive technology has revolutionized motor oils in the passenger car and heavy-duty diesel engine oil segments. This technology is also a major player in part of the motorcycle oil market. Simply looking for the motorcycle oil with the highest zinc and phosphorus numbers won’t automatically point to the best product.

AMSOIL Ea Motorcycle Oil FiltersA reader asks: I’ve been researching oil filters for my Harley-Davidson motorcycle. Harley-Davidson has oil filters that will stop particles down to 5 microns, while AMSOIL motorcycle filters only stop particles down to 20 microns. I thought that AMSOIL oil filters were supposed to be one of the better filters out there? Why are Harley filters so much better?

Our answer: The oil filter micron ratings provided by both AMSOIL and Harley-Davidson “Super Premium5” oil filters is like comparing apples to oranges. Each company is measuring their micron ratings on completely different scales. Therefore, the micron numbers are not at all comparable.

AMSOIL offers their motorcycle oil filter ratings on an “absolute” scale. Based on this measurement, their motorcycle oil filters are 98.7% efficient at stopping particles that are 20 microns in size or larger. This is a considered to be a very strong efficiency rating.

For reference, a decent automotive oil filter would stop 98.7% of particles 30 microns or larger.

Harley-Davidson provides their micron numbers on an “nominal” scale. Their nominal claim of “5-microns” with their “Super Premium5” oil filter is not telling the whole story. Filters makers claiming ultra-low nominal micron ratings aren’t mentioning the “efficiency”.

Let’s be clear. Harley-Davidson Oil Filters are definitely not removing 100% of particles down to 5-microns. This would make the oil filter so restrictive that it would go into by-pass mode every single time you rolled onto the throttle. Under most all riding conditions, that would be like having no oil filter.

What is the Difference Between “Nominal” And “Absolute” Oil Filter Ratings?

Absolute filter ratings are determined under controlled testing. The absolute filter rating is shown as 98.7% of particles of a stated diameter being stopped by the oil filter. In the case of AMSOIL Motorcycle Oil Filters, they stop 98.7% of particles measuring 20 microns in size or larger.

Nominal ratings such as the 5-micron rating touted by Harley-Davidson has zero meaning without mentioning efficiency. Chances are high that the H-D filters are about 50% efficient at 5 microns. Where a Harley 5-micron oil filter would score in an absolute filter micron test is anyone’s guess.

What Is a Micron?

A micron is a unit of measurement that is 0.001 millimeters or 0.000039 inches. For example, bacteria are 2 to 3 microns in diameter and a red blood cell is 5 microns. The diameter of human hair averages 70 to 80 microns.

Bottom Line

To sum up, Harley oil filters might be well-built and near the top of the heap. But it’s very hard to tell. The nominal 5-micron rating touted by Harley-Davidson has no meaning without mentioning efficiency.

AMSOIL Signature Series Max-Duty Synthetic 5W-30 Diesel OilA reader asks: I’ve got a 2019 Ford Transit Connect van with the 1.5L EcoBlue diesel engine. It requires a motor oil meeting the Ford WSS-M2C214-B1 specification. The engine oil offered by Ford is Motorcraft SAE 5W-30 F-150 Diesel Motor Oil. Do you offer a motor oil that is correct for this engine?

Our answer: Yes, we have a motor oil for the Ford Transit Connect van with the 1.5L EcoBlue motor. AMSOIL Signature Series Max-Duty Synthetic 5W-30 Diesel Oil meets the Ford WSS-M2C214-B1 spec. It is a 100% synthetic substitute for Motorcraft SAE 5W-30 F-150 Diesel Motor Oil.

Benefits Of AMSOIL Signature Series Max-Duty 5W-30

  • Industry-leading wear protection
  • Delivers consistent performance in extreme heat or arctic cold
  • Resists engine deposits
  • Capable of long service intervals
  • Combats oil consumption

The bottom line is that AMSOIL Signature Series Max-Duty Synthetic 5W-30 is highly capable of providing steadfast wear protection in large displacement, mega-horsepower diesel engines. Therefore, it will withstand everything the EcoBlue engine can throw at it.

Where To Buy AMSOIL Signature Series Max-Duty 5W-30 Diesel Oil

We can sell this synthetic 5W-30 for Ford Transit Connect 1.5L EcoBlue engines at the best prices with our wholesale options. We ship from 11 warehouses in the United States and 2 locations in Canada.

Contact us for a price list using the form on this page or call us at 1-800-748-5781.

AMSOIL Synthetic 2-Stroke Injector OilA reader asks: I’m looking for oil for my 2003 Sea-Doo GTI 787 with a 2-stroke engine. The previous owner used the BRP XPS 2-Stroke Mineral Oil. I’m afraid to change to a different oil as I do not want to hurt the engine. What do you suggest?

Our answer: Switching to a full synthetic two-stroke oil from a mineral-based oil will not cause any damage or performance issues. In fact, a good full-synthetic 2-stroke oil will dramatically improve wear control and enhance performance. There is zero downside to switching over to synthetic oil and plenty of upside.

Here are some of the benefits that you will notice by switching from a conventional (or “mineral”) 2-stroke oil to synthetic.

  • Less exhaust smoke
  • Lower friction and crisper throttle response
  • Reduced engine and power valve deposits
  • Improved wear control
  • Greater resistance to extreme heat

The full-synthetic upgrade we offer is AMSOIL Synthetic Injector Oil. It will deliver cleaner operation, less smoke, lower friction, better wear control and improved performance over the XPS Mineral 2-Stroke Oil. All of these features are available at a very competitive price versus BRP XPS Mineral Oil from your Sea-Doo dealer.

AMSOIL Synthetic Injector Oil is smart substitute for BRP XPS Mineral Oil at a very reasonable price. Request a wholesale price list using the form on this page.

AMSOIL Arctic Synthetic GreaseA reader asks: Do you carry an equivalent of Mobil Epic EP 102 Grease? This will be used in medium-duty worm drives in both extreme winter cold and summer.

Our answer: We believe that we have an upgrade over the semi-synthetic Mobil Epic EP 102 product.

A unique aspect of Mobil Epic EP 102 is that it has a relatively rare NLGI grade of “1.5”.

NLGI # 1 grease would traditionally be considered a winter grease, while NLGI # 2 grease is considered a summer grease. The vast majority of grease sold is NLGI #2. For most of the northern half of North America, an NLGI # 1 grease can be used year-round in all but the heaviest applications.

While we don’t offer a semi-synthetic NLGI #1.5 grease, we think that a full-synthetic NLGI # 1 product would actually cover a wider temperature range.

Our replacement for the semi-synthetic Mobil Epic EP 102 Grease would be the 100% synthetic AMSOIL Arctic Synthetic Grease. Don’t let the “Arctic” title fool you. This full-synthetic, extreme pressure (EP) grease is very capable for summer use. Its synthetic formula allows for complete four-season use.

A Full Synthetic Substitute For Mobil Epic EP 102 Grease

AMSOIL Arctic Grease has an operating range of -59°C to 157°C (-75°F to 315°F). The Mobil Epic EP 102 product has an operating range of -50°C to 150°C (-58°F to 302°F). The AMSOIL Arctic Grease has a slightly wider operating range.

When it comes to extreme pressure performance, the AMSOIL Arctic Grease outperforms the Mobil Epic EP 102 product. The “4-Ball Weld Test” measures the load carrying ability of a given grease. In this test, a steel ball is rotated under pressure against three other steel balls. The amount of weight required to seize this steel ball against the other three gives us the 4-Ball Weld Test number.

AMSOIL Arctic Synthetic Grease withstands the 4-Ball Weld Test until 400 kg of pressure is applied. Mobil Epic EP 102 Grease stops out at just 250 kg.

In conclusion, AMSOIL Arctic Grease is much more than just a “winter grease”. It has a wider operating temperature range and a much greater ability to withstand extreme pressure over Mobil Epic EP 102 Grease.

We can offer AMSOIL Synthetic Arctic Grease at wholesale in Canada and the US. Contact us for a price list using the form on the page

AMSOIL Interceptor Synthetic 2-Stroke Injector OilAMSOIL Interceptor Synthetic 2-Stroke Oil now meets and exceeds the requirements for the JASO FD industry specification. Why does this matter? Ski-Doo recently started recommending the use of JASO FD-compliant 2-stroke oils for their E-TEC snowmobile engines.

AMSOIL Interceptor has been extensively tested for use in Ski-Doo E-TEC engines. The addition of this spec further cements Interceptor’s credentials as the ideal 2-stroke oil for E-TEC engines. We have received nothing but rave reviews about Interceptor from our E-TEC customers. Best of all, the 100% synthetic Interceptor is priced lower than Ski-Doo/BRP 2T E-TEC Synthetic Oil or BRP Synthetic 2-Stroke Oil.

What Is The “JASO FD” 2-Stroke Oil Specification?

JASO FD is a two-stroke oil industry specification set by the Japanese Automotive Standards Organization.

As with previous JASO two-stroke oil specs, JASO FD has a number of performance and smoke guidelines. This newest “FD” specification places a much greater emphasis on detergency and engine cleanliness.

How Is AMSOIL Interceptor Suitable For Ski-Doo E-TEC Engines?

The direct injection Ski-Doo E-TEC engine sets new standards in terms of fuel efficiency, low emissions and horsepower per cubic centimeter.

One of the main features of E-TEC engines is that they consume very little 2-stroke oil. A relatively small amount of oil is the difference between peak performance or an expensive engine failure. For this reason, E-TEC engines require a very advanced synthetic 2-stroke oil. AMSOIL Interceptor offers highly sophisticated synthetic anti-wear chemistry. Extensive testing in Ski-Doo E-TEC engines has proven that Interceptor provides outstanding wear control.

Another important oil requirement for E-TEC’s is cleanliness. The precise E-TEC engines require very clean internals. This is the main reason why BRP is requiring the use of 2-stroke oils that meet the JASO FD spec. Interceptor has world-class cleaning ingredients that keep E-TEC engines operating at their peak. It also keeps RAVE variable exhaust power valves clean which optimizes performance. AMSOIL Interceptor’s clean-burning performance exceeds the JASO FD requirements.

One of the special features of the E-TEC engine is a (mostly) one-pull start in extreme cold. AMSOIL Interceptor pours down to -56°C (-69°F) for instant cold-start oil flow.

Interceptor ticks all of the boxes for E-TEC use. It provides elite wear protection, high film strength, minimal friction, robust detergent ingredients and low-smoke.

In conclusion, Interceptor offers all of these features at a lower price than BRP 2T E-TEC Synthetic Oil.

Request wholesale pricing for AMSOIL Interceptor Synthetic 2-Stroke Oil using the contact form on this page.

A reader asks: I have a 2006 Honda S2000 that is driven just 1000 miles per year. The few miles that it does see are very easy miles. I last changed the rear differential gear oil about 4 years and 5000 miles ago. The car is stored in a warm garage and the diff has never been exposed to moisture. The gear oil used was AMSOIL Severe Gear 75W-90. How often should I change this gear oil when the car sees so few miles?

Our answer: Many car enthusiasts own have vehicles that they affectionately refer to as a “garage queen”. While these cars may see very few miles, maintenance still has to be a consideration.

When it comes to gear oil service intervals in sparsely driven cars, there isn’t much consensus. As differential oil that isn’t exposed to moisture, extreme heat or heavy loads has a very easy life.

That being said, everything oxidizes over time and eventually the additive package of the gear oil will undergo “fallout”. A very conservative service interval would be every 5 to 7 years. We are confident that a robust product like Severe Gear would last much longer. But this is likely a good window to freshen up the gear oil. This will keep corrosion at bay, wear control at its best and seals supple.

Other Stored Car Maintenance Notes

Regular maintenance is still required for cars that are rarely driven. Here are some notes on the subject.

  • Fuel degradation is a massive concern and should be considered at all times. Make sure to add gasoline stabilizer when filling the tank. Degraded fuel can foul carburetors or injectors and fuel lines. Bad gasoline can also cause depositing and significant engine performance issues.
  • Still on fuel issues, it’s a good idea to add carburetor or injector cleaner to the gas tank at least once per year.
  • Change the engine oil at least once per year. This is the case regardless of how few miles the car travels over a year. Combustion by-products allow for acid formation in the oil over time. Older vehicles also have a higher tendency toward fuel dilution in the oil. Changing the motor oil just before long-term storage is the best course of action.
  • Brake fluid tends to draw moisture out of the air, even though it is a sealed system. Brake fluid should be changed slightly more often than rear differential gear oil (every 4-5 years or so). Fresh brake fluid prevents the creation of rust and corrosion in the braking system.

AMSOIL Signature Series 15W-40 Max-Duty Synthetic Diesel OilA reader asks: I’ve got a 2003 Dodge Ram 2500 with the 5.9L Cummins engine. Should I use the older generation of CI-4+ diesel oils? Are the newer API CK-4 diesel oils good for this engine? My understanding is that these engines have flat tappet cams and I hear that the newer diesel oils do not have enough zinc to protect them.

Our answer: The short answer is that (for your older engine), virtually any of our diesel motor oils will be highly effective. The long answer may surprise you.

There is a common misconception that the newest diesel motor oils meeting the latest API CK-4 specification are somehow weaker or less robust than previous generations of diesel oils. This is patently false.

In fact, API CK-4 diesel oils are considerably more sophisticated and capable than diesel oils meeting previous specifications such API CI-4+. Older diesel oil formulas meeting API CI-4+ are weaker in terms of protective capabilities.

The introduction of the CK-4 spec was a tremendous challenge for motor oil makers. Diesel engines and their emissions components have become very sophisticated in recent years. The CK-4 requirements required oil makers to ramp up their game to meet much higher standards. Here are some of the upgrades of the API CK-4 spec over the previous CJ-4 spec.

  • Increase in high temperature capabilities
  • Improvement of piston and bore wear protection
  • Better deposit control
  • Resistance to degradation of hot and cold weather properties
  • Improved shear stability
  • Enhanced aeration resistance
  • Resistance to catalyst and particulate filter fouling
  • Improved oxidation resistance

What About AMSOIL Heavy Duty Series Vs. Older Diesel Oils?

AMSOIL Heavy Duty Diesel Series is a less expensive API CK-4 option to the flagship Signature Series Max-Duty Diesel Series. Heavy Duty Series was created as a budget-friendly option for fleets, the oil change installer market and those looking for a less expensive synthetic product.

We asked AMSOIL Technical Services how the API CK-4 AMSOIL Heavy Duty 15W-40 might compare to an older generation product like the API CI-4+ “AME” AMSOIL Heavy Duty Diesel and Marine 15W-40. Their answer was “It’s not even close”. While the Heavy-Duty Diesel And Marine 15W-40 is a very robust and competent product, development stopped when the API CI-4+ specification was replaced in 2007. The ball has been moved way down the field since then. So even the less expensive API CK-4 diesel oils are a step up over the previous generation.

Signature Series Max-Duty is considerably more advanced. It offers the most advanced synthetic base oil and additive technology available. As a result, Signature Series Max-Duty is an upgrade over Heavy-Duty Series in terms of wear control and service life.

What About Flat Tappet Cams?

Flat tappet cams are relatively common to many diesel engine types. The biggest concern with flat tappet cams is wear protection. Specifically, does the motor oil contain enough ZDDP (Zinc Dialkyl Dithio Phosphate) and phosphorus?

Flat tappets in diesel engines are less of a concern than having flat tappet cams in something like a gasoline-powered street rod motor. Street rods and drag racers run at much higher RPM and tend to have much heavier valve springs compared to stock diesel engines. Also, modern passenger car/gasoline motor oils have much lower zinc and phosphorous limits. These levels are insufficient for flat tappet wear protection. So owners of gasoline engines with flat tappet camshafts have to be very mindful of their motor oil choice.

This is not a concern with diesel engine oil. Diesel motor oils are designed for all diesel engine types. Contrary to popular belief, the newest API CK-4 spec has not limited zinc and phosphorous to dangerously low levels with 40-weight viscosities. This would include 0W-40, 5W-40 and 15W-40, etc.

The API CK-4 AMSOIL Signature Series Max-Duty 5W-40 and 15W-40 has zinc levels over 1300 and phosphorus levels above 1200 ppm. Similarly, the AMSOIL Heavy- Duty 5W-40 and 15W-40 has zinc over 1100 ppm and phosphorus over 1000 ppm.

To contrast, the older AMSOIL Heavy Duty Diesel and Marine 15W-40 (API CI-4+) has 1377 PPM ZDDP and 1267 ppm phosphorus. This doesn’t necessarily mean that it will protect flat tappet engines better than the API CK-4 oils. The zinc and phosphorus level comparisons are a moot point. The newer API CK-4 chemistry is miles ahead of the older API CI-4+ formula. The newer CK-4 options will provide considerably better wear protection.


To sum up, do not be concerned about using the latest API CK-4 diesel motor oils in older engines. They are very much backward compatible with older engine designs and are a giant step forward in terms of wear control.

AMSOIL HP Marine Synthetic 2-Stroke OilA readers asks: I’ve got a 2009 Yamaha 20MLHH 2-stroke, 20 horsepower outboard engine. Yamaha recommends a 100:1 mix ratio. I see that AMSOIL HP Marine has a recommended premix ratio of 50:1. I feel that this ratio is too rich for this engine. Is there any way I can get the 100:1 AMSOIL Saber Outboard Oil in Canada? 

Our answer: Your Yamaha outboard engine can easily use AMSOIL HP Marine at 100:1. It can replace the OEM Yamalube 2M TC-W3 2-stroke oil (with less exhaust smoke). It is true that Saber Outboard Premix Oil is no longer offered in Canada. However, HP Marine is certainly not a downgrade for your engine.

While HP Marine has a suggested mix ratio of 50:1 on the label, it is no stranger to ultra-lean mix ratios. HP Marine has been heavily tested in Evinrude E-TEC engines at the “lean-mix” setting. This is the equivalent of an approximate 100:1 ratio. AMSOIL’s extensive testing under extreme loads at this lean-mix setting proves that it delivers outstanding wear protection.

Yamalube 2M TC-W3 2-stroke oil is only a partial-synthetic product. HP Marine is a 100% synthetic formula that offers the very latest two-stroke marine oil technology. Therefore, we would rate it as a considerable step up over the Yamalube product.

Features Of AMSOIL HP Marine

  • Low-smoke and odor
  • Robust synthetic wear protection
  • Resists carbon build-up
  • Provides excellent throttle response
  • Low aquatic toxicity
  • Protects against internal anti-rust and corrosion
  • For premix or oil-injected marine two-cycle engines

For US customers that have access to Saber Outboard, it is also an excellent choice for Yamaha outboards requiring a 100:1 premix ratio.

If you have questions or would like to request prices, contact us using the form on this page or call us at 1-800-748-5781.