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Should I Switch to a Lighter Viscosity Oil in Winter?

Generally with todays vehicles it’s not an issue but you should check the particular recommendations in the owners manual

Motorists sometimes ask if they should use a lighter viscosity of motor oil once winter arrives.

Yes – provided your vehicle manufacturer allows it. 

Run out to your vehicle and fish the owner’s manual from the glove box. Or open a digital copy on your phone.

Somewhere in the back you should find the motor oil recommendations. Many vehicles, particularly domestic, call for a lone viscosity of motor oil. It’s likely 5W-20 or 5W-30. That’s what you’re supposed to use all the time. Doesn’t matter if it’s -20ºF (-29ºC) or 100ºF (38ºC) outside. The engine was designed and manufactured to operate most efficiently using that particular viscosity of motor oil.

But some vehicle manufacturers – often foreign – recommend different motor oil viscosities depending on ambient temperature. You may find a chart in the owner’s manual like the one below that shows which viscosity you can use depending on the temperature. The manufacturer typically recommends a lighter viscosity when the temperature drops during the winter.

Typical viscosity temperature use chart in car's owners manual

Your vehicle owner’s manual may contain a viscosity chart like this one.

In this case, we recommend using the lightest recommended viscosity during the winter.

Why?

Two reasons:

  • Maximum wear protection at startup
  • Easier cold starts

To understand, you have to understand motor oil viscosity. If you’ve navigated to this page after a Google search, you probably know something about viscosity already. But a little refresher can’t hurt. (Check out this post for a detailed explanation of viscosity.)

Viscosity refers to the oil’s resistance to flow and is its most important property. The lower the oil’s viscosity, the more readily it flows at cold winter temperatures. Of course, the opposite is true – the higher the oil’s viscosity, the more slowly it flows when cold. That means an 0W-20 oil will flow better when it’s cold than a 10W-30.

Dub-ya

Which brings me to my next important point.

The oil’s “W” viscosity describes its characteristics when it’s cold. And by “cold” we mean 40ºC (104ºF). The second number (e.g. the “30” in “5W-30”) describes the oil’s characteristics once your engine reaches normal operating temperature, or 100ºC (212ºF).

Engineers agree that most engine wear occurs at startup. One reason is because gravity pulls much of the oil into the sump as the vehicle sits overnight.

When you start the vehicle the next morning – even if it’s not that cold outside – a few critical moments pass before the motor oil travels through the oil pump and navigates the narrow oil passages to reach components throughout the engine. It’s during those moments that accelerated wear can take place.

As such, it’s beneficial to use an oil that flows readily at startup to reach engine components as quickly as possible.

Since lower-viscosity oils flow more readily, they provide better cold-weather startup protection compared to higher-viscosity oils.

On a side topic with AMSOIL if your vehicle calls for 5W-20 or 0W-20 both can be seen as interchangeable with the superior synthetic base oils used. Neither one make a cotton picken bit of difference unless we are at -45 all week, then the 0W-20 may be a little better.

From South Dakota to Texas many of our

Crank it up

Lower-viscosity oils also provide less crankshaft resistance as the engine turns over. When the temperature plummets below zero, the motor oil can thicken so much that it prevents the crankshaft from spinning fast enough to start the engine. This is particularly a problem with conventional oils since they contain waxes that thicken in the cold. Synthetic motor oil, in contrast, doesn’t contain waxes and, therefore, provides easier cold starts.

Check out the video to see for yourself.

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Along the same lines, oil that provides less resistance to moving engine parts also maximizes fuel economy. That’s the primary reason automakers are trending toward lighter viscosity oils in their new vehicles.

A word of caution…

It’s important to note that using a higher-viscosity oil does have its benefits, too. Higher viscosity oils tend to provide improved wear protection since they promote formation of a thicker fluid film on engine parts. They’re also more resilient to oil consumption than lighter viscosities.

Bottom Line: Switch to the lightest viscosity oil your vehicle manufacturer recommends in the winter. Doing so maximizes wear protection at startup while improving cold-weather starts.

FIND AMSOIL PRODUCTS FOR YOUR VEHICLE

The Difference Between GL-4 and GL-5 Gear Oil

The Difference Between GL-4 Manual Transmission and GL-5 Differential Gear Oil

The main difference between GL-4 and GL-5 gear oils is in the level of extreme-pressure (EP) additives.

It’s really very simple. They are not intended to be interchangeable and GL5 didn’t replace GL4.

by Eddie Yorkman, | July 5, 2022

If you’ve ever purchased gear oil, or spent any time looking at gear-oil specifications, you have undoubtedly come across the API GL-4 and GL-5 specifications. You may have wondered, what is the difference between GL-4 and GL-5 gear oil? Where can I buy GL-4 and GL-5 gear oil?

Well that’s if you were even able to find any in the modern auto parts stores.

Severity – Hypoid gears vs Helical

The American Petroleum Institute (API) classifies gears using GL ratings, ranging from GL-1 to GL-5. Higher GL rating numbers represent more severe applications; GL-1 is the least severe and can usually be satisfied with a motor oil, while GL-5 is the most severe GL rating.

EP additives

The main difference between GL-4 and GL-5 gear oils is in the level of extreme-pressure (EP) additives. EP additives effectively protect gears by providing a sacrificial layer on gear surfaces; these additives are essential for protecting gears operating under heavy loads and extreme temperatures. A typical GL-5 gear oil provides about twice as much EP additive in its formulation compared to a GL-4 gear oil.

Where are GL-4 and GL-5 gear oils used?

GL-4 gear oils are typically recommended for spur and helical gears found in manual transmissions and transaxles operating under moderate speeds and loads.

GL-5 gear oils are typically recommended for hypoid gears in automotive axles operating under high-speed, high-load conditions.

What type/weight gear oil should I use?

For top protection and performance, it is best to consult your owner’s manual/Shop manual for the manufacturer’s recommendation. There, you will find both the specified viscosity (75W-90, 75W-140, etc.) and specification (API GL-4, API GL-5, API MT-1, etc.) recommended for your application. Almost all hypoid gear sets require GL-5 due to the need for significant extreme-pressure protection.

Note the 2nd number is the KEY weight under operating temperatures and conditions. 990, 110, 140, 250, etc..  For example our 75W-80 covers and overlaps the recommendations where 80W-90, 85W-90 are written.

What’s the best gear oil for my vehicle?

AMSOIL SEVERE GEAR® Synthetic Gear Lube excels in protecting gears and bearings from the rigors of severe-service operation. By design, it resists breakdown from high heat, preventing acids and maintaining a barrier to prevent metal-to-metal contact while conditioning seals. Its wax-free construction also improves cold-flow properties, improving fuel economy and cold-weather performance.

Now 75W-85 is available January 2025

• Superior film strength
• Controls thermal runaway
• Protects against rust and corrosion
• Helps reduce operating temperatures
• Maximum efficiency
• Long oil, seal and equipment life
• Flexible easy-pack for clean, fast installation

SEVERE GEAR is recommended in differentials, manual transmissions and other gear applications requiring an API GL-5 gear oil. It can also be used in axles where an API GL-4 lubricant is recommended.

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