Do I Need to Change Motor Oil for Summer?


There is a long-lasting belief among some car owners in places with four seasons that you may need to change the oil in your car as temperatures climb or fall.

Motor oil is the lifeblood of your car. It needs to be able to flow freely over all the moving parts of your engine. Traditionally, the temperature of the oil changed how easily it flowed through the engine. Called viscosity, this is the physical measurement for how “thick” a liquid is. Motor oil in low temperatures could turn into something more like molasses, which could prevent it from properly coating the engine in a cold start.

However, if you use the right motor oil, it keeps a higher viscosity at a lower temperature. But, as the heat rises, the oil becomes too thin. Motor oil uses the term weight to describe its viscosity, which is where the numbers you have seen on all oil containers comes from.

There is good news, however. Motor oil has come a long way. You no longer really need to change your motor oil every season, because it changes for you. Known as multi-viscosity motor oil, it does exactly what the name suggests. As temperatures fall, the weight of the oil changes to allow it to flow easily over the engine. Then, once summer comes back around, the oil thickens to protect the engine. This is how the motor oil gets its name; by displaying the two viscosities.

For most motor oils on the market today, their weight ratings come in the form of two numbers. The first, followed by a “W”, is the winter rating. The second, typically a much higher number, is the SAE standard rating for maximum temperature performance. So, if motor oil now changes based on the seasons, which one is the right one to buy? According to the SAE, motor oil, like this Valvoline oil rated at 10W30, is designed to stay fluid up to –30 C, while continue protecting the engine up to 100 C. It’s ideal for most temperate climates.

There are other factors for how hot motor oil gets; like speed. Track enthusiasts may find their engines producing a lot of heat, and the oil in their motor needs to be rated to handle that. Lucas Oil has formulated a synthetic oil with an SAE rating of 20W50. It should handle high heat and some cooler temperatures well.

Synthetic oil starts out the same way as conventional oil, but it’s then refined down to the molecular level. Manufacturers then mix in synthetic addidtives, which help the oil meet performance and lifespan requirements. Mobil is a popular choice among OE vehicles, and their 0W40 full synthetic has excellent multi-viscosity ratings. Every engine is different, and most vehicles have been engineered to use a specific kind of motor oil. Refer to your user manual for the SAE rating which best fits your vehicle.


Do You Really Need to Use Heavier Oil in Summer? [Ben Wojdyla] Popular Mechanics, July 2, 2012. 

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1 Comment

DoubleCoppers says:

It’s not true that all synthetic oils are “just refined further than conventional motor oil.” The best synthetics are made (i.e., “synthesized,” hence the name) from ethylene. They were never in the ground as crude oil, they are all straight-chain molecules (compare to “branched-chains,” later), and are completely pure. By contrast, “dinosaur juice” came out of the ground, and even after the extended refining process, can contain other compounds (such as branched-chains and aromatics) that pass through the refining process simultaneously with the desired oil molecules–but these other compounds are *not* as heat-resistant as the straight-chains produced synthetically. The branch-chains and aromatics break down at lower temperatures than true synthetics, and form the acids that corrode the engine, while also losing their desired viscosity rating. The only reason these “highly refined” oils are allowed to call themselves synthetic is b/c several oil companies pushed a lawsuit through the court system and buffaloed a judge (not a scientist, and definitely not a chemist, chemical engineer, or petroleum engineer) into thinking it was “close enough”…. so they could use the cheaper and easier-to-produce dinosaur juice, but still use the term “synthetic.” I only use oil that is true synthetic, like AMSoil.