Every DIY motorhead has an opinion on oil. Our absurd hot takes can range from pouring Walmart-brand diesel grade in every engine we own to speculation on oil “conspiracies,” such as European cars that go 20,000 miles between changes. But Lake Speed Jr. doesn’t speculate.

Lake Speed Jr. holds multiple certifications with the Society of Tribologists & Lubrication Engineers. He formulated oil for multiple NASCAR teams, including the oil Joe Gibbs Racing ran while winning the Daytona 500.

Speed founded SPEEDiagnostix and continues testing various oils. He shares his findings on his YouTube channel, The Motor Oil Geek. The channels motto is “science, not speculation.”

General Motors Has a Change of Heart — or at Least a Change of Oil

In a recent video, Speed called out a motor oil myth circulating online. It goes like this: “You can’t use a viscosity higher than what the OEM recommends.” He claims General Motors proved this myth false when it changed its recommended oil viscosity in the wake of an engine recall.

Speed’s referring to the headline-grabbing recall for the 6.2-liter “L87” V8 in full-size GM trucks and SUVs. General Motors is urging dealerships to inspect 597,630 vehicles for deteriorating crankshaft main bearings. But even if the crankshaft and connecting rod assembly passes muster, GM is telling dealerships to swap the V8’s 0W-20 oil out for 0W-40.

Why? Lake says the change is “to increase that bearing film thickness to protect those bearings and the crankshaft, you’re increasing viscosity…If you don’t have enough film thickness, you’re going to have a bearing failure.”

“GM is using tribology to solve the problem by increasing bearing film thickness to counteract a problem they have with the bottom end. They’re using it as a Band-Aid.”

— Lake Speed Jr., Founder SPEEDiagnostix

Lake claims the thicker oil better protects these bearings, especially if the engine is under load and running at higher temperatures. But that just begs another question. An automaker can’t put a price tag on building a reputation for durability. So why wouldn’t GM have thrown 0W-40 in these engines at the factory?

The 0W-20 Oil Myth

Luckily for us, Speed also conducts oil tests for OEMs. “We saw that — with that test we did with GM and Oak Ridge — putting a 0W12 in that engine that even though it called for a 5W30, we improved the fuel economy in the EPA drive cycle.”

Why would an oil swap improve mileage? “That lower viscosity is less drag. That’s going to be better fuel economy.” Lake explained that the lower viscosity especially helped with around-town MPG, a strict metric automakers sometimes struggle with.

Could the recent swap to lower viscosity oils be just to meet tightening EPA regulations? Speed thinks so.

“In other countries where there’s not the EPA and there’s not a corporate average fuel economy target that needs to be hit, the exact same engine somewhere else in the world, the owner’s manual will call for a higher viscosity oil.”

Now, the cat’s out of the bag. GM’s admitted that a higher viscosity oil will protect components such as main bearings better than 0W-20. But even with 0W-20 potentially leaving engines at risk, lower viscosities are coming. All in the name of MPG. Speed says, “The reason for that change in going to the 0W20, 0W16, 0W12, 0W8 — like in my daughter’s car — is because of fuel economy.”

I argue we need a more efficient auto fleet. But we should do it by driving smaller vehicles and reliable plug-in hybrids. A short-lived engine is a net negative for the environment, whatever its MPG.

Should You Thicken Up Your Oil?

So should you drain your 0W-20 and pour 0W-40 in your engine? Not necessarily. Speed says there are multiple potential downsides.

“You might make the engine run hotter. Thicker oils typically make the engines run hotter. We’ve seen that in the dyno tons of time.” The result could be more engine wear, not less.

In-line with his “science, not speculation” motto, Speed recommends two separate oil analysis after running two separate thicknesses to test which one equals “lower wear metals in the used oil samples.” See his testing process in the video below: