Is 0W-20 Oil Too Thin? A Four-Viscosity Bench Test

If your car calls for 0W-20, you have probably noticed it is thinner than the oil your dad's car used, and you may have wondered whether that thinness is actually good for the engine or just good for the EPA's fuel economy numbers. Automakers moved to thinner viscosities specifically to squeeze out mileage gains, and the marketing around 0W-20 leans hard on "advanced protection" language without ever showing the tradeoff on a bench.

One hands-on test actually put 0W-20 head to head against three other viscosities of the exact same oil line, isolating viscosity as the only variable. That is the closest thing to a controlled answer this question is going to get, and the results are a genuine tradeoff rather than a clean win for either side.

What the testing showed

The numbers below come from Project Farm, who tested four viscosities of Pennzoil Platinum full synthetic oil (0W-16, 0W-20, 5W-20, and 5W-30) side by side on identical rigs. You can watch the full comparison on the motor oil viscosity test. This is a single-brand viscosity comparison, not a multi-brand shootout, which is exactly what makes it useful for isolating what 0W-20 actually does differently from other grades.

Important context up front: this test only had four products in it, all the same brand, so there is no "winner" among competing brands here. The point of the video was to settle whether thinner oil sacrifices protection, and the host declined to declare an overall winner, landing instead on "use whatever your manufacturer specifies."

How 0W-20 performed against its stablemates

• Room-temperature flow race (all four oils simultaneously): the 0W-20 finished 2nd, just barely ahead of the 5W-20 and just behind the thinner 0W-16, in both the uncooked and heat-exposed runs.
• Thermal breakdown/evaporation test (200g heated to 410F for 2 hours): the 0W-20 lost 3.97 g, the second-worst evaporative loss of the four, though the differences between all four grades in this test were relatively tight (3.59 to 4.36 g).
• Cold flow at negative 40F, fresh oil: 1 minute 54 seconds, barely ahead of the 5W-20's 1:57, and dramatically faster than the thicker 5W-30's slowest-of-the-four result.
• Wear scar (lubricity) test against 5W-20: the 0W-20's wear scar was about 7 percent larger than the 5W-20's, meaning slightly less wear protection in that specific pairing, though the notes describe it as "performing almost the same" as the 0W-16 at the start of testing and "definitely more wear than the 5W-30."

The clearest single finding: 0W-20 and 5W-20 were extremely close across almost every test, closer to each other than either was to the 0W-16 or the 5W-30. That matters, because those two grades are the ones most commonly cross-shopped by owners staring at a dipstick cap.

A separate multi-brand motor oil test that included 0W-20-rated oils, such as Honda's Ultimate Full Synthetic and Toyota's factory oil, showed real spread between brands within that single viscosity class. Honda's oil had the worst evaporative loss of six oils tested (7.72 g of 200 g) despite finishing second on wear protection, while Toyota's oil had the weakest additive package and the lowest total base number of the group. In other words, viscosity is only one variable; brand and additive package still move the needle a lot within a given grade.

How to read this for your own purchase

The viscosity test's own conclusion is the most useful takeaway here: it explicitly declined to name a winner, and its closing advice was to run whatever viscosity your engine manufacturer specifies rather than chase a "better" grade based on a lab result. That is worth taking seriously, because oil viscosity is engineered around specific bearing clearances and oil pump specs in a given engine design, not a universal performance scale.

If your manual calls for 0W-20, the testing gives you real reassurance rather than blind trust: it flowed fast in the cold, kept pace with 5W-20 across nearly every category, and its slightly worse wear-scar number relative to 5W-20 was described as a small gap, not a dramatic one.

If you are choosing between two 0W-20 oils from different brands, the viscosity itself will not tell you much, since it is held constant. Lean on brand-level results instead: the multi-brand motor oil test showed a nearly 25 percent spread in evaporative loss between the best and worst oils tested, all full synthetic, all similarly marketed.

Do not "upgrade" to a thicker oil than specified hoping for extra protection. The video's data shows that tradeoff runs both ways: thicker oil resisted evaporation and wear a bit better, but flowed noticeably slower in the cold, which is exactly the moment an engine needs oil moving fast to protect start-up wear.

A few rules the data supports regardless of grade:

• Follow the cap, not the lab. Every conclusion in the sourced test points back to manufacturer spec as the deciding factor.
• Additive package varies more by brand than by viscosity. The multi-brand test showed bigger spreads in detergent, dispersant, and TBN between brands than the viscosity test showed between grades.
• 0W-20 and 5W-20 are closer than they look on paper. If your engine can technically run either, the bench numbers do not show a decisive reason to prefer one over the other.

Want to see how full synthetic oils compare across brands rather than viscosities? Browse the rest of the engine oil and fluids tests for the complete breakdown.