Does it hurt to mix different weights of oil?
Emily Sparks
Published Jan 14, 2026
The good news is that mixing different types of oil it will not harm your engine in any way in the short run. Most synthetic and semi-synthetic engine oils are based on regular oil and are compatible.
What happens if you mix oil viscosities?
It is always advisable to not mix motor oil brands, however, different viscosity grades of the same brand motor oil are compatible. Be aware that mixing viscosity grades will turn out a product that is different in viscosity than either what was originally in the engine or what was added."Is mixing different types of oil bad?
WHAT ABOUT MIXING ENGINE OIL BRANDS? Yes. It won't harm your engine to mix, for example, Quaker State® motor oil with Pennzoil, as long as the oil you use is the weight (or viscosity) recommended in your vehicle owner's manual.Can you mix 10W30 and 10W40?
Mixing 10W30 with 10W40Some say that mixing them is fine as long as you don't live in freezing weather. Even if you put together synthetic and conventional blends of these motor oils, they show no harm to your vehicle. However, this is true only if you mix in a quart of the other type to your usual engine oil.
Can I mix 5w20 and 10W30?
Notwithstanding the recommendations of the car manufacturer, mixing 10w30 and 5w20 will not cause any sort of harm to the engine. However, a few drivers claim that it is safer to combine two multi-grade or straight weight oils, rather than mixing multi-grade with straight weight oils.Will Mixing 10 Motor Oils Damage an Engine? Let's find out!
Can you mix oils of the same weight?
They're all pretty much made by the same companies in the same assembly lines anyways. Don't mix weights or synthetic and non synthetic. You'll be okay.Can you mix 5w30 and 0w20?
Yes, just that. Pennzoil Platinum is a thin 30 or Valvoline Advanced also in 5w-30. Both syn oils. If you are in that part of NorCal where it's truly -10 or more, consider M1 AFE 0w-30.Can you mix 5w40 with 15w40?
Mixing a dino with a syn, a syn with a dino, a 5W-40 with a 15W-40, and so on is fine. You aren't going to get an additive clash, the different base stock of x brand of oil won't sponteously combust with the other x brand of oil that you are blending it with and make your engine throw a rod.What happens if you use 15w40 instead of 5W40?
There is a single benefit to 15w-40 oils though, they will maintain their 40 weight operating viscosity longer than an oil that starts at 5w. This is not rocket science, it takes less friction modifiers to get from 15 to 40 than it does from 5.Is 5W or 15W thicker?
The 5W-40 will have a lower viscosity when the engine is started than the 15W-40; consequently the 5W-40 will start easier and lubricate quicker in the cold than the 15W-40. The American Petroleum Institute (API) defines minimum lubrication requirements for motor oil physical properties and performance.What is 15W-40 oil used for?
ADVANTAGE 15W-40 HEAVY DUTY DIESEL ENGINE OIL can be used with complete success in over-the-road diesel trucks, off-highway diesel equipment, farm tractors, and passenger cars and light trucks with diesel, turbo-charged diesel engines, or gasoline engines and is backward compatible with previous API Oil Categories.What happens when you mix oils in a car?
Mixing different types can destabilize your motor oil, reducing its efficiency and affecting your engine's performance. The smartest choice is to stick with the oil type and oil change intervals recommended by your car's manufacturer and visit your local car care experts for affordable services.What happens if I put 5W20 instead of 0W20?
0W20 vs 5W20 Fuel EconomyBoth 0W20 and 5W20 are low viscosity and high-quality synthetic grades that can massively optimize fuel economy. Their properties are the same when used in fair-weather temperatures. Likewise, there is little to no difference between the two versions when used in cold conditions.