can car oil go in a lawn mower

[DeBrynlee]

No, you should not use standard car engine oil in a typical lawn mower. The engines operate under completely different conditions, requiring oils with specific additive packages. Using car oil can lead to inadequate lubrication, increased engine wear, and potentially severe damage.

The core difference lies in the engine design and operation. Most lawn mowers use air-cooled engines that run at a consistently high temperature and RPM. Car engines are liquid-cooled, maintaining a more stable, lower temperature. Car oils contain detergents and dispersants designed to handle the byproducts of combustion in a closed, complex system with an oil filter. Lawn mower oils are simpler, as the mower's engine lacks an oil filter; contaminants are suspended in the oil until it's changed.

Using car oil in a mower can cause two major problems. First, the high detergent level can create excessive ash deposits on the mower's hotter combustion chamber, leading to pre-ignition or "engine knock." Second, the oil may not have the necessary high-temperature additives to prevent breakdown under the intense heat of an air-cooled engine, resulting in reduced lubrication and accelerated wear.

The safest approach is to use an oil certified for small engines. Look for the API (American Petroleum Institute) service classification on the bottle. For most 4-stroke lawn mowers, an oil marked API SJ, SL, SAE 30, or 10W-30 is appropriate. Always consult your mower's owner's manual for the manufacturer's specific recommendation, which considers your local climate.

Engine Characteristic	Typical Lawn Mower Engine	Typical Car Engine	Implication of Using Car Oil in Mower
Cooling System	Air-cooled	Liquid-cooled	Car oil may break down under higher operating temps.
Operating Temperature	Higher and less stable	Lower and more regulated	Incorrect viscosity can lead to poor lubrication.
Presence of Oil Filter	Usually no	Yes	Car oil detergents are unnecessary and can cause ash deposits.
Common API Service Class	SJ, SL	SN, SP (modern)	Modern car oils lack additives needed for air-cooled engines.
Typical Oil Weight (Moderate Climate)	SAE 30	5W-20, 5W-30	Wrong viscosity affects engine starting and protection.

[VonAustin]

I learned this the hard way. My neighbor, who's a small engine mechanic, told me straight up: car oil will gum up a mower engine over time. He said the oils are formulated differently because mower engines get much hotter and don't have oil filters. You're better off just buying the small bottle of lawn mower oil. It's cheaper than a new engine. Trust me, it's not worth the risk.