Join Date: Feb 2013
Location: New York
Thanked 1,230 Times in 1,136 Posts
Lawn mowers aren't that picky about motor oil. Lubrication has come a long way from the 1960's and most mower engines are basically last century tech. I run diesel engine oil because it's robust and I buy it in large containers. If you've torn down old engines, you often see a ridge at the top of the cylinder due to wear, but you never see that anymore. 5W30, 10W30, SAE 30, etc. will all work fine as anti-wear, dispersant, and detergent additive packages are far far better than they were even 20 years ago. The only exceptions to that would be extreme cold and extreme heat conditions. Snowblowers start easier with synthetic 5W30, and on the opposite end of the spectrum, a generator running full bore all day in a summer blackout or a big V-Twin on a ZTR running in Texas heat will appreciate some nice stout Mobil 1 15W50 or the like. Modern oils will keep your push mower engine running long after the wheels fall off and the deck rusts out.
P.S. That Amsoil "Small Engine" stuff is super expensive but is great for engines that work in the heat all day (generator/commercial turf engine). I believe it's actually a monograde with no viscosity index improvers that has a base oil with a high enough viscosity index to meet the requirements for a multigrade.