Spent the afternoon flushing the mower and saved the engine

My neighbor did something similar with an old Toro Recycler a few summers back. He didn't even realize what happened until the engine started belching thick white smoke halfway through the front yard. He was convinced he had blown a head gasket or cracked the block, but it turned out his teenager had topped off the oil reservoir with the weed whacker mix from a red Blitz can. When we drained it, the stuff that came out was basically gray water. I had him do a double flush with some basic 10W-30 Pennzoil we had in the garage. We ran it for maybe five minutes each time just to get the temp up and circulate the detergent. We actually saw a few tiny silver flakes in the second drain, which had us worried about the bearings, but we swapped in some Briggs & Stratton synthetic and hoped for the best. That was three years ago and that mower still starts on the first pull every Saturday. These small engines can handle a lot of abuse as long as you catch the mistake before the heat causes a total seizure. It is a messy lesson, but way cheaper than a trip to the local power equipment dealer for a replacement.

The smell of that 2-cycle oil actually lingered in my garage for a week even after I'd cleaned the mower deck. My biggest concern wasn't even the lubrication, but how that fuel-heavy mixture affects the plastic dipstick and the breather tube. On my Troy-Bilt, the mix actually caused the breather to clog up with a wierd milky sludge about two mows later. I ended up having to spray a ton of carburetor cleaner through the upper assembly to get it to stop surging. Draining the oil is the first step, but keep an ear out for any hunting or surging in the RPMs. Sometimes that thin mix gets pushed up into places it doesn't belong through the crankcase ventilation system, and that's a whole diferent headache to clean out. I'd definitely check your air filter too; if the mower was tilted or the mix splashed while they were cutting, it coud be soaked in oil now.

You definitely dodged a bullet there. Since that gas likely ate into the surface of your bearings, you need to be worried about long-term friction. When I had a similar scare with a pressure washer, I started adding about 20% Lucas Oil Heavy Duty Oil Stabilizer to every fill. It clings to the metal parts much better than straight oil, which is huge if your tolerances got a bit loose from the 40:1 thinning.

It keeps the engine running cooler and quieter. Don't just trust a standard 10W-30 after a thinning event like that; the Lucas stuff gives you that extra cushion.