2-stroke mix in a 4-stroke mower

[JHZR2]

Hi,

The end of the mowing year is near, so we didnt buy any more 87 octane gas for the mower. We needed to mow yesterday, so the fiancee added some 40:1 mixed 89 octane gas to the very small quantity of gas that was in the lawnmower tank already. She didnt fill it all the way...

It ran perfectly, I think it smeled a bit more than it usually does (usually I cant detect the smell of the exhaust from our mower), but there was no smoke or any other bad signs.

I was upset that she put this fuel into the mower, but it worked fine, and was the thing to do in a pinch. I will be changing the oil for the year in a few weeks (when I run the mower out of gas for good), but is there any possible issue with using a 40:1 mix in a flathead 4.75 hp (gross) B&S engine?

Thanks!

JMH

 

[CBDFrontier06]

It probably just lubricated your top end....it may have even like it. The only downside I can think of is its affect on the spark plug and the exaust system, but the engine may run hot enough that the effects may be nil. I know the spark plug in my sister-in-laws 2-cycle trimmer is always cruddy...not sure if a 4-cycle would react the same way.

 

[tmorris1]

I have run mixed gas in my engines in a pinch and have never had issues. I have ran out of regular gas and used the weedeater can to get the lawn done. If you did it every tank for the entire summer you may get some carbon buildup or something, but nothing to worry about.

 

[Blue99]

Minor amounts of 2 cycle mix won't hurt a B&S engine.

However, every component of the 2 cycle oil must either burn or be exhausted from the cylinder. Typically, the metallic additives,(Calcium detergents & Moly or Zinc anti-wear) will eventually form deposits on the spark plug & exhaust valve.

So the little lady should go easy on the mix gas!

 

[80caprice]

Didn't hurt a thing..... I once had a gallon of 40:1, old... maybe a half a year old that set through the winter and a old b&s that was empty... threw it on in there and it ran fine...
The spark plug may get a little crudded... my 2 cycle plugs have always stayed nice and clean running 40:1 though... piston and exhaust port as well and I have it set richer then factory.
That old engine though used oil anyway.... so of course the plug on mine got crudded, it was a combo of leaky valve stems and a broken oil ring.

 

[Cujet]

In fact, the use of 2 stroke oil in 4 stroke engines has been proven to help valve and valve seat life. The jury is out as to whether it helps or not with ring life. But I suspect it also helps in that department.

Chris

 

[UncleS2]

A tank of mixed gas won't hurt a thing, don't worry. Your lawn mower's fine, you need do nothing extra to it. If you used mixed gas all the time, at worst you might have to change/clean the spark plug a little sooner.

A local lawn care guy makes it a point to run at least one tank of mixed gas weekly through his 4-cycle mowers- he's convinced it helps engine life, sure doesn't seem to hurt.

One local small engine shop/outdoor power equip dealer(now closed) ran mixed gas, super unleaded only, in *everything* they sell or service. When I asked about this years ago, the owner said it ran just fine in every small engine he'd ever seen, whether 2-cycle or 4-cycle, and was a heckuva lot cheaper than burning up an engine in a new Stihl chain saw.