What weight of oil to use in my generator?

 “I had always heard to use SAE-30.  I looked in the manual and they give SAE-30 as an option...but also 5W30 and 10W30. They warn that using SAE-30 with temps below 40 F could cause damage.  They are just not real clear .....help!

 NYS SITEPOWER Generator Tech says:

Lets start with straight motor oils here. We'll take SAE-30 weight oil for a first example. Good strong oil. Works great in the summer and on a hot running engine (which most air cooled engines are). This is why it's the recommended oil for lawnmowers and such. It doesn't break down when hot and provides excellent lubrication.  But…

…  SAE-30 flows like tar when its cold. Cold like a January morning in Upstate NY. In fact, many times the oil pump can't suck it up, and the engine runs without oil for a while until it warms up the oil, and that isn’t good!  Many engines have been damaged from this back in the day.

So engineers came up with the multi-viscosity stuff, like 10W-30. It's still 30 oil, but when it’s cold outside (like winter time, hence the "w"), it flows like a 10 oil. Magic! So on that cold January morning, it flows like pancake syrup, not tar. The oil pump can move it through the engine, and it doesn't starve for lubrication when started up.

Ah, but there is a downside to 10W-30 oil, it's not as "tough" as straight 30. It will break up molecularly more easily than the straight 30. So in really hot and harsh applications, like a lawnmower in the summer, it's not as good. It's generally "good enough", but not quite as good.

You go up and down this viscosity index depending on various things, like weather conditions, application, etc. A lawnmower in Florida runs a whole lot hotter than a car up in Alaska. So you'll need to adjust viscosity accordingly. Looking at start-up conditions, as well as running conditions.

So your generator, can it run on 5W-30 or 10W-30? Most likely.   Almost anything can. But, if it's a hot running air cooled engine, and you use it in the summer, a straight 30 oil would be better. If it's going to be used in the winter, you'll want a 5W-30 oil instead – this is especially important in our area in the winter months to ensure easy & reliable starting.

Do I apply this to my own stuff?   You bet.  My snowblower has 10w-30 in it, so I can start it up in the winter. My lawnmower has straight 30. It doesn't get started in the winter, and runs hard and hot in the summer.