Does SAE viscosity even matter in a splash lubed engine?
I'm thinking that it really doesn't.
What do all of you think?
depends if they call for sae 30, and its 100f out in texas sae 40 wont matter, at 0f in ohio it may.
that all being said I use 15w40 in all the tractors, and usually 10w30 in the lawnmowers.
snowblower usually gets 5w30 or 0w30
The most important aspect of a lubricant is viscosity! This is tribology 101.
Yes, viscosity grade matters in a splash lubed engine. It matters from a lubrication aspect and it matters from a heat dissipation aspect. Use what the manufacturer specifies.
I believe that B&S's oil slingers are designed for 30 weight oil at normal operating temperatures.
You want a multi-grade oil like 5W30 synthetic so that the slinger will work during cold temperature start-ups through engine warmup.
Okay, now that everybody has put in their two cents, I'll clarify what I originally meant.
In 1997, I bought an MTD mower on clearance from Target for $70.00.
Over the years, I ran everything, including HD30, HD40, 10W-40 and mostly 20W-50.
The Tecumseh endured for what I calculate as more than 400 hours based upon the size of our yard, the length of time it takes me to mow it and the number of years I used the machine. Just for reference, nobody else in our subdivision push mows their yards. Everybody else uses a lawn tractor or ZTR. It still ran when I put it on the curb on trash day, although the mower as a whole had served its purpose and owed me nothing and had enough little issues that it was time to let it go.
It didn't last long on the curb either.
The viscosity isn't the primary issue with splash lubed engines. The primary issue is with maintaining proper levels, not operating it with water or debris contamination and then proper viscosity is on the back burner. Anything up to 40 weight is acceptable to most splash engines with a few exception to high weights when very high operating or starting temperatures are experienced.
30 or 40 weight is the most commonly acceptable weights, but I actually want to test a Briggs 5hp flathead with a 5W-20 to see what actually happens. I have one that is about 15 years old and was probably on its original oil when I got it and want to see what kind of protection and performance I can find with a synthetic 20w of some kind. I'm sure it will be fine and may even save some fuel in the process. Just my curiosity and free equipment giving me some ideas.