Unbelievable…60 replies when one would do: “Use 30 weight.”
Ya gotta love this site (not sarcasm…it’s why I stick around).
;-]
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FYI, the W has not always meant winter. It used to mean weight. Here is a pretty good explanation, a little challenging to follow this late at night, but accurate as far as I can tell.
Most bike manufacturers specify motorcycle only multi grade oils that have additives that car oils don’t have.
For motorcycles that use wet clutches, look for “JASO-MA” on the oil can. I have used mostly Shell Rotella T6 5w40 in my last two motorcycles with excellent results, if you look at the label, it has the “JASO-MA” rating on the list of ratings. And it’s somewhat more economical than the oils that have a picture of a motorcycle on the label.
Is this a trick question? … lol … Since the lawnmower manufacture recommends SAE 30 oil, use that. I think SF grade is from the early 80’s, so any oil you buy now that’s SAE 30 should be ok.
Also, it’s additives that are left out, particularly the friction modifiers in modern energy saving oils. Not only do they make clutches slip but also the one way sprag clutches in the electric starter drives.
Once again if its a Briggs (or others 'cause they aren’t much different taken apart), here’s the chart. I use 5-30 Mobil 1 year round in everything. Makes it simple.
Went to Home Depot this evening and got great customer service. An employee used a reference manual to look up the correct oil, air filter, and blade per my mower’s model number.
After looking at the original blade on the mower which has a significant chip in the edge from accidentally hitting a corner of concrete support pad for one of the support pillars of the house deck, I decided $12 for a new blade is my best plan rather than try sharpening a blade with a deep chunk missing from the edge.
If I can manage to do the work myself for $37 supplies, I can save over $100 in labor and pick-up and delivery. And have learned how to manage something new for myself.
Now I just have to follow instructions in the user manual. And have enough hand strength to get it done. 
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Never expected my simple lawn mower question to spawn so much discussion. But I have truly enjoyed reading all the responses and learning about oil varieties.
Thanks everyone for the help and for putting up with me.
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@Marnet Way to go! Maintaining your lawn mower yourself not only saves money but saves time as well. I can service my lawn mowers in less time than it would take to load then in the van, take them to a shop, then when the equipment is ready, load the mowers back up and bring them home.
use the straight 30 weight oil the 5w30 is 5 weight oil that can take 30 weight oil abuse. the 10w30 is 10 weight oil that can take 30 weight oil abuse. most air cooled engine take even 40 weight oil but oil makers are going away from 40 weight. my corvair takes 40 weight oil. anything lighter and it just evaporates away.
just so you know an air cooled engine runs way hotter that a water cooled evhing. what would you do if your car’s temp gage got to 325 degrees? my corvair is just right at that temp just to give you an idea of the operating temps of air cooled engines
Remember that these mowers are air-cooled and any multi-viscosity oil will tend to shear down faster than a straight weight. Oils sold for small engine use are made with this in account. They also have a higher amount of anti-wear additives such as zinc that would foul the emissions systems in an emissions controlled engine.
Some of my engines are run in colder weather. The manuals for some suggest 30W in hot weather, 10W30 in warm weather, and 5W30 synthetic in cold weather. Others suggest only 30W or 10W30. I got sick of having all these oils around and did some research. I have settled on the Rotella T6 synthetic 5W40 and haven’t been happier. All the engines with hydraulic lifters seem to eat this stuff up and all the old school flat tappet solid lifter stuff does fine as well. The Rotella T6 is a heavy duty oil and seems to withstand all the abuse I put my mowers and equipment through.
I once changed an older L-head Tecumseh from this to a 10W40 that I bought out of convenience. That engine started smoking and having all kinds of blowby. You could hit a tough patch and it would just bog down and fog the area with smoke. I figured the engine was just wearing out but all this stopped when I changed it back to the Rotella T6.
Then I had put that used 10W40 oil in a clear plastic container because I didn’t have a bottle for it at that time. I came back with a bottle a while later and found that all the sludge had settled to the bottom and the oil on top was perfectly clear! Not all oils are made equal! The oil was STP high mileage from Autozone which I figured would be good in a mower but I guess not.
You could also use an ATV/Motorcycle oil in a mower. I ended up being given some of this and wanted to use it up. Again, it has higher anti-wear additives and is formulated for hotter running air-cooled engines so is a good choice for mower use.
Marnet, I think the community has done it’s usual good job and given you the right answers. If the manufacturer specifies 30W oil then use that oil. They know best. In the event you don’t have straight 30W you might use 10W30. If your mower is older and is burning a little oil then I would use 10W40 oil. The API is a good classification that you should pay attention to.
Good luck in the future.
Marnet, has oil, filter and a new blade so I think we are done here.
In what chord were they singing?
Yep, y’all’s work is done and done exceedingly well. My thanks!
Just an aside…l have never had a small engine failure in a lawn mower, all of which lasted 15 to 20 years in residential use…as long as you regularly change the oil regardless of the weight if it’s for non commercial use and used just weekly. HD use I’d definitely use straight 30w. The deck rusts first if not aluminum or something else fails. In other words, you can’t go wrong. 