Lawn mower oil

My lawn mower manual asks for SF grade 10 W 30 oil. The Oil I bought does not say SF class and the person in the Autozone does not k now what SF means. Please explain what really SF means and is it sold anywhere?

You don’t say what this mower is but most people just buy 10w30 Lawnmower Oil . That is what it says on the bottle . That is what I have done for years and the engine usually outlasts the mower frame.

SF is an obsolete API oil classification grade from the 1980’s, the current grade is SN, use the current grade.


Newer is better, if that isn’t clear. SG replaced SF, SH replaced SG and so on to SN.


You will find it in hardware stores like Home Depot or Lowes and maybe in the garden section of Walmart. It costs more and usually sold in 20 oz bottles instead of quart bottles. You pay more to get less. Make sure you get 4 cycle oil and not 2 cycle oil. It is also sold under brand names like Briggs & Stratton.

Why would you buy it? It has two chemicals not found in today’s oil, Molybdenum Disulfide aka Moly-B and a zinc/phosphorus compound known as ZDDP. These increase the lubricity of oil but have been removed for modern vehicle engines because they degrade catalytic converters.

If it’s a Briggs, they now say you can use 10-30 Synthetic year round in everything. I use Mobil 1 in lawn mowers, snow blowers, generator, etc. all the time. I think you have an old manual or it’s one of those Liquid Crystal engines.

I wouldn’t worry about the SF, probably none of that on the shelf anyways, much newer oil in stock now. But it is very telling of the knowledge of the Autozone employee, and any training they do not receive.

I have to wonder how old the OP’s lawnmower is if its manual mentions an oil classification from 3 decades ago.

Except at Dollar General maybe…weren’t they selling off really old out of class oil not too long ago?

I’d have to search for that but I don’t think it was so outdated as to go back as far as SF. And even they probably don’t have anymore of that old stock. But maybe, it is Dollar store after all.

My old lawnmower which I bought in 1992 called for heavy detergent straight 30.weight oil. Several years ago, the oil consumption inceeased to the point where I was almost asphyxiated when I would mow. As an experiment, I bought a quart of house brand 10W-30 full synthetic oil at my local Rural King farm store. House brand 30 weight was $1.79 a quart. The full synthetic was $2.79 a quart. I decided to gamble a.dollar on the full synthetic. After two seasons, the oil consumption and blue smoke is gone. I was going to junk the mower and buy a new one. I now have no need for a new mower.
Oils have improved over the last 25 years. I remember when the SF designation was the newest oil. I remember well the SA and SB classification from the 1950s.

I think that the junk oil that they were selling was actually SA-spec oil.
I would only use garbage like that to lubricate hinges.


:open_mouth::open_mouth::open_mouth: SA?! I wonder what government surplus warehouse was storing oil that old waiting for a sucker to pawn it off on…

Okay, I guess that I exaggerated… a bit.
The verbiage (in tiny print) on the bottles states that the oil shouldn’t be used in cars built after 1988.

Which specification was the one in effect in the 1988-89 era? Obviously it wasn’t SA, but I don’t recall which old specification was in effect in those days.

SF is engines built after 88:

This is what it says for SA, though:

CAUTION : Contains no additives. Not suitable for use in most gasoline-powered automotive engines built after 1930. Use in modern engines may cause unsatisfactory performance or equipment harm.

I knew that I recalled reading about SA-spec oil that was still being sold a couple of years ago.
Here is a warning from the folks who help to come up with the oil classifications:

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Back in the 1950s, I used SA 30 oil to mix with gasoline for the two stroke LawnBoy mower we had. The ratio was 16:1–1/2 pint to a gallon of gasoline.
The SA was not a heavy detergent motor oil and worked well for the time period.
Now the ratio is 50:1 for many two stroke engines and special two stroke oil is available.

Every few years the oil industry upgrades its engine oil specifications to meet new car engine requirements. The spec started at SA, then switched to SB, SC, etc. Sometimes this is referred to as the “S-grade” for the oil. The switch from SE to SF happened in the early 80’s as I recall, now has progressed to SN. A new oil spec is designed to be backwards compatible to all the older specs. Therefore if your lawnmower requires SF, then anything from SF to the current SN should work well for you. The letters “SF” or “SN” appear on the oil can, usually near the round API seal. Any major oil brand like Penzoil, Valvoline will have the S-grade clearly printed on the can or bottle. The complete oil specification for an engine also includes the viscosity rating (e.g. 10W30) and whether it is synthetic or not.