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Small engine and synthetic oils

After reading about the perils in mixing different oils to use up odd qts. left over, someone suggested to use the left overs in small engines. I think that that is a splendid idea, however is there any info as to how these small (usually aircooled) engines fare with synthetics? I can’t think of any good/logical reason why they wouldn’t do just fine. Any thoughts on this matter?

I do not see anything wrong with it and won’t hurt anything, remember air cooled engines run hotter especially in the summer months, and synthetic oil can withstand more heat before breaking down…I would not extend oil changes though, my 23 year old Craftsman lawn tractor is still going strong doing this. I think the deck is going to rust out before the engine goes…A lot of engines will last just as long with regular dino juice as they are not used like a car engine that runs everyday…You cut the grass every week that takes a half hour or so, and in the winter hardly used except here in southern Florida where you may have to clip it every few weeks but the grass does slow down in the winter here. Just use a good quality oil what the manufacturer advises. If you won’t use it in your car don’t use it in you air cooled engines.

One thing, if the engine comes with a container of oil, use that first. most new engine manufactures recommend changing that oil after the first 5 hours of use…Then use what you want. When I buy my next lawn tractor will use all dino and in 23 years will let you know the results ! will be 88 years old then LOL

I look at it like this.

If the oil is too iffy to put into my vehicle, then isn’t going into any of my other engines.

Oil is oil, and an engine is an engine.


Many small engines (ie lawn mowers) really need 30W straight weight oil. Putting a 5W-30 or 10W-30 multi-weight synthetic oil into a lawn mower designed for straight 30W oil will not work well. The synthetic will thin out and the motor could be damaged. Since I’ve never heard of straight 30W in a synthetic oil I’d not use a synthetic in an air cooled small engine.

I have a Troy-Built generator with an eight horsepower Briggs and Stratton engine. If the generator is going to be used year round, the manual calls for 5W-30 synthetic oil. For summer use, it recommends 30 weight oil. The small engines on my mowers have different viscosity specifications for cold weather operation than for summer operation. Since I don’t mow in the snow, I use straight 30 weight oil in my mowers. I imagine that my mowers would work o.k. on synthetic 5W-30. I have seen two small engines ruined when the owner used 10W-30 dino oil in the summertime. If you are going to use multi-viscosity oil in an air cooled engine, at least be certain that it is synthetic.

Just check your manual. It will say whether synthetic is OK and what weights for what temperatures. You don’t necessarily use the same weight dino oil as synthetic though so check your manual or give the maker a call for sure. Some of my older manuals don’t address synthetic because it wasn’t available then, I did use it in an old rider once that sat outside and was rope start. I used it to make it easier to start in the winter. I use dino oil though in everything except the car that calls for 0-20. I stock about 5 different weights of oil for cars and small engines so its just a lot easier to use what is called for and not mixing anything.

One more thought if your engine requires 30 w straight oil you could “possibly” use the 20 w 50 racing Mobil 1 oil in an air cooled engine…These air cooled engines will run ok on this…I have been using Mobil 1synthetic 10w 30 in my 89 Mustang GT and lawn tractor for 20 + years without any problems even in hot Florida. Engines starts right up and not a puff of smoke out of the exhaust and no usage of oil between changes…

I have yet to have an engine failure in ANY 4 stroke small engine including outboards, lawn mowers, generators, snow blowers etc, many of which have lasted 20 plus years. I have always used 10w -30 or 5w-30 automotive motor oil…or any motor oil lying that I used in my cars or tractor, including synthetics. The oil was always changed once a year and in non commercial used, they will last a life time. Now, if they are used daily in commercial use, I would definitely use the exact oil recomended which may just be 30 weight. Changing the oil frequently in these motors without filters is much more important than using 30w oil IMHO. Use the synthetic…don’t fret unless you own and maintain a cemetery.

Air-cooled engines love synthetic oil as long as there is a “30” in the viscosity number…few small engines require straight 30 weight…Most specify 10-30…

@Caddyman–things must have changed since my mowers were manufactured. One mower was made in 1988 and has a Tecumseh engine and the other mower was made in 1992 and has a Briggs and Stratton engine. I did have to put a new short block on the 1992 mower because the engine was burning oil and fouling the spark plug. I used straight 30 weight and changed the oil every 50 hours as per instructions in the manual. I do use that mower quite a bit. I would have replaced the whole mower, but it has a cast aluminum deck and is strictly a mulching mower. It has two blades on the shaft at right angles and is wonderful for mulching leaves. I keep it going because I haven’t seen anything else on the market like it.

Our trimming mower bought last year, has a B & S engine. The owner’s manual specifies synthetic or non-synthetic high detergent premium quality SG. SF or better oil; mentions the synthetic first 10W-30 is recommended for general, all temperature use. 10W oil is good from -5 to +32F. 20 is good from 15 to 75 F. 20W is good from 20 to 75F. 30 is good from 50 to 100F. 40 is good from 95 to over 100F. 20W-40 and 20W-50 are good from 15 to over 100F. 15W-40 and 15W-50 are good from 0 to over 100F. 10w-30 is good from -5 to 95F. 10W-40 is good from -5 to over 100F.

Mmost of mine call for straight 30 wt in the summer (above 40 degrees) and 5-30 or 10-30 in the winter, below 40 degrees. I’ve got only one Techumseh and the rest are Briggs and Suzuki/Toro.

I wonder if there is any advantage to using detergent oil in a small air cooled engine. These engines don’t have hydraulic valve lifters. Back in the 1950s, we used non-detergent 30 weight in small engines. In fact, I used non-detergent oil in my 1947 Pontiac and my 1948 Dodge both of which had 6 cylinder flathead engines… My dad had a 1963 Studebaker Lark with an overhead valve V-8. It had solid tappets and the owner’s manual specified non-detergent oil. Detergent oil is more commonly available than non-detergent oil today, so it does have that advantage.

I decided to try synthetic this year in my mower, which is about 10 years old, and purchased used. It has a B&S 6.5 HP engine I think. I’m pretty sure it calls for straight 30 weight, as most every mower seems to. I decided to try 10W30 Amsoil in it.

All I can go by is what I subjectively notice: The mower seems to run quieter and smoother. It seems “happy” and just purrs on the stuff. It sounds to me a little less labored. I still get the same puff of blue smoke when I first start it, so it probably has a little ring wear, but it’s always done that. It has always started on the first pull, unlike every Tecumseh engine I’ve ever owned.

I have a 25yo mower I use to mow my duplex. It has a 3hp B & S engine. Says to use 30 weight oil. I’ve been using multi-viscosity oil since I bought it. Use to use 10w-30…now I use 5w-30. I’ve been using synthetic oil for my lawnmower and snow blower for years. They love it.

After reading about the perils in mixing different oils to use up odd qts.

Perils?? Could someone show me ONE peril with mixing different oils?? There might have been SOME truth to this 40+ years ago…but NOT today. But I guess it’s hard for a good rumor to die.