SAE 30 Straight Or 10W-30?

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SAE 30 Straight Or 10W-30?

Steve Just a quick question about oil viscosity for my lawn tractor... The manual for my old MTD with a Briggs and Stratton 16 HP V-Twin strictly stated NOT to use 10W-30 because it could become too thin during high temperatures. It stated that only straight 30 weight should be used. Now, I have a new JD L120 with a Briggs and Stratton 20 HP V-Twin. It specifically states that 10W-30 SHOULD be used. Why is 10W-30 OK for one and not for the other? They are essentially the same engine, just different displacements. I have been following the instructions in the manual, but I was curious about the different reccommendations. Thanks!
thingy Yeah,,me too,,,,unless you were running it in the winter,,,you would think 30 weight would be just fine,,after all,,I believe 10w30 starts out as 30 weight with some kind of additives that make it go as thin as 10 weight,[don't know how that works],,,maybe they are getting better at making multi grade oils? makes you wonder about you car oil BEFORE they were getting better at it,,don't it? thingy
george I think that 10w30 starts out thin (10)
for easier cranking but gets thicker
with the heat.

Pete Sears also specifies 10W30 viscosity oil for their Kohler Pro engine tractors. This is the first time I see multi-viscosity oil specified for a small industrial engine. Everything else I own that has a small 4 cycle engine calls for SAE 30 oil (pushmower, edger, generator, string mower, tiller)

In my opinion, SAE 30 straight weight oil provides better protection for an engine that runs at full open throttle for long periods of time. This is exactly what lawn and garden tractors do. I own a boat with a Ford 302 cu in fuel injected V8. The recommended engine oil is SAE 30. This same engine is used in various Ford vehicles and the manufacturer specifies multi-viscosity oils for them. Marine engines are considered to be industrial engines because just like lawn tractor engines, are run at wide open throttle for extended period of time. This condition builds up much more heat and puts more demand on adequate oil lubrication.

In my humble opinion, you cannot go wrong using straight SAE 30 oil in your lawn or garden tractor, especially in warm climates like Florida. Most of these engines are air cooled and they run at wide open throttle almost continuosly.

Another example of SAE 30 oil requirement in an industrial engine:

2 1/2 ton Army truck (M35) with multifuel 478 cu inch straight 6 cylinder engine requires SAE 30 motor oil. This engine is built to run at wide open throttle for extended period of time. It is basically a diesel engine that can run on alternate fuels in an emergency. The oil capacity is 22 quarts top provide an adequate reserve.

So in summary, engines that run wide open for extended period of time should use single viscosity oils. If they are operated in very cold climates, low viscosity straight oils, such as SAE10 may be required.

thingy George,I knew it was one or the other? thingy
Sam Maybe they want to sell more replacement engines.
I'll have to dis-agree with Pete, here. I don't think comparing primitive multi-fuel motors and old straight-six Fords to modern motors is fair.
When was it exactly that "we" all decided "we" knew more about a motor and it's applications than the manufacturer?
Use the oil that the manufacturer recommends, is that so hard?
Listen, these "new" small engines have become very complicated. Hydraulic valve lifters, pushing overhead valves. Tolerances getting closer and closer. Anti-vibration weights etc, etc...
These new motors aren't cast-iron Kohlers! Lets just assume that the people who designed and built the motors know more about them than the "monday morning quarter-backs", shall we?


Bill Pete:
Lawn, Garden, and Industrial motors don't run at full throttle: they use governors to control engine speed by throttle opening. Most small engines are rated at 80-85% max loading as the max load by the manufacturer.
It has taken many years for small engine mfg.'s to embrace the multi-grade oils, especially the superior syntetics, but they have all come around to it.
As Mike mentions, some engines use hyd lifters, and that means high detergent multi-vis oils only. It maybe that the mfg's are recommending multi-vis oils so that nobody uses non-detergent oils, there still are some die-hards out there with Ford 9n's swearing by their 30 non-detergent oils! My $0.02.

Pete Well, my 302 cu in or 5.0 liter boat engine is not a "straight six old engine" but a modern electronic multiport fuel injected V8 engine (96 year model)which was used for many years in Ford trucks and SUVs, as well as in many Ford cars. This engine is essentially identical to the automobile version, except for marine grade accessories, such as starter and alternator. Explain then why do they recommend 30 SAE oil for this engine and 10W30 or 5W30 for the automobile version of the same engine.

When I said that industrial engine are operated at full throttle for extended periods of time, I wanted to point out that this is not the case with automobile engines, which are rum at high speed only intermittently.

John Interesting discussion... I am just changing oil on my 42" 21 HP G&S that runs great. It says 30WT but I have some 20-50 that I use in my older cars.
I live in Florida where cold is never an issue but heat really is. I don't use the tractor for anything other than grass and it only runs in Summer. Its about 3 years old.
What is your opinion of 20-50?

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