Do what your owner's manual says. If your LB has a Tecumseh engine, the manual specifically states that if you use a multigrade oil (10w30), you'll suffer higher oil consumption. No reason for you to use a multigrade unless you're starting the mower at temps under 40f

Find the 30W oil in the convenient 20 ounce bottles at Wal Mart, Home Depot, Lowes, etc.. This is the correct amount for the initial fill or an oil change. It may be marked 'Briggs & Stratton' or whatever.

Well, i suppose the folks who designed and built the machine, decided to have the buyer do a dance, and insist he buys 30W oil to use in his machine! Their recommendation couldn't have had anything to do with longevity, or better performance, naw, nothing like that--why, they are probably setting back in their corporate chairs, guffawing about the sight of some buyer running all over town, trying to find 30W oil!
Come on, fool! Buy the 30W--costs the same as 10w-30! And, if you have any type of older mower, or tractor, and the manual (Whats that?) says 30W oil in summer, I'd think the engineers probably thought that one up--probably in the hope that it just might make the engine last much longer!
Rants by Rusty Jones

Or maybe because they were making engines before they were making 10W-30?

A 20 ounce bottle MIGHT be the proper amount to refill. Sometimes you don't always get ALL the oil drained out or your engine may only take 18 oz. The SMART thing is refill TO the full mark.
Buy a qt. and you have some in reserve in case you have to top it off later. Any generic auto parts store will have 30 weight.
Personally, if I HAD 10W-30 on hand, I wouldn't have any qualms about using it.

Mary, to be more specific regarding your question.

Oil weight(wt) is the viscosity or ability to flow. The higher the number the thicker the oil is. As oil gets hotter it thins out. Thin oil gets to parts quicker on a cold engine so in cold operating conditions thin oil is preferred.

Straight 30wt is just that. 10w30 is 10 wt oil with additives that make the oil behave like 30wt oil when hot. Once hot, 30 wt oil gets pretty thin but straight 10wt would become like water. Your ambient temps are what needs to be considered whether to use 10w30 or straight 30. Since most mowers are operated in warm weather most of us old timers prefer using straight 30wt.

Thing is most of us old timers will also let our engines warm up a couple of minutes at idle. Many mowers these days no longer have throttle control, only a fixed high speed throttle so many manufactures now advise using 10w30 to give proper protection when the engine is cold and revving.

Really is no problem using the 10w30 all the time if it makes you feel better. Just make sure to do oil changes according to your owners manual. Multi grade oils under extreme conditions and getting long in the tooth can lose the ability of those additives to change oil into the heavier wt when hot, leaving you with nothing more then the base 10wt oil. If changed when its suppose to be done you shouldn't have that problem.

I have a friend that has been running a small engine repair shop for 15 years, and i just started my own shop, he always uses 30w. Go with the manual, it there for a reason.

Even more info on oil, regarding multigrade oils....

Take a 10W30 oil that starts its life as a 10, and has polymers added to it to make it behave like a 30 weight oil when hot. (as the poster above mentioned).

Over time, the multi-weight oil will shear on a molecular level, thinning out. Your 30 weight oil is no longer a 30 weight oil. Over time, the oil will oxidize and load up with combustion by products and thicken back up to a 30 weight. The oil may never get a chance to thicken back up, because you are dumping it out at 25 hour intervals.

The above is fact.

The following is opinion:
I honestly think that the older engineering behind the L-Head engine makes that engine dependent on running a thicker oil. A straight 30 weight oil will give constant protection from the time it's fresh to the time it's replaced.

'A 20 ounce bottle MIGHT be the proper amount to refill. Sometimes you don't always get ALL the oil drained out or your engine may only take 18 oz. The SMART thing is refill TO the full mark'

Totally unnecessary. When you dump the hot oil out of the mower by tilting it up on the right-side wheels, there won't be enough oil left in it fill a teaspoon. Even if there were a whole ounce left in it, you wouldn't even see it on the dipstick. Sure, check the dipstick any time you do an oil change on anything, but with the new clean oil you won't even be able to see it on the dipstick. Bottom line, the stated crankcase capacity is 20 oz. The oil comes in 20 oz bottles. You dump the old out and put the new in - it does not require micro-measuring or scientific accuracy. There's no need to try to make this simple task more complicated, thus persuading many to not even try it.

There are some exceptions to stated crankcase capacity. I just "summerized" a snow king engine on a snowblower I picked up last weekend.

The engine manual stated that the crankcase capacity was x. I filled it with x amount of oil and the dipstick read nowhere near full. I made sure that everything was level, double checked the manual and triple checked how much I poured in. Everything was according to spec but I still had nowhere near full showing. WTF?!?!

So I added and checked and added and checked until the stick was showing full. The engine took an extra couple of ounces to show full.

The solution to the mystery? The engine has a drain pipe that extends out to just over the rear of the blower frame to make draining easy.

I know that a snowblower is not a lawn mower, but it's always wise to never assume and to double check.

Otterhead wrote:
"Take a 10W30 oil that starts its life as a 10, and has polymers added to it to make it behave like a 30 weight oil when hot. (as the poster above mentioned).

Over time, the multi-weight oil will shear on a molecular level, thinning out. Your 30 weight oil is no longer a 30 weight oil. Over time, the oil will oxidize and load up with combustion by products and thicken back up to a 30 weight. The oil may never get a chance to thicken back up, because you are dumping it out at 25 hour intervals."
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This is absolutely true when talking about conventionally-refined "dino" oils. The viscosity modifiers that make a base stock a multi-weight have much larger molecules that don't like high temps or severe shearing loads. And in air-cooled motors with less even cooling than liquid-cooled motors, that's what you tend to get - hots spots with uneven expansion and clearances where shearing becomes an issue. The single-weights withstand this abuse better than the multi-viscosity dino oils.

The advent of true synthetic oils has really changed this, however. True synthetic base stocks have the multi-viscosity properties from the beginning, and they have fantastic high-temp-high-shear properties. In fact, all oils have spec sheets with an HTHS viscosity rating, where higher is better. The best numbers are achieved by wide-variance true Group IV or Group V synthetics, such as Mobil 1 0w40 or Schaeffer 9000 5w40. Back in the land of reality, I think most people don't put $5/qt oil in their mowers, and therefore are using good old dino oil. For them, the straight weight still makes plenty of sense. If someone is willing to step up, then a 10w30 or even a 5w40 Group IV synthetic will provide better protection over a much wider range of temps. The bottom line is that it's really impossible to get the full story on motor oil just by reading the nominal viscosity.