Oil

[EddieC]

Figured there's at least one gearhead in here that might know the answer. I recently purchased a new Craftsman 4 cycle weedwacker. The book tells me that after 10 hours I should do an oil change and use straight 30w oil. Is there any reason I can't or shouldn't use a 10W-30?

 

[N.V.M.]

are you sure it doesn't say SAE30W? a straight winter 30 oil flows good even in cooler temps. just a guess.

 

[EddieC]

are you sure it doesn't say SAE30W? a straight winter 30 oil flows good even in cooler temps. just a guess.

It does say SAE30W....isn't that the same as 30W, I thought the SAE was just the standard that oil is judeged or produced by?

 

[Topflite_D2]

Actually I think it is just SAE 30 because the 10w means winter.

 

[BrandonM7]

Long description of what the grades mean, taken from wiki so I don't have to type too much --
(short answer is below this, btw)

The Society of Automotive Engineers, usually abbreviated as SAE, has established a numerical code system for grading motor oils according to their kinematic viscosity. SAE viscosity gradings include the following: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. Some of the numbers can be suffixed with the letter W, designating their "winter" (not "weight") or cold-start viscosity, at lower temperature.
Viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperature. The longer it takes, the higher the viscosity, and thus higher SAE code.
Note that the SAE has a separate viscosity rating system for transmission oils which should not be confused with engine oil viscosity. The higher numbers of a transmission oil (eg 75W-140) do not necessarily mean that it has higher viscosity than an engine oil.

[edit] Single-grade

For single-grade oils, the kinematic viscosity is measured at a reference temperature of 100 °C (212 °F) in units of mm²/s or the equivalent older non-SI units, centistokes (abbreviated cSt). Based on the range of viscosity the oil falls in at that temperature, the oil is graded as SAE number 0, 5, 10, 20, 30, 40, 50, or 60. The higher the viscosity, the higher the SAE grade number is. These numbers are often referred to as the 'weight of a motor oil'. The reference temperature is meant to approximate the operating temperature to which motor oil is exposed in an engine.
The viscosity of single-grade oil derived from petroleum unimproved with additives changes considerably with temperature. As the temperature increases, the viscosity of the oil decreases logarithmically in a relatively predictable manner. On single-grade oils, viscosity testing can be done at cold, winter (W) temperature (as well as checking minimum viscosity at 100 °C/212 °F) to grade an oil as SAE number 0W, 5W, 10W, 15W, 20W, or 25W. A single-grade oil graded at the hot temperature is expected to test into the corresponding grade at the winter temperature; i.e. a 10-grade oil should correspond to a 10W oil. For some applications, such as when the temperature ranges in use are not very wide, single-grade motor oil is satisfactory; for example, lawn mower engines, and vintage or classic cars.

[edit] Multi-grade

The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold ambient temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. A specific oil will have high viscosity when cold and a low viscosity at the engine's operating temperature. The difference in viscosities for any single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers, or VIIs are added to the oil. These additives make the oil a multi-grade motor oil. The idea is to cause the multi-grade oil to have the viscosity of the base number when cold and the viscosity of second number when hot. This enables one type of oil to be generally used all year, and when multi-grades were initially developed, they were frequently described as all-season oil. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the base oil.
The SAE designation for multi-grade oils includes two grade numbers; for example, 10W-30 designates a common multi-grade oil. Historically, the first number associated with the W (again 'W' is for Winter, not Weight) is not rated at any single temperature. The "10W" means that this oil can be pumped by your engine as well as a single-grade SAE 10 oil can be pumped. "5W" can be pumped at a lower temperature than "10W" and "0W" can be pumped at a lower temperature than "5W". The second number, 30, means that the viscosity of this multi-grade oil at 100 °C (212 °F) operating temperature corresponds to the viscosity of a single-grade 30 oil at same temperature. The governing SAE standard is called SAE J300. This "classic" method of defining the "W" rating has since been replaced with a more technical test where a "cold crank simulator" is used at increasingly lowered temperatures. A 0W oil is tested at −35 °C (−31 °F), a 5W at −30 °C (−22 °F) and a 10W is tested at −25 °C (−13 °F). The real-world ability of an oil to crank in the cold is diminished soon after it is put into service. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle (although some modern European cars now have no viscosity requirement), but can vary from country to country when climatic or fuel efficiency constraints come into play.

Use 10W-30 if you want to, it'll be fine. But it's not like straight 30 is hard to find -- every parts store has it, probably because just about every piece of lawn and garden equipment specs it. The bigger difference between the two is likely all the crap that's in it - 10W-30 probably has all kinds of energy saving additives in it to make the cars and greenies happy, whereas the straight 30 likely has lots of detergents in it because it's typically used in nasty old tractors and such. But I'd be willing to bet that more than a few brands put the exact same stuff in both bottles and just use a different label.

 

[EddieC]

Thanks Brandon, good info that I can use.