Let's talk about gear oil weights ... wtf do they mean?

[dremu]

I've always wondered about mixed-weight oils, like 20-50. I mean, I know that 20W is like think soup, 50W oil is like thick soup, and 90W is like Jell-O... but what's with the mixed?

Also, I have a pair of gearboxes, calling for SAE20 in one and EP90 in the other.

I am going to GUESS that the (mixed) 85-90 I can get at the auto parts place is gonna be good enough for the second one (but what's EP?)

The first one, though, has me stumped. Do I just put in straight 30 and stop worrying? Some variety of mixed-weight, like 20-50 or 15-40 or 867-5309? I didn't find straight 20 at the parts house, but maybe it's only available via courier yak from the mountains of Guam?

-- A

 

[redbeast24740]

HEY I lived on GUAM for 4 years there are no mountains there. Only Beaches......

 

[Hogback Fabrication]

http://www.autoeducation.com/autoshop101/oil-change.htm

 

[pauly383]

Well ( learned on the net myself ) , the W means winter . SO a 10w40 oil is like 10 at low temps , and 40 at high temps .

Good little read , although I use Castrol Dino-Oil in my rides http://www.valvoline.com/carcare/articleviewer.asp?pg=ccr20040601ov

 

[dremu]

No mountains, and I am quite sure there are no yaks on Guam either, nor on Diego Garcia =))

Yaks aside, any thoughts on what oil I should use for these gearboxes?

-- A

 

[pauly383]

Well if they are getting rid of SAE30 in favor of 10w40 ( 20w50 for our rigs ) , perhaps 5w30 would work in place of SAE20

 

[Hogback Fabrication]

Also, I have a pair of gearboxes, calling for SAE20 in one and EP90 in the other.

SAE 20 oil is straight 20 weight. It will say SAE 20 on it.

The "EP" in EP 90 stands for extreme pressure. Most "EP" oils don't have EP anywhere on the container, they say they "hypoid" (a style of gear cutting) on them instead. Most 80W90 oils are meant for hypoid gears (just make sure it says that).

 

[dremu]

SAE 20 oil is straight 20 weight. It will say SAE 20 on it.

The "EP" in EP 90 stands for extreme pressure. Most "EP" oils don't have EP anywhere on the container, they say they "hypoid" (a style of gear cutting) on them instead. Most 80W90 oils are meant for hypoid gears (just make sure it says that).

Hokay, hypoid 80w90 or 85w90 is easy.

Where does one *get* SAE20 then?

The gearboxes in question are on my winch -- an older Ramsey, that shares its design with a whole family of industrial, i.e. tow truck, winches. Point being I wanna keep it happy, and if it wants 20 weight instead of 30 I'll do my best to feed it such. If it matters.

-- A

 

[4by4bygod]

Here's some info on gear oil designations, and the meaning of the EP designation.


SAE Designation of gear oils by viscosity The Society of Automotive Engineers (SAE) established a viscosity grading system for gear and Engine oils.

According to the SAE viscosity grading system all oils are divided into two classes: monograde and multigrade:

• Monograde gear oils

Monograde gear oils are designated by one number (70, 90, 140, 250, etc.). The number indicates a level of the oil viscosity at a particular temperature. The higher the grade number, the higher the oil viscosity.
Viscosity of gear oils designated with a number only without the letter “W” (SAE 80, SAE 90, SAE 140 etc.) was specified at the temperature 212°F (100°C). These gear oils are suitable for use at high ambient temperatures.
Viscosity of gear oils designated with a number followed by the letter “W” (SAE 70W, SAE 75W, SAE 80W etc.) was specified at the temperature 0°F (-18°C). The letter “W” means winter. These grades are used at low ambient temperatures.

• Multigrade gear oils

Viscosity of gear oils may be stabilized by polymeric additives (viscosity index improvers). Viscosity of such gear oils is specified at both high and low temperature. These oils are called multigrades and they are designated by two numbers and the letter “W” (SAE 75W-90, SAE 80W-90, SAE 85W-140 etc.). The first number of the designation specify the oil viscosity at cold temperature, the second number specifies the oil viscosity at high temperature.
For example: SAE 85W-140 oil has a low temperature viscosity similar to that of SAE 85W, but it has a high temperature viscosity similar to that of SAE 140.
Multigrade gear oils are used in a wide temperature range.



Extreme pressure (EP) additives

Extreme pressure (EP) additives prevent seizure conditions caused by direct metal-to-metal contact between the parts under high loads.
The mechanism of EP additives is similar to that of anti-wear additive: the additive substance form a coating on the part surface. This coating protects the part surface from a direct contact with other part, decreasing wear and scoring.
The following materials are used as extra pressure (EP) additives:

• Chlorinated paraffins;
• Sulphurized fats;
• Esters;
• Zinc dialkyldithiophosphate (ZDDP);
• Molybdenum disulfide (MoS2);

 

[RustBuket]

So here is my question then. If a 10W30 oil is said to behave like a 10 in cold conditions and a 30 at warm conditions. Does that just mean it doesn't thicken up so bad when it gets cold. Aka, only to a 10 weight oil level instead of a 30 at the same temp? I'm kinda confused as you can tell.

 

[Hogback Fabrication]

Where does one *get* SAE20 then?

When I replaced the gear oil in my 8274 (I forget if it spec'd SAE 30 or SAE 40 weight non-detergent oil) I found it at ACE hardware. I wouldn't be surprised if the auto parts stores had it too.

 

[user]

viscosity

A characteristic of any liquid is viscosity. A liquid is more viscous if it's thicker and pours more slowly, like honey; less if it's thin and runny, like water.

Oil viscosity index numbers are higher if the oil is more viscous, like honey, and lower if the oil is more runny. Viscosity is referred to as "weight", though that doesn't make much sense. Obviously, the index will change when oil gets warm (runnier) or cold (thicker). The index they print on the can is a standardized number so that oils can be compared - when any oil goes in an engine or gearbox, it will get runnier when it heats up, and thicker when it sets out all night in North Dakota in January.

So you want oil that's runny enough to go through all the little ports and channels it needs to in order ensure adequate lubrication, and thick enough that it'll maintain some body and hence oil pressure when it does so.

A multiweight oil is one that contains oil that is capable of acting runnier than a singleweight oil at lower temperatures, and thicker than a singleweight oil at higher temperatures. It's not necessarily a blend of different weights of oil, 'cause it's mostly oil that just has been refined to select for the proper range of viscosity.

I live in Northern Va., a humid subtropical climate; average temperature in the winter is about 45 degrees, I think, and in the summer, upper eighties. So I expect things to get hotter and not so cold as might be the case in, say, Michegan. So I get multigrade oils that have a high second number, and I don't worry too much about the first. I generally get motor oil that's a 10W40 for the truck and 10w50 for the four-cylinder cars which run hotter, since they have to rotate twice as fast to go the same distance. For the differentials, I use a mixture of 50/50 Lucas Oil Treatment and Valvoline 80w140 EP. (A differential doesn't have as many little tubes for the oil to go through, as long as it can get into all the bearings, it's ok.)