Yanmar Gear Oil

Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
The Jaguar XKE (as well as XK 150, 140, and 120. MGB also) called for 30 wt motor oil in the transmission.. When ya talk gear oils, the "weight" number is not the same weight number as motor oils.. For instance, viscosity is measured in Saybolt Seconds Universal (or centistokes). The specification for 30 wt motor oil is 58-70 SSU measured at 210 F (9.6-12.9 centistokes). The specification for 85 wt gear oil is 63 min SSU, measured at 210 F (11, minimum centistokes), in the same range as 30 wt engine oil. . Yes, the additive packages are different,with gear oils generally having additives to work successfully with hypoid gears (rear differentials with the drive gear offset below the axle centerline). Hypoid gears in particular have a lot more sliding at the tooth interface than do spur type gears as in say a Kanzaki .. The additives are strange in that they put a micro-coat of corrosion products on the tooth faces. The corrosion products are very hard and that is basically how they work. There are some very hard steels in the gears of a typical rear differential. They can stand (and are designed to) the aggressive action of the EP additives. Some/most extreme pressure additives in gear oils will attack bronze, which is what half of the cone clutch is made of in a Kanzaki. This is why Yanmar does not tell you to use gear oil. The gears, bearings and tooth face sizes in the Kanzaki are designed to work with an engine oil without the need for EP additives.
ATF, another animal entirely, has an approx vis of 7.8 centistokes, abut the same as 20 wt engine oil.. It is called for in transmissions that have disk (not cone) clutches as in an automobile automatic and many Kanzaki models and many Hurth models. .. Look at the plate on your transmission and use that oil.. If it uses a "retired" or obsolete engine oil rating, like CD, the newer ratings CE, CF, etc are generally superior to the older rating..
End Of Rant.. Google my facts to check if you'd like..
 
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DougM

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Jul 24, 2005
2,242
Beneteau 323 Manistee, MI
Page 16 of the manual that came with my 2GM20F states that the KM series gearbox (mechanical cone clutch) uses the same oil as the engine. The KBW series gearbox uses ATF-A. There is a note below that that simply says "Do not use ATF-A in KM series..."
To me its pretty clear that the significant difference results from the gearbox type.
(It might also be the difference in the ongoing threads about whether the gearbox should be locked in gear or allowed to freewheel in neutral while sailing.)
 
Sep 15, 2009
6,243
S2 9.2a Fairhope Al
(It might also be the difference in the ongoing threads about whether the gearbox should be locked in gear or allowed to freewheel in neutral while sailing.)
this related but also thread drift.......there is a directive from yanmar stating that the thing should be in neutral when sailing
 
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May 24, 2004
7,129
CC 30 South Florida
10W30 oil entails that when cold the viscosity of the should be 10 and at 100F it should be 30. I doubt the oil in the transmission reaches 100F so the multigrade might a little thin. If the manufacturer calls for 30W oil use a single grade oil. Although we may be splitting hairs here as these transmissions are hardy and have proven to run on all grades of oil.
 
Nov 6, 2006
9,885
Hunter 34 Mandeville Louisiana
To clear some misconceptions about multi-vis oil versus straight grade.. All engine oils decrease viscosity as they warm up. The slope of that line of decreasing vis with temperature is the "viscosity index". The multi-vis oil has a higher viscosity index than a straight grade oil so it decreases in vis as it warms, it just does not decrease as much as straight grade oil.. example.. 10 wt straight grade specified vis is around 2000 centistokes at 0 F.. 10W30 has that same vis at 0 F hence the 10 in its number. At 210F, the specification for 10 wt straight is a smidge over 7 centistokes. The 10W30 however at 210F has thinned (not as much as the straight 10 wt) to around 11 cenistokes, which puts it in the range of (but slightly less viscous than) 30 wt straight which would have thinned to about 12 centistokes.. The thing to know is that the multigrades satisfy the viscosity spec of the light oil at low temp and the spec of the heavier oil at high temp.. but that high temp vis is a lot less than the cold vis; both oils will have thinned a lot at the higher temperature.
(not trying to impress anyone, I am trying to clear up some misconceptions)
 
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May 24, 2004
7,129
CC 30 South Florida
I think we are going overboard on this. 30W motor oil has been the lubricant of choice for transmissions not requiring ATF for decades with good results. Why try to play Chemists?
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
+1 to Benny and Ralph. You can't go wrong with the manual UNLESS someone posts - not quotes- a factory bulletin stating otherwise.