I notice that for Honda gear case and differential oils the owners manual recommends "hypoid" gear oil. Not sure why they just don't go with the more modern GL5 designation????

And, the owner's manual says to use 80 weight, but Honda's own shaft drive oil is 80W90.

http://www.answers.com/topic/gear-oil

 

Actually, the GL ratings dont necessarily mean compatibility with hypoid type gears. Hypoid gear sets, like the rear differentials on trucks and some cars, require an "extreme pressure" additive, usually sulfur (that's why your hypoid gear oils smell like crap) But the GL ratings are separate rating, it's like saying any 10w30 SM oil is the same as 10w30 SG oil, but the SM is a newer designation, and simply repaces the older designation. Same thing with the GL ratings, GL-5 is the newest and replaces GL-4 and lower (usually). Chances are, if it has sulfur in it, it's for hypoid gears, and if you bought it lately, it's probably GL-5.

But, nowdays the only place gear oils are used are usually hypoid type gear sets, so you'll probably never find a GL-5 gear oils that ISNT hypoid compatible, so you are right in saying that honda should just say GL-5. As for the Weight, 75w90 or 80w90 are good to use. I dont know about 75w140, might be too thick in cold weather. I have Mobil 1 synthetic 80w90 in mine right now, still gold like brand new after 500 miles.

Another good example is the current Amsoil 10w40 motorcycle oil. It passes a GL-1 rating even though it's considered a motor oil, but the film strength is good enough for use in anything that requires a GL-1 rating, but it says specifically on the bottle not to be used in hypoid gear sets, most likely because there's no sulfur in it for extreme pressure protection. I think Amsoil cosidered the fact that it will be used in many engines that share oil with the transmission, where the oil will be used to lubricate GEARS too, hence the GL-1 compatibility, remember the gears in your transmission are NOT hypoid gears, so no sulfur is needed.

And I would recommend the Amsoil 10w40 Motorcycle oil to anybody looking for a good oil. Costs about the same as the Honda oil too, at least where I'm at. It is Jaso MA certified and says right on the bottle safe for wet clutches.

 

I have been running Mobil 1 in my diffs for about a year. I would however like to switch to an ester synthetic, seeing that the esters are charged molecules that stick to metal like a magnet, where the PAO of Mobil 1 is neutral and doesn't stick to anything. So, I was thinking about Maxima's synthetic which is GL5, but they don't call it "hypoid".

My understanding from the link I posted above was that all GL5 oils are "extreme pressure", and therefore the same as "hypoid" (?????). If so, it would seem that dumping the hypoid word would save a lot of confusion.

 

I went back to Maxima's web site, and in the fine print they do say the synthetic is for use in hypoids, so I answered my own question!