Okay, now I've drained the front and rear diff oils on my KQ. Now, on my 98 500 the manual says to use GL-5 hypoid oil so that's what I used in it and put in my KQ. I get to thinking I'd better double check (mind you I haven't driven this thing yet) and I see the front diff does take the GL-5 but the rear says to use a Mobilfluid 424 or equivalent.

So I think no big deal, I can drain it and I'll look up to see what's compatible.

I can't find what I need to know. I do believe that the Mobil fluid 424 is a GL-4 80W but I'm not sure. I can't confirm that. Mobil's website does give me that but it also says it's suitable for commercial transmissions requiring Type A (suffix A), Dextron and Type F fluids. That's what's really confusing.

Comparing specs and I see it seems to be a hydraulic oil which is much thinner than an 80W. So my question becomes, what are you guys using, or are all of you still on the factory oil?

I'm thinking the rear is going to take a 75W90 GL-4 but the heck if I know. I have read that you should not use a GL-5 oil in a GL-4 rated carrier. They are NOT compatible and only bad things happen.

So lets go a little deeper on this. The oil I've used on my 500, and what I'll finish filling the front diff with, is Cenex MP Gear Lube LINK HERE and they recommend, not only GL-5 but say "many applications for API Service GL-2, 3 & 4"

Comparing the properties of the two oils, the Cenex 80w90 is definately a higher viscosity @ 40*C and 100*C. Mobil fluid 424 LINK

If you look at Cenex Matron GL LINK you will notice their viscosity @40*C is 122, lower than the 141 of the MP Gear Lube but it is higher @100*C (16.6 vs 14.4) which the 424's are 55 @ 40*C and 9.3 @ 100*C

Now, to create more confusion, googling specs for the oils and anything I can think of to eliminate the confusion, only creates more. Which leads me to Amsoil's website and they have a Manual Transmission and Transaxle Gear Lube 75W90 GL-4 Oil LINK which is closer to Mobil 424's specs.

If I look up oils to match up close the the 424's Viscosities then I have seen a 5W30 oil almost match those #'s.

If you read the product description for 424, it's a multipurpose tractor lubricant designed for transmission and hyrdraulic fluids. Those oil's I'm familiar with using on the farm are very similar to a "lighter" oil.

So there now, does that clear anything up? If I could find any 424 oil locally, I'd just use it. There's literally tons of gear oil in my farming community but I'm just not sure what is equivalent to the specs required by Suzuki.

Josh, I'm sure you've at least changed your diff's once, what did you refill them with?

Sorry for the novel, but geez, this has been a little interesting to say the least and I'm not a fluids expert.