Have a 2011 Grizz 700 and for the diff oil the manual calls for SAE 80 API GL-4 hypoid gear oil. I'll be using Mobil 1 synthetic but as it comes in two different weights I'm not sure which one to get....either the 75W-90 or the 75W-140.

The 75W-90 is listed as GL-5 and is recommended for use in 'high-performance vehicles like SUVs, vans and light duty trucks.' The 75W-140 weight is also GL-5 and is recommended for 'high-performance vehicles including sport utility vehicles, vans and light-duty trucks.'

 

That's a good question.
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Save your money, just get a bottle of cheap Hypoid gear oil 80 or maybe 80/90W. I use Valvoline in my Arctic Cats. Works good, comes out clean every time, no water gets by the seals. Synthetic is for high heat, high load applications, thats why I use synthetic oil in the motors= Rotella T6. ATV differentials should never get hot enough to warrant synthetic. Like dumping expensive single malt Scotch into the punch bowl.

 

Thanks hydrex. Being told elsewhere that syn oil in a little bit older machine's diffs can lead to both leaky seals and water contam. So since I don't ride that much or that hard I'll prob just stick with some of the cheaper oils.

 

Synthetic oils and lubes are thinner in nature than dino oils so they can sneak past worn seals much easier. They also have more detergents so they clean the gunk better leading to worn seals also. On my new machine I do use syn 75w-140 in my diffs even though the factory calls for straight 80-90 wt. Being new I don't have to worry about seal issues. However in every test ever performed the syn lubes are more slippery and perform better than the best dino oil ever made so their is some advantage. If I were changing my diff lubes on a frequent schedule then I probably wouldn't spend the money but changing every couple years is no big deal. I also use syn motor oil in all my toys as the oil does not get changed that often due to low miles so the cost is nil and the protection is big. In my cars I do use dino oil as it gets changed every 3000 miles. My 2000 Blazer has 150,000 and oil is still fairly clean after 3000 miles.

 

Thanks Kymco. Have you heard about this water contam issue w/ synthetics? Would that be related to the leaky seals issue?

Also, do all GL-5 oils meet and exceed the requirements of the GL-4s or is it possible that in some applications it wouldn't be appropriate to substitute a GL-5 for a GL-4?