Synthetic vs. Multi-Purpose Fluids - NOT OIL QUESTION

[JeepLibertyKK]

I'v been dragging my feet getting all the necessary fluids for some maintenance work on my 2012 Jeep KK and 2003 Suburban, both four-wheel drives. Some of the fluids match up viscosity-wise, but not necessarily fluid type. For example, the older Suburban recommends 'synthetic' products for the front and rear axles but the Liberty states 'SAE 75W-90 Gear Lubricant' and 'SAE 80W-90 Multi-Purpose API GL-5 Gear Lubricant' as opposed to 'SAE 80W-90 Synthetic Axle Lubricant' for the Suburban.

I've always assumed that in these types of applications, synthetic is acceptable. But I don't want to assume and then do long-term damage to any Liberty components.

Your experience and recommendations would be appreciated!

Thank you.

 

[LibertyTC]

Always refer to the owners manual for your 2012 KK under specifications. Go with what is recommended.
As an example the rear diff may stipulate DINO 75W-90 but there may be clauses regarding if towing, where a thicker gear lube is required.
Also note what the change frequency is, on the KJ it is every 20K miles for rear diff.
I prefer the Lucas Dino gear lube wherever possible.

 

[tommudd]

ONLY reason they went to synthetic was to try and get that 1/10 more MPG, pure and simple
On gears in your diffs you want something that will " cling " to them so good old dino is the best period
I run 85-90/140 in all 3 of my Libertys all the time, of course they all pull trailers, 2 of them are used out in the fields etc on the farm so all get used
Plus I run them , wife works 5.5 hours away so nothing to jump in one and take off to see her for the weekend so I want something I can trust