Should Differential Oil be synthetic? Is it worth the extra cost?

[Mike Shumack]

I changed the differential oil in my '05 Patriot Thunder.
The Owners Manual says to use "GL5" axle oil, and the manual provides a brand name "Pennzoil Gear Plus SUPER-EW 75W-90 Synthetic.

However Pennzoil doesn't make that line anymore. I bought Pennzoil GL5 80W-90 (non synthetic).  https://www.pennzoil.com/en_ca/products/other-oils-fluids-fuel/manual-transmission-fluids-axle-oils/axle-80w-90.html

So now I'm second guessing myself - and wondering if I should have gone with the synthetic (Pennzoil has a line they call "Pennzoil Platinum Axle 75W-90").

Do you think it will make a difference in the long run?

[Steve Huber]

Mike,
From Fleet Equip Mag:
"SAE 75W-90 maintains a more consistent thickness, or viscosity, across a wide temperature range. It's thicker when exposed to high heat and thinner under colder, wintry conditions than 80W-90. The use of 75W-90 gear oil is recognized by OEMs as a contributor to overall fuel economy."
Steve

[Eric Maclean Co-Admin]

Mike
Either oil will work in your differential how ever the most noticable difference between the two are as follows in any multigrade oil the first number represent the cold flow viscosity and the second number is the hot or maximum viscosity.
These gear oils hard formulated with higher levels of sulpher which is used to protect the gear surfaces from the high pressure contact to limit or eliminate spalding of the metal surfaces hence the name high pressure gear oil.
By trading off synthetic for non Sy thetic year oil you loose some of the advantages of the synthetic as follows
1) synthetic is thiner with a lower viscosity has a better flow rate when cold which gives it better lube ability and fuel mileage in colder weather.
2) synthetic gear oil formulations are much better at absorbing moisture a d keeping it in solution.

Most OEM now use synthetic oils throughout there products because of there superior lubrication properties allowing them to use lower viscosity oils which help produce better fuel economy.
As stated before both will work but personally I run synthetic in my diferential as well as my front hubs because of the moisture control which helps keep the wheel bearings from moisture and rust damage when sitting for long periods.

Hope this helps
Eric