80-90 versus 75-90; synthetic

[Whimsey]

My wife has a 2002 Explorer and her front diff requires 80W-90 fluid. I have a 2002 F-150 and my front diff requires 75W-90 fluid. I put Schaeffer's #267 80W-90 Supreme Gear Lube in both front diff's. The Schaeffer's #267 is a true synthetic blend. It works fine in my F-150, which "requires" dino 75W-90, even in zero degree and below days. Check with the Schaeffer's rep, Mark Smith, or check with MolaKule at Specialty Formulations for his offerings. Both offer quality products and both are site sponsors so you can find them on the home page.

Whimsey

 

[MolaKule]

quote:

---

My guess is that a synthetic base oil probably has a natural VI spread of 75-90 without the use of any VI improvers.

Certainly you can use 75W-90 in any application which calls for 80W-90.

John

---

John is correct. Synthetic gear lubes have such a large VI they don't usually require VII's.

Search in the Interesting Articles portion of Science and Technology of Lubricants and Oil additives such as:

http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=000226#000002

You should find at leat three white papers on this topic that show no VI used in most synthetic formulations.

 

[par]

Hi,

why is synthetic always 75-90 and never 80-90? I presume that the lower rating is a given for synthetic oil and offers more protection when cold therefore there is no real need for a 80-90 oil.

Is this correct?

ps. I realize that Amsoil offers a 80-90 but it seems that nobody else does.

 

[jthorner]

My guess is that a synthetic base oil probably has a natural VI spread of 75-90 without the use of any VI improvers.

Certainly you can use 75W-90 in any application which calls for 80W-90.

John

 

[Tremo]

My old Camaro has one of the BW "9-bolt" rear ends, and it calls for 80W-90 lube. I've been using RP and Redline 75W-90 synthetics in it, and it runs just fine. No chatter from the posi when I round a corner. No extra FM additives required.