SAE 90 vs SAE 80W-140

[metroplex]

I have a 2003 Ford E-250 w/ a Dana-60 rear end (3.73s, Traction-Lok limited slip).

The manual calls for dino SAE 90. I ran it for 500 miles before I changed to Redline 80W-140. THe Redline's cold temp viscosity is slightly higher than the dino SAE 90's, but the high temp viscosity for the Redline is thicker.

Would I be damaging anything by using this oil? My reasoning to use this was Ford specifies 75W-140 synthetic for its E-150 vans w/ the lighter duty Ford/Visteon 8.8" rear end. I don't understand why I would use straight 90 dino in a heavier (much heavier) duty E-250.

The difference between the E-150 and 250 is like night and day, whereas the difference between the 350 and 250 is very noticeable albeit not as much as the 150 and 250 gap.

I was looking for more protection at the sacrifice of drivetrain efficiency, should I switch to 75W-90 synthetic for the E-250?

 

[Greaser]

Owners manuals have been known for leaving out information or having incorrect information...people write the things and they make bo-bo's...personally I run synthetic 75W-140 in both my rear axles...Chrysler 8.25 with 3.55's and a Dana 44 with 3.73 gears...the manual says to use this weight when towing,snow plowing,off-roading etc.I just run it all year because I do these things intermitently and can't drop fluids everytime I tow...the Dana 60 is a fair sized axle and can beat the 75W-140 fluid around no problem..F250 is a good sized van...and yes it's been said here that the thicker fluid runs a tad hotter than the thinner fluid...but I believe film strength is bit more important than heat when pulling a heavy load..so I go with the 75W-140 synthetic...which probably will run cooler/protect longer than a mineral based 80W-90...but I could be mistaken...personally I think the 75W-90 is a little thin in a big truck...but I'm no expert...I use the 75W-90 in my front axles but not the rear axles...E mail Dana to get their opinion.

 

[TooSlick]

Metroplex,

Most over the road commercial trucks now run 75w-90 synthetics in the differentials, instead of the 85w-140 petroleum gear lubes that used to be common. I'd go with the Redline 75w-90 in this application ....

TS

 

[Greaser]

Isn't it true that the higher a gear ratio the hotter an axle will run?3.73 is not that high a ratio but it's getting up there...wouldn't a synthetic 75W-140 be a better choice?I just did a new Jeep with Dana 44's front and rear from the factory...they both are stuffed with 4.11's OEM..and the axle tags had "75W-140 synthetic" stamped on each tag..so thats what I put in (Pennzoil)...I go with a syn 75W-140 out back in a F250 van.