It's a 2wd '93. You are probably right , I just can't find it in my manual .


Edit: I think this is it. This picture is poor but the description fits
http://www.autozone.com/az/cds/en_us...rInfoPages.htm

 

soak part of a shop rag in PB blaster
use a block of wood to hold against the offending plug overnite

use a 1/2" or 3/4" long flex breaker bar with Mac or Snap On appropriate size adapter down to 3/8"
flex it hard and have helper use brass hammer to pound on flex bar 6" from head

most other 3/8" drive brand tools are too soft anymore, it's all the cheap steel and pot metal
even Sears is not the quality it once was.

 

The 3/8" socket in that plug? There's actually a special adapter to fit that hole that fits tighter than most ratchet extensions. You want a tight fit, or the square socket can strip and you'll have to resort to a drill (BTDT).

85W140 is not "thicker" than 80W90. The wider viscosity range is accomplished with an additive mix that provides equivalent viscosity "benefit" (spec testing) without actual viscosity change.

The "W" in the viscosity rating means it's rated for "Winter" use. Look it up yourself. I'm an amateur tribologist

IIRC, even though there is a bonded mag on the diff cover, the fill plug also contains a magnet. One ones I have rounded out and had to replace, I went to Ford to get a replacement with the magnet --- they are not stocked at most FLAPS.

Aeros 1990-on all have electric speedometer (whether digital dash or not) and the diff speed sensor. Also provides signal for CC and ABS. That's why you can't put a '89 and earlier diff in a '90-on Aero: no speedo, no CC, no ABS. Learned that one the hard way too.

HTH

 

i refer you to this article by an industry respected tribologist
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=729289#Post7292 89
"""
In mineral oil gear lubes, the Group I and II fluids dominate, since no high viscosity Group III has yet been produced. These fluids use bright stock and/or polybutlyene thickeners to thicken up oils for the higher viscosity oils such as the 80W140’s.
In synthetic gear oils, synthetic hydrocarbons such as polybutenes and PAO’s, along with esters dominate. Synthetic Gear Lubes shear little as compared to a mineral oil formulation with VII’s. Full synthetics loose little viscosity as the oil is squeezed, sheared and churned in the differential case. In most cases, synthetic gear fluids use no VII’s at all
"""
an 80w90 will have a viscosity of approx 15 cSt @ 100d C

a 80w140 will have a viscosity of approx 26 cSt @ 100d C

both will have a viscosity of approx 250 cSt @ 40d C

both of the indexed temps are industry standards used for viscosity comparison of different lubes

yes, both viscosities have about the same viscosity thickness at 40d C 104d F, i.e. parked in the driveway on a hot day,
but the 80w140 viscosity thickens faster as the temp rises
thus is "thicker" at operating temps.
most car diffs run in the 60d C range during summer
most heavy towing PU apps run in the 60d to 100d C range in summer

mineral oil differential lube has Viscosity Index modifiers that are long chain plastic like molecules which change shape with temperature change. these break down from wear and loads

synthetic lube PAO and or ester base stocks have the unique characteristic of dual viscosity at cold and hot temps, thin when cool thicker when hot. they require no or little Viscosity modifiers thus are less susceptible to load wear breakdown.

 

Woohooo! It's done!
I had to take a torch to it but the fill plug finally let go. It took about 2 1/2 bottles of Mobile 1 to refill it.
Thanks for the help and encouragement. On to the trans and power steering flush. My inline filters arrived

 

VanGo, making this mistake you are not the first, and belive, not the last one....