250w Gear Lube

[Mr Carts]

My AMC 20 has a bit of a whine.

Using 140wt gear lube as per factory tow package recommendation.

The KOH guys are running 250wt.


Anyone running 250wt in their FSJ

[joe]

250W??? Yikes I hope it's at least a syn gear lube. Dino 250 is gonna be some serious thick juice. ( May quiet down your differential a bit but not guaranteeing it'll get into the bearings. If your diff is whining/howling at speed and you lift your foot off the gas and it quiets down...your ring gear is seriously worn and you're in for a new R&P set.

[mwood65]

Where do you get that and what is it for normally?


I have never heard of 250 wt gear lube. Must be like molasses in January!!

[Mr Carts]

I got it from Summit Racing:

https://www.summitracing.com/parts/MAO-49-439128

The KOH guys are using it in the Ultra 4 4400 4x4 Buggys.

In my research I found that 250wt was used in diffs of Ferraris built in the 60's, and many of the older US cars including Packards , Fords and Studebakers.

I live in the middle of the Mojave desert where in the summer it is well over 115.

I have not put it in yet but once I do I will let you know the results.

[Mikel]

I think you are better off finding what is causing the problem and fixing it. If you have a bad pinion bearing, you are going to end up with a lot more damage if you ignore it.

[FSJunkie]

That's odd because my 1972 Jeep service manual specifies SAE 80 grade gear oil for the Dana 20.

SAE 250 and SAE 250W are very different viscosities at the same temperature. SAE 250 is the same viscosity at 212 degrees Fahrenheit as SAE 250W is at 0 degrees Fahrenheit.

That's the difference the W after the number means. It means that number which represents the viscosity of the oil was measured at a different temperature, 0 degrees instead of 212 degrees. That is why back in the day they used to have SAE 20W-20 oil. It was a viscosity of 20 at 0 degrees and stayed a viscosity of 20 all the way up to 212 degrees.

The Dana 20 should make absolutely no noise in 2-hi but will whine slightly in 4-hi. It whiles significantly in 4-lo. That is absolutely normal.

[Cecil14]

OP is referring to the AMC 20 rear diff, not the dana 20 tcase. In either case, 250w oil of any variety is too high for my blood. Your bearings were not designed for that, and are likely to starve.


aa

[Mr Carts]

Currie sells 250wt for use in their axles:
In all racing and extreme duty applications we recommend racing and extreme duty oil! We offer a 250 weight racing oil for these applications in a 4 liter jug.

https://www.currieenterprises.com/currie-250-wt-racing-gear-oil

So I do not think there should be any bearing lubrication problems.

Just waiting on FED EX to drop it off.

I live in the middle of the Mojave Desert the average coldest temp is 41 but the record is 10.

On the other hand summer usally is just a few degress cooler than Death Valley, we have 120+ days.

[nograin]

That's a huge jump in viscosity.
J306 uses 100*C (212*F) to define the grade.
See here: https://www.widman.biz/English/Tables/J306.html
Of course diffs don't run that hot.

Mr Widman notes the typical working range is 20 - 50*C, (68 - 120*F)
He has graphed the viscosity of several average typical gear oils.

This first one is in spanish by accident but even I can still read it.

https://www.widman.biz/English/Tables/Graph-diferentials.html

Detailed here in English for 20 to 40 degrees C

https://www.widman.biz/English/Tables/Graph-diferentials_files/ns_Entre_20_y_40.html?TB_iframe=true

And here for temperatures around 50*C (120*F) and higher

https://www.widman.biz/English/Tables/Graph-diferentials_files/ns_Entre_40_y_80.html?TB_iframe=true

Example of how to read these charts:
Lets assume high load in the diff brings the oil to 120 F (50 C).
Follow the temperature line up 'til meets the 250 curve.
The 250 Gear Oil has a viscosity of 500 centiStokes at 120 F.

Lets do the same for the recommended trailer towing 80W-140 gear oil. Lets just approximate between the two 140's he shows.
A 80W-140 gear oil has a viscosity around 225 centistokes at the same 120 F (50 C).

In comparison, the normal use 75W-90 has a viscosity of 225 centistokes only down at 68*F (20*C).
Clearly its working range often goes higher because even road temperatures alone go over 100*F.
So we can estimate the acceptable working Viscosity range is 225 to 60 Centistokes.

So the real question with the heavier than recommended gear oil is how much hotter is the diff getting. (We know from the graph the 250 gear oil will be around 225 centistoke around 65*C)
The second question is whether the driver(s) will be gentle with it until it gets warmed up.

My .02

[FSJunkie]

Oh, my bad. AMC 20 axle, not Dana 20 transfer case.

Shows I'm used to the older FSJ's.

Still. 85W-90 is perfect. I use 85W-140 if it'll see a lot of towing. If it whines it needs rebuilt. No oil will fix that.

[Mr Carts]

I live 4 miles off the pavement so it takes about a 20 minute drive on the dirt road to get to the County road.

Fed Ex dropped it off, Opened it up and it is not as thick as I thought it would be.

It looks like flows better than the 140 I am using now.


Going to put it in and see.


My Diff whine has been the same for the last 5 years which is about 20k miles of driving.


So this is not a sudden noise that just started.

I do not have any carpet on the rear area just bed liner so I do get more noise than a FSJ with carpet.

[rocklaurence]

Where do you get that and what is it for normally?


I have never heard of 250 wt gear lube. Must be like molasses in January!!

Its called Grease in Florida

[Mr Carts]

I changed the straight 140wt out of the diff. no metal in the gear lube nice and clean.

The 250wt went in it took 3 quarts.

Did a round trip to town and back much quieter.