FYI lesson learned on axle lube viscosity

[73azbronco]

So, my new to me jeep 3 years ago was modified with a lift and axle covers, doing so they needed to refill the axles and used Lucas single weight 140wt race lube. Fine, a little thick, but it's Lucas, sooooo. After the mod the jeep averaged 16.4mpg, uphill, downhill, around town, doing 75 down the road, AC on, windows open, didn't matter. It was what it was.

Never thought about the lube much until this week, 3 years and 25,000 miles later I need to do a 4x4 service to stay in warranty and change same axle lube. I ask them to use the stock 75-120 synthetic from Mopar.

Overnight I now get 18.7 MPG. 14% better mileage by changing viscosity. No reason to use that thick a viscosity unless I was racing or towing a 20,000# trailer. That thicker lube cost me an extra $600 in fuel.

 

[onebadd73]

Wow, great info..who would of thought..Thanks for sharing..

 

[Broncobowsher]

Daily driver company car at the time I could tell if the shop filled it with 10W30 or 5W30 as the gas mileage would change. The default fill was 10W30 unless I specified 5W30. It was only a small change in mileage but enough I noticed. At one point they were filling it and asking me what I they put in. After a couple tanks of gas I could accurately answer them.

So yes, oil viscosity does matter. Many new cars are now being filled with 0W20 oil. I have a motorcycle that I just filled with 0W10 oil that is working great. I would not recommend for stuff that isn't designed for it.

Current truck made no difference when switching from conventional to synthetic oils of the same weight.

Yes, I have played with this stuff. A lot over the years.

 

[blubuckaroo]

I always use the recommended product. The consequences are way too high for me.
I'm no oil engineer. That's way above my pay grade. Who am I to second guess their education?
If I add or change lube, I go to the manual to find out what's needed. Sometimes a unique and expensive oil is recommended by the manufacturer. There is usually a reason for that. Some manufacturers have custom designed gear oils to meet their particular need.

 

[Glass Pony]

I had a weird experience with a too heavy of oil which I believe was 140 weight also.
I had a Bronco II with a Lock Rite lunchbox locker and during extreme cold (10-20*F) within the first 1/4 mile of driving while cold you would ease it around a turn and end up with zero drive to the rear wheels like it was in neutral for a couple seconds, and then it would catch.
I think the cold heavy oil was slowing the couplers from engaging.

 

[Crush]

If you call ford and ask them what kind of oil they recommend for any ford product of any year and they will tell you 5w20.

 

[blubuckaroo]

If you call ford and ask them what kind of oil they recommend for any ford product of any year and they will tell you 5w20.

Seriously?
My manual breaks it down to climates.

 

[nvrstuk]

For sure...climate... -20F is a bit different than 110F