75w-90 in place of 75w-140...

[Toy4x4runner]

What do you guys think about this: I have a 2007 F250 and the rear axle is a Sterling 10.5"? Full Floater with 3.73 LSD. The axle tag and my owners manual is calling for 75w-140 FULL SYNTHETIC oil plus LSD friction modifier. First off the truck is stock, and I use it as a daily driver. I don't really tow or haul anything with it with much weight. I started thinking that if I put some 75-90 in place of the 75-140 I'd probly save some fuel? Time to change the gear lube in the next few weeks. To go with the thinner gear lube I would put a Finned Aluminum diff cover (capacity will not change) on it to help keep temps down. I can understand why they'd spec 140wt though... 3/4 ton HD truck ment to tow. That's cool and all but i'm not using the truck no wheres near those limits.

 

[Audi Junkie]

OK, well you can mix them too.

 

[Toy4x4runner]

Oh you can!? Did not know that.... so a 50/50 maybe. I'm always looking to gain some MPG's somewhere. Diesel is still expensive; relative to gas.

 

[Jim Allen]

With a synthetic 75W140, vs a synthetic 75W90 I doubt you'd see much more than a fractional difference in fuel economy. Probably not observable, in my opinion, using conventional MPG checking methods. That said, if you don't tow, use the finned cover a robust 75W90 would be fine in my opinion, as long as "Funny Farm" isn't in a very hot climate.

 

[Fordiesel69]

You can absolutly go to a thinner fluid if you are not towing. However I have heard bad things about mobil 1 gear lube. I am not sure what is bad but people say their wheel bearings don't last. Try amsoil or redline. I don;t beleive valvoline makes full, but you could look.

If you go thinner, the worst damage you will do is wear out your LSD clutchs faster. Not very expensive anyways. Use ford friction modifier though.

I took the 140wt out of my crown vic because thats what they fill the police packages with at the factory. I did do lots of other stuff to the car at the same time, but my mileage went from 21 to 23. Again too many things changed for me to rule that out.

 

[Toy4x4runner]

I'm down here in South Florida. Valvoline does make a full syn gear lube in either 75-90 or 75-140. I've used both Mobil 1 and Semi-syn valvoline. Valvoline has never let me down. Especially off-roading. Either doing Mobil 1 or Valvoline... no botique oils.

Little things add up in MPG land. After I get the Gear lube straightened out I'm going to be switching to 10w-30 Delvac (if I can find it!) or 5w-40 Rotella/Mobil 1. I do a lot of city driving and short trips.

 

[Fordiesel69]

Originally Posted By: Toy4x4runner
I'm down here in South Florida. Valvoline does make a full syn gear lube in either 75-90 or 75-140. I've used both Mobil 1 and Semi-syn valvoline. Valvoline has never let me down. Especially off-roading. Either doing Mobil 1 or Valvoline... no botique oils.

Little things add up in MPG land. After I get the Gear lube straightened out I'm going to be switching to 10w-30 Delvac (if I can find it!) or 5w-40 Rotella/Mobil 1. I do a lot of city driving and short trips.


Get an EGR delete kit. That will help the MPG's. Run 5w-40 syn for 5k-7.5k. I heard good gain for people who have a tuner. My buddy picked up 3 MPG just by a flash alone, and more power. Just don;t use that power and you will have gains. Plus the 6.0L's don;t like more boost unless you stud the heads.

 

[FiremarshalRob]

I don't see how the MPG gains would be measurable by switching to a thinner gear lube. I tow VERY rarely with my 06 F250, but I feel comfortable putting in what the mfg recommends. It will protect your rear differential better, esp if you find yourself towing a heavy load one day.

I opted for Valvoline Synpower (fully synthetic) 75w-140.

 

[Ken2]

Stick with the recommended viscosity. You'll never save enough fuel to pay for a possible differential rebuild.

Every GL-5 differential gear oil I've seen already has all the limited slip friction modifiers needed. (By the way, the LSD additive is only needed for clutch-type LS.) If the label says that the gear oil is good for limited slip differentials, use just that. When you change the gear oil, drive slow, tight figure-eights to work the new oil into the clutches. If you don't get any chatter, you're good. If there is some chatter, add 1/4 tube of add at a time, work it in, and see how things go. More is not better.

 

[Toy4x4runner]

10-4 guys. I'll just go with 75-140. Just not sure if I should do Mobil 1 or Valvoline Syn. ?? what do you guys think?

 

[NHHEMI]

I would go with the Valvoline of the two listed. One of the "boutique" oils as you put it would be a better choice however and I doubt you pay much if any more $$$ for it.

Royal Purple , Amsoil, or Red Line would be a better product but use what makes you happy. I also vote for staying with the 75W-140 - glad to see you decided to stay with the mfg reccomendation.

 

[Boomer]

I have used Mobil 1 gear lube for MANY years and have never had a problem. Diff cases were always very clean when I took the cover off of my Chevy truck to drain the fluid. Never any bearing problems as someone suggested above. Also, I would follow the manufacturer's rec and use the 75W-140 in your diff.

 

[dnewton3]

If you want to put any stock in a somewhat biased, but decently written report with adequate analysis, there is a good paper on the Amsoil pages regarding GL-5 diff lubricants.

Overall the Amsoil Severe Gear came out on top. The runner up, and the only one even close, was Mobil 1 synthetic. All the others were farther behind by a decent amount. Sure, it was done by Amsoil, but the report was reasonably done, and at some point you have to put your faith in some people's work; it was notarized for authenticity.

Synopsis? Amsoil did the best, but Mobil came in second, and it's a fair bit cheaper. Kind of a "best buy" of GL-5's.

If you don't like the message, don't shoot me. Read the report for youself and then nitpick with the author. I did.

 

[Toy4x4runner]

I was looking at the spec sheets on the Valv & M1. M1 seems to have a much higher Flash point than Valv, and M1 has a higher VI. and lower Pour point.

 

[FiremarshalRob]

I think you'll be satisfied with any good name brand. Amsoil, M1, Valvoline. Its hard for me to believe you'd notice a difference while driving, pulling, towing, hauling, etc.

I've got too many fellow firefighters that pull all day with their heavy duty diesels and I always ask them how many miles are on their rigs. When they tell me the mileage I then ask them how many times they have serviced their rear diff. They look at me puzzled and say "Hunh".

I opt for a lot of Valvoline products. USA made in Ashland over in Kentucky I believe.

 

[UncleRunkle]

I'll probably get flamed for this, but if you wanted good MPG in and around town and aren't towing/hauling "anything of much weight" why the F-250 diesel beast? Why not a mid size PU? or an regular F-150?

 

[D-Roc]

Originally Posted By: UncleRunkle
I'll probably get flamed for this, but if you wanted good MPG in and around town and aren't towing/hauling "anything of much weight" why the F-250 diesel beast? Why not a mid size PU? or an regular F-150?


I believe the OP's question was related to the weight of gear oil in their diff and not his choice of vehicle...

 

[Toy4x4runner]

when I bought my truck diesel fuel was much cheaper than 87 octane Gas. I got a great deal on my truck being it was one of the left over and the new model was already flooding the lot. plus... I do like big axles. That was a huge turn off for me on the F150... IFS and Semi-Floater rear. I like to get out wheeling/camping every now and then. But even the F150's call for 75/140 and the old (up to '08) F150's get pretty [censored] mileage... SO the reality is the 2009 FX4 F150 is the truck for now that it has 21 MPG's, gas is cheaper than diesel, FX4 models have E-Lockers and now they have 6spd transmissions. Day late and a dollar short.... financially stuck with my truck now.

 

[Jim Allen]

FYI, there is an F-150 with an 8200 GVW ('04-08).Thre is a similar '09 package. I have an '05. It mounts a Sterling/Visteon 10.25 rear axle with 4.10 gears standard, rated for a 5300# GAW (gross axle weight) and 8300 lbs-ft of intermittent torque (1600 lbs-ft continuous). The axle is a semi-float but has 1.5-inch, SAE 1050 high-carbon steel, 35-spline shafts and huge bearings. With a heavier chassis and springs than a regular F-150, it's rated for a 2,670# payload (3000+ for 4x2) and a 9500# trailer rating (9900 4x2). Engine, trans and t-case are the same as the other 5.4L F-150s, but it comes standard with a huge tranny cooler, power steering cooler, uprated cooling, the trailer tow package, 35 gallon fuel tank and a few other goodies. It replaces an older 8600# GVW F-250 diesel very ably and gets much better mileage. With engine tweakage and careful driving, I can reach 20 mpg on level roads at 60 mph. My overall combined mpg is around 15.5. The only downside to this "Payload Option" F-150 (for some), is that the highest trim level is XLT and the maximum cab is a supercab. Mine's a longbed regular cab XL, which is what I wanted. You see lots of these F-150HDs (my appelation) in government and commercial service. Kinda hard to find, actually.

I'm a Luddite, too, in my preference for solid front axles but since this truck is not a 'wheeling truck and 33s are the biggest tire it will ever see, I can live with IFS. Nice driving and still about a thousand pounds lighter than an F-250 gasser.

 

[Toy4x4runner]

Wow. did not now that.. I thought they only offered the 8.8", and the 9.75". Learn something new everyday. 15.5mpg avg is not great. Around tampa I can average 16-17. But gas is $1.10 cheaper per gallon, so you still come out way ahead. The new 6spd trans, new E-locker and better mileage are very appealing in the new 2009 trucks. But financially I can't get into one w/out taking a bath on my 1.5yr old F250. so even if I save X amount of dollars on fuel per month... still have to front about $6k. $6k in the bank pays for a lot of diesel price difference. I'm just gonna have to watch the market on this over the next few yrs and when it makes more financial sense make the switch. This F250 is a money pit:

1- Head studs that should be done BEFORE they need it: $500 studs, $100 warranty deductable, $250 to grease the wheels.Not to mention 2 weeks w/out a truck. And while you're there it's not a bad idea to delete the EGR system: $500

2- Diesel fuel: Now $1.10 more expensive per gallon than gas. When gas was $4, diesel was $5. This is a losing battle here.

3- Theft deterantcy: Had the truck broke into 2x in less than 6 months. This truck is easy to get into and a eye catcher. The door lock needs swapped to a non-key unit: $50. Jimi jammers: $75. Alarm syst: $600.

4- No Locker option. FX4 is a LSD. so if you want a locker.. $500-$1,500 depending on unit/labor.


Ok, my rant is done.