MPG increase w/synthetic?

[Dookie]

Hey everyone. I'm trying to figure out if I will get a MPG increase if I switch my rear diff. fluid to synthetic? The weight would be the same, which is 80W-90 in this case. This is for my '05 Nissan Armada. I was thinking about going to Amsoil 80W-90.

Thanks!

 

[M3 Mitch]

In general you do get a small MPG increase, it's more noticable in cold weather.

FWIW when I changed out the factory fill trans and diff fluid on my BMW 325i, 1989 model, to Redline MTL and 75-90 gear oil, I didn't see more than a few tenths of a MPG improvement.

But in the Las Vegas heat, the synthetic would provide a better margin of protection I think.

 

[TheFuror]

I am not sure you will get noticeably improved mileage. You will get better longevity with synthetic, IMHO.

I would go with 75w-90, as opposed to a synthetic 80-90. Many people, BTW, have said great things about AMSOIL's Severe Gear 75w-90.

Another excellent choice would be Specialty Formulation's HDS-5 75w-90 gear oil.

Best of luck.

Bob W.

 

[TR3-2001SE]

I think it will give you better milage. I use Redline synthetic in my transmission and rear end of my Miata. I seem to get better milage that most people. I average 30mpg on my around town and commute to work. I can average 33-34 on the highway on trips at 65-70mph which seems to be above average milage for my car.

 

[Brian Miller_dup1]

If you MPG does go up, it will only be slight.

I have run the factory dino 80w-90, M1 75w-90, SF 75w-90, SF 75w-140, Redline 75w-90 in my diff, and getting ready to put in Exxon 85w-140 with some LC (heard back from Odis). I havn't seen any difference in mileage at all. I'm needing the heavier weight due to the locker that I installed

I would have liked to have a temp gauge in the diff to see what the differences were (get that thought out of your head, or your wife will

)

I'm going to dino because I drain it quite often since I drive through water and put the diff under I'm getting some water in my oil. It's just to hard to dump $30 worth of syn oil

I'm sure that syn will make everything last longer and run cooler, but for MPG-save your money.

Brian

 

[kruL]

I posted this in another thread so I hope it is not considered improper to repost it here...

Here in Atlanta, word on the street is "fear the OEM synthetic gear lubes". Several rearend shops report much higher failure rates with synthetic dope than conventional. Many refuse to use any brand of synthetic to avoid the extra risk of falure.

My source on this is a guy who has been doing gear sets and total rebuilds of RWD axles for many years. He does 200-300 of them a year. From 50's Chevys, including early Vette rears to monster 4x4's to classic musclecar 12 bolt conversions and even regular late model trucks, suv's and vans.

His personal failure rate is 3 rearends gone bad out of over 1,000 that he has at least put a new crush sleeve in, where most are either gear replacements and/or new bearings. He's good and many gear changes he has success with are used gear swaps from a different rearend. You have to be good to have zero failures from using used gears you know.

While no explaination exists for why there are so many failures associated with synthetic gear lubes, whether real or not, there is apparantly enough rumors going around where many who rebuild rearends for a living, at least in this area, are refusing to use any sythetic.

My friend recommends 20k changes of the dope with convetional fluids for 3.55 ratio's or higher. He likes Valvoline but is fine with any major brand. But for lower gears like 4.10, he recommends more frequent changes if you ant to see 300,000 miles of service.

 

[mechtech]

krul - Does your friend recommend the use of detergent oil yet?

 

[Dick in Falls Church]

A couple pints or quarts of synthetic gear lube vs non-synthetic gear lube isn't likely to give you whiplash at the stop sign, or a great increase in fuel economy.
Would I change? You betcha! SEcond the recommendation to use the SVG 75W-90 rather than the 80W-90. Better formulation.

 

[Eddie]

I checked my Subaru Forester for millage improvment after changing the engine/AT/ and both differentals to Mobil 1. The measured increase was 3% with a standard deviation of~1%. I ran my test for about 5,000 miles to generate the data. So expect an increase of 2 to 4% IF you change engine/transmission and differentals. I suspect that the engine contribution was ~2%.

 

[bulwnkl]

We switched a couple of our farm pickups to RedLine 75W90 in the front and rear axles, and D4 ATF in the transfer cases several years ago (I no longer farm). They were Dana 44 and Dana 60 axles in 1/2- and 3/4-ton 4WD Dodge pickups. Saw no increase in mpg. In fact, I thought I was able to just barely show a decline in fuel economy after the switch. However, I felt it was worth it to take the hit because I was operating half the year in Yuma, AZ, and towing extremely large/heavy equipment with it several times a year.

 

[kruL]

quote:

---

Originally posted by mechtech:
krul - Does your friend recommend the use of detergent oil yet?

---

He uses Valvoline regular GL5 dope in the quart bottles exclusively.

He does not like the idea of 5 gallon buckets because there is a much greater chance of contamination like dirt getting into the oil when you try to dispense it.

And while he does enough business to justify a 55 gallon drum and automatic hose fill system, he doesn't like that idea either because it might take several months to dispense a whole drum. He buys a few quarts every few days from Autozone so there is no question about "fresheness" or shelf life.

20+ years ago he worked for a guy who ran a rearend shop. That dude bought a couple of drums of dope for real cheap when another local shop went out of buisness... After a dozen burnt up rearend warranty repairs, they figured out that it was GL1 and not GL5 dope.

In short, they had to dispose of all of it as there was no one they knew who could have used GL1.

So to answer the question about the detergent... is Valvoline conventional dope considered a "detergent" oil?