Does anyone have any experince with synthetic gear oil (for differential), specfically (sp?) if it helps out gas milage as Mobil 1 75-90 claims?

Do you guys think that 75-90 syn would be a acceptable subsitute for conventional 80-90?

 

I changed over to Mobil One synthetic gear oil in the BMW about six months ago. I monitor gas mileage very closely. There has been no measurable improvement.

According to RedLine, mileage gains from synthetic oil in the diff are primarily at low temperatures. That means that if you do primarily short trip driving in a colder climate, there might be an advantage.

Synthetic has a higher viscosity index, hence the 75W rating instead of 80W.

BMW calls for a diff fluid change at every tuneup with conventional. I am going treat the Mobil One as a 100,000 mile fluid in that car, which will more than justify the added cost.

Jim

 

I have used syn 75-90 for several years in a 94F250(lots of towing 8,000#+), and a Chebbie both with limited slip. Also older cars 79TA, 86 Turbo Coupe. Never had a problem. Never had problems with dino either, so no real proof other than magazine articles.

Check the bottle, some synthetics are not recommended for use with limited slip. Others should have the limited slip additive put in with the lube. I use Sta Lube Traction Lock additive, meets Ford and Chevy spec. I use both Valvoline and Mobil 1 gear lube. A chebbie web site I am on recommends 2 bottles of additive with synthetic, this helps eliminate chatter. Works for me.

I keep pretty good records, but any gas mileage difference would be small and lost in the noise. I have read that Syn in engine and tranny and diff might give you a mile or two improvement but my mileage can vary a mile or two depending on driving and since I live in Oregon(we are too Stoopid to pump our own gas) it also depends on whether the **** filling the tank fills it the same every time.

In my opinion syn is great for extended drain periods and that extra margin for low temp and high temp. I think it would be difficult for the average owner to prove any API/SAE approved lube has damaged their drive train since it takes so long for damage to occur in normal cases.

I will say the syn lube is much easier to pump into the diff. I used to get cramped arms pumping dino into the diff. Now with syn it is easy. Syn is much thinner and will flow at low temperatures, this can make a diffence if you drive a lot of short trips in cold weather.

Just my opinions

Jim Henderson

 

SuperClint, methinks it would help a little. Would it be enough to notice ? Well thats debateable. But I think it is a good idea anyway. How cold does Rapid City SD get ? I remember driving my 4wd F100 in Michigan in the winter. It got as cold as -15 that I remember. Going down the road when the tranny was cold (NP435) it was almost impossible to move the shifter. I went in 2nd for at least a mile before I shifted. After everything is warmed up, it went back to feeling normal. When looking at how easily M1 15W-50 pours out of the bottle compared to the 20W-50 valvoline I had been using, the synthetics wins hands down for the cold weather stuff. I plan on changing to synth in the tranny, T-case and axles as soon as they need changing. DF

 

> SuperClint, methinks it would help a little. Would it be
>enough to notice ? Well thats debateable. But I think it is
>a good idea anyway. How cold does Rapid City SD get ? I
>remember driving my 4wd F100 in Michigan in the winter. It
>got as cold as -15 that I remember. Going down the road when
>the tranny was cold (NP435) it was almost impossible to move
>the shifter. I went in 2nd for at least a mile before I
>shifted. After everything is warmed up, it went back to
>feeling normal. When looking at how easily M1 15W-50 pours
>out of the bottle compared to the 20W-50 valvoline I had
>been using, the synthetics wins hands down for the cold
>weather stuff. I plan on changing to synth in the tranny,
>T-case and axles as soon as they need changing. DF


Rapid City has one of the weirdest weather patterns in the US, 4 days ago I was riding my motorcycle with just a sweatshirt (65 F), next morning it was 0 F , not counting the 20mph winds. But South Dakota can and usually does, stay well below zero for a couple of months at a time. Last year the warmest it got in Jan-Feb in the NE part of SD was 0 F.:-X12

I just pulled out my open carrier and replaced it with a LS carrier in my ranger 8.8 rear end, and filled it with 80-90 conventional and somefriction modifier for the LS. Next afternoon I thought to my self that maybe I should have used a synthetic like Mobil 75-90, thus my question that I asked.

I'm still thinking about pulling the conventional out and replacing it with synthetic.

BTW, thanks for the replies!

 

I would say you might get .00001 MPG improvement. A good synthetic would help you with changing intervals and if you do any towing or heavy hauling it could help keep the heat down a little in the tranny and diffs but other than that I can't see huge improvements in MPG and overall wear if you do regular changes.

 

I changed out the regular gear oil in front and rear diffs a month ago with Mobil 1. Old oil was about 50,000 miles old, looked clean, and took a while to drain (thick!). No noticeable difference in mileage. The only things that I noticed were less "drag" in the cold mornings when driving the first mile or so as well as the rear pinion seal started leaking a week ago. Pinion seal only leaked when parked downhill though and left a noticeable quarter sized puddle on ground after 2 hours - so I guess Mobil 1 really does flow better! My truck has 120,000 miles and it was the first time pinion seal leaked so maybe it was a coincidence and due to happen anyway...

 

I am in the process of finishing up a thorough "going through" on my truck. When I got done with the front and rear axles I replaced with the Mobil 1 75W90. I found with conventional 80W90 that on real cold mornings that I had to engage the front axle just to get the thing moving. I typically keep my front hubs engaged all winter long and if your sitting on a slick street the added drag of the thick oil in the front end is enough to spin the rear. Everything loosens up after a mile or so and then I can disengage. My hopes is that with the better cold flowability of the Mobil then stuff will move easier.

Randy