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post #1 of (permalink) Old 07-28-2003, 09:10 PM Thread Starter
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Semi O/T: Synthetic Lubricants

friend of mine has a question about synthetic lubricants and it's effect on gas mileage. even though he has dodge durango, i think that basic question about synthetics still applies to any vehicle. He writes:

Subject vehicle - 1998 Dodge Durango 4x4 (part-time) 5.2 liter V8 AT a.k.a. The Gas Hog

I'm going to have virtually ALL lubricants changed. So, we're talking both diffs, transfer case, transmission and engine. For the purposes of my question, let's leave out the front diff and transfer case, since I've engaged 4WD only 3 times in 5 years. In 2WD, the transfer case and
front drive train are dis-engaged.

Question: Will synthetic lubricants in the rear diff and AT result in better gas mileage?

Reason for asking: The shop is telling me that synthetic lubes will not improve gas mileage. I'm having a hard time with that. Lower friction means better gas mileage, right? Or is it not all that great a difference?

Our around town average is 13 MPG, and on the highway we're lucky to see anything better than 15. And the fact that
we drive on the highway at 75 MPH with the AC on doesn't help. But we're driving about 10K miles a year, so that translates to 769 gallons at $2.05 a gallon (current approximate price for mid-grade Chevron). Translating
further, that's $1,576 a year on gas. A 0.5 MPH improvement would save me $57 per year on gas. So it seems to me if I could upgrade to synthetic diff and trans lube for less than an extra $57, then I'd be money ahead.
Not to mention that my wife would not complain *quite as much* about filling the tank on this tank.

So what do you think? Anyway, if anyone has direct experience with measuring gas mileage after switching driveline lubes, please share.
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post #2 of (permalink) Old 07-28-2003, 09:15 PM
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Re: Semi O/T: Synthetic Lubricants

ya.. and when you put it in 4wd.. it'll work better [img]images/graemlins/chair.gif[/img]
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post #3 of (permalink) Old 07-28-2003, 10:38 PM
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Re: Semi O/T: Synthetic Lubricants

That $57 works out to a 3.6% savings on the fuel costs...factor in the insurance and the payments on a durango, and you're down to probably less than a 1% savings in costs on the vehicle...

however, i think that in the long run, synthetics are better for a newer vehicle than dino juice, correct? perhaps it will save on maintenance costs down the road? on a year over year basis, though, using the information supplied, i wouldn't consider it a significant impact...
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post #4 of (permalink) Old 07-28-2003, 10:43 PM
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Re: Semi O/T: Synthetic Lubricants

simpsons did it!

i mean err i think Hot Rod magazine did a dyno comparison and gas mileage differences of all natural vs all synthetics. ill try and find it.


"After a 5-mile jaunt to get everything up to the same temperature as the baseline test, we let it rip. The monitor read 418.4 hp and 411.2 lb-ft of torque, a gain of 10.1 hp and 6.1 lb-ft just by switching to synthetics"
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post #5 of (permalink) Old 07-28-2003, 11:42 PM
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Re: Semi O/T: Synthetic Lubricants

I'm wondering why you eliminated the front dif. If I recall the Durango has NO locking hubs ...aren't you still spinning the axles and the gears just like you are in a TJ or Cherokee?? (if I'm wrong please educate me [img]images/graemlins/chair.gif[/img])

Without going into all the this and that stuff ....I've seen not too much fuel economy change by switching my diffs to synthetic gear oil ..and my t-case to synthetic AFT. About the only measureable fuel economy increase that I have ever noticed was when I switch from passenger car synthetic (typically either supersynth or trisynth Mobil 1) to Delvac 1 synthetic diesel rated oil.. I've tracked the fuel economy on my wife's TJ for the entire 74,000 miles and have virtually filled it up every time at the same gas station one of two pumps that tilt somewhat down hill. She's gotten between 17-17.5 the whole 4 years that she's driven it. Upon the change to Delvac 1 ...she began to consistantly break 18+ for the past 6k.

I'd say that if you're looking for savings will probably not find it. I'd say if you can break even ..I'd go with the synthetics just because they're better for all components ..especially if you have any extreme climates (or a 4 seasons climate). They are just so stable when compared to dino. (but the gap has narrowed somewhat has the price)
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post #6 of (permalink) Old 07-29-2003, 07:11 AM
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Re: Semi O/T: Synthetic Lubricants

[img]images/graemlins/tongue.gif[/img] When I was preparing our FS GM 3/4T 4X to do something that we shouldn't, I was sweeping out every performance and durability corner possible to give it every advantage. Knowing that we had the 8900 Ft. pull over the Sierras and the Rockies after that, I opted to put synthetic lube in the newly rebuilt tranny and transfer case, AND the 14-bolt FF rear end. The highest oil temp I observed on that rear axle with the GM 350 at 3900 RPM with the main box in second and the t-case in "under" at 12 MPH on a very steep grade for almost 30 minutes was 265 degrees F.......not bad at all. Now the DOWNSIDE was that by putting the synthetic in the main box, the SYNCHROS don't work as well, and you acually have to "understand" the box to shift it well; especially if you are shifting without the clutch as I so often do. You cannot just push into the next gear because the synchro won't help you.....the lube is too slick for it to work right. The synchronizer elements "wring" together and won't let you slide into the next gear. This is NOT a problem for me since I drove trucks before they even HAD synchros, but I wanted to mention it anyway so you could be aware. [img]images/graemlins/tongue.gif[/img]
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post #7 of (permalink) Old 07-29-2003, 10:43 PM
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Re: Semi O/T: Synthetic Lubricants

Let's look at it this way.

10k miles a year, that's 3 oil changes.
Synthetic will cost about $15 more than regular oil. That's $45 extra for engine oil. So now your savings is $12 a year.
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