In general, does changing out the dino gear lube in a RWD car and replacing with synthetic gear lube help, hurt or make no difference in regard to MPG?
Synthetic gear lube and MPG
- Thread starter mikeinaustin
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I do all of my vehicles. My Yukon XL MPG increased just over 1 mpg but I did the whole drivetrain. So, yes there is a slight payback in some vehicles.
Maybe some don't expect much. Sometimes replacing fluids can hurt your mileage as the new fluids are thicker than their used, sheared, counterparts.
Kestas
Staff member
Look at it this way -- I heard OEM has started putting synthetic in differentials to help with CAFE ratings, so it must have some beneficial effect. OEM must run the fluid it specifies for EPA qualification.
Considering the switch to synthetic is so cheap for 1-2 qts, and a long change interval, synthetic diff fluid is good bang for the buck with regard to fuel economy when compared with synthetic motor oil or synthetic transmission fluid.
I'm not a huge proponent of synthetics. But I find it hard to argue against synthetic for differential applications.
Considering the switch to synthetic is so cheap for 1-2 qts, and a long change interval, synthetic diff fluid is good bang for the buck with regard to fuel economy when compared with synthetic motor oil or synthetic transmission fluid.
I'm not a huge proponent of synthetics. But I find it hard to argue against synthetic for differential applications.
I changed the engine oil, transmission oil and differental lubs to Mobil. I did a before and after and measured fuel mileage for ~ 1000 miles before and after. The improvemant was 0.4 mpg with a SD of 0.13. I will never never make up for the increased cost of the synthetic fluids unless I run a 3X longer change interval.
I have never noticed any worthy increase in mpgs running syn oils as compared to modern oils.
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Originally Posted By: Steve S
I have never noticed any worthy increase in mpgs running syn oils as compared to modern oils.
^^2nd
I have never noticed any worthy increase in mpgs running syn oils as compared to modern oils.
^^2nd
On generator units (Caterpillar 1250 KW 3516's)in field use we recently found a statistically significant 3.3% difference in average fuel economy between a PAO/Ester based synthetic oil and a group II+ based oil of the same grade. This was a randomized trial with solid baseline data and loads were monitored for significant deltas. The synthetic oils advantage was consistent throughout the monitoring interval. Interestingly the Group II+ performed more poorly after it had a number of hours on it. Mind you the sump volume for these massive motors was 106 gallons of oil (including the filter volume) so the scale up to passenger car situations with varying driving styles and idle times is a stretch. In theory, at least, high quality synthetic oils will offer a slight economy advantage. I have yet to study whether or not group III oils are at parity with true synthetic oils in this regard. Any tribologists out there want to venture a hypothesis on this?
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What were the ambient temps?
Summertime desert conditions that ranged from 50-107 F. It was a [censored] place to have to work outside and log data/audit the study conditions.
I noticed a drop in diff oil temps (about 15 degrees) going from a conventional to a syn in my '86 truck. I guess I can't say precisely that resulted in a gain in mileage, because I didn't check, but less heat is less friction, yada-yada. I switched from one brand of synthetic diff gear oil to another an noticed zip. At the same time I switched out the rest of the drivetrain from semi-syn to full and again noticed zip.
dnewton3
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I completely agree that synthetics offer some advantage in fuel savings.
The problem is that for most people, driving is such an erratic event. I'm not talking about road-rage, but just the variability of daily routine driving. You'll never idle, accelerate, pass, be passed, drive up/down the same hills, the EXACT same way each time, with the exact same route with NO deviation for EVERY tankfull. So you have very little true frame of reference to make a call. If you put synthetic fluid in the rear diff, you're likely to get some benefit, but it will be masked by the variability of daily life.
The savings can be shown in static, controlled experimental environments. And the implication is that the savings can be transfered into typical daily use.
If you take each fluid, and take the claims of several lubricant manufacturers, you'd be suprised what is "possible". But there is a big difference between "possible" and "probable". Consider a fuel savings of 3% with synthetic diff fluid, 3-5% for engine oil, 2% for tranny fluid, and who knows what for synthetic grease in the U-joints ... it all adds up quickly.
Unfortunately, the "math" and reality don't always ring equivilant in concert. If you use synthetic fluids throughout, you could THEORHETICALLY get around 8-9% savings, but the reality is that it isn't near that much. Plus, some vehicles already come with synthetics and/or low viscosity fluids, so there isn't really anywhere to move towards. Consider the newer Corvette's. They come with Mobil 1, DEX VI, and the GM grapejuice diff fluid. That's all either synthetic stuff or low vis stuff, straight from the factory. So there is no savings to move towards.
Overall, you'll gain some small fuel savings if you convert the diff fluid to synthetic, but it'll not be enough to convince you one way or another if it was worth the effort. The main benefit to synthetics are extended service life and some ability to negate temp extremes better than dino fluids.
The problem is that for most people, driving is such an erratic event. I'm not talking about road-rage, but just the variability of daily routine driving. You'll never idle, accelerate, pass, be passed, drive up/down the same hills, the EXACT same way each time, with the exact same route with NO deviation for EVERY tankfull. So you have very little true frame of reference to make a call. If you put synthetic fluid in the rear diff, you're likely to get some benefit, but it will be masked by the variability of daily life.
The savings can be shown in static, controlled experimental environments. And the implication is that the savings can be transfered into typical daily use.
If you take each fluid, and take the claims of several lubricant manufacturers, you'd be suprised what is "possible". But there is a big difference between "possible" and "probable". Consider a fuel savings of 3% with synthetic diff fluid, 3-5% for engine oil, 2% for tranny fluid, and who knows what for synthetic grease in the U-joints ... it all adds up quickly.
Unfortunately, the "math" and reality don't always ring equivilant in concert. If you use synthetic fluids throughout, you could THEORHETICALLY get around 8-9% savings, but the reality is that it isn't near that much. Plus, some vehicles already come with synthetics and/or low viscosity fluids, so there isn't really anywhere to move towards. Consider the newer Corvette's. They come with Mobil 1, DEX VI, and the GM grapejuice diff fluid. That's all either synthetic stuff or low vis stuff, straight from the factory. So there is no savings to move towards.
Overall, you'll gain some small fuel savings if you convert the diff fluid to synthetic, but it'll not be enough to convince you one way or another if it was worth the effort. The main benefit to synthetics are extended service life and some ability to negate temp extremes better than dino fluids.
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Good post dnewton3.
I don't think the use of synthetic fluids is so much a function of saving fuel but more for protection in extreme temps, longer change intervals and better functioning of components, such as my manual trannies in my car and truck. My truck came from the factory with synthetic 75W-140 for the rear diff. Yet the front diff had a dino 75W-90 fluid. My front diff now has Schaeffer's Syn Blend and the rear has fresh Motorcraft syn diff fluid.
Whimsey
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