Will synthetic differential oil give better fuel economy? - PeachParts Mercedes-Benz Forum

funola · #1 11-24-2010, 09:51 AM

I've put 50K on my 300DT since purchase and don't know when the diff oil was last changed. Should I go synthetic or regular? Pros and cons? Your experience?

andrewjtx · #2 11-24-2010, 09:55 AM

I changed from regular to royal purple syn, no difference noticed.

79Mercy · #3 11-24-2010, 10:01 AM

I put Mobil synthetic in my 79 280CE, i couldn't tell any difference.

Bio300TDTdriver · #4 11-24-2010, 10:04 AM

Quote:

Originally Posted by andrewjtx

I changed from regular to royal purple syn, no difference noticed.

X2

Hit Man X · #5 11-24-2010, 10:36 AM

I would just pump it full of dino oil and get on with life. Save the money to buy yourself a burger, onion rings, and a beer.

andrewjtx · #6 11-24-2010, 10:38 AM

You have to look at it like this, you're just lubricating straight gears. There are no valves and pistons (like the tranny) or bearings and pistons like the motor. So long as you have the right weight, the diff will function the same.

The reasons for switching to syn would pretty much just be for better protection and to lengthen the service interval.

Hit Man X · #7 11-24-2010, 10:48 AM

Well GM and Ford both called for syn rear oil in two of my trucks... and the Ford is very heavy at 85/140. I can only assume for the Ford, it came with it for maximum protection when towing huge loads and not for fuel economy as it is exempt (not sure what is called for on the half ton Fords)

The GM I would think for fuel econ at 75/90 BUT since it is 4x4 and the hubs are always locked I cannot see that, plus the front calls for 80/90

Anyway, I stick by my original statement in the MB.

Just remember, most people never service the trans, let alone the diffs... so just doing that is a good move.

vstech · #8 11-24-2010, 11:04 AM

I see it like this.
the differential is the load distributer of the engine's output... fresh oil removes moisture and wear particles.
synthetic oil handles both well AND it is better at shear loads.
I doubt it makes a hill of beans difference in fuel economy.
perhaps over the life of the car, it'll save a hundred gallons of fuel...

Jeremy5848 · #9 11-24-2010, 11:56 AM

Because synthetic oils are made to have smaller molecules (this is why they have better cold-flow characteristics) they will leak out of tiny gaps that dino oil won't. When I put Mobil-1 synthetic diff fluid in my '85 300D-T (W123, OM617), it would drip one drop of fluid every few months. The diff cover has no gasket, you know, and sealing depends on the metal surfaces plus whatever sealant you put on them. There might be some advantages in extremely cold climates but I don't see any improvements in fuel economy measurable by normal drivers.

barry123400 · #10 11-24-2010, 12:01 PM

Temperature depenant as well.. If you see normal gear oil in a differential at lower temperatures. Until the rear end warms up the crown gear just cuts a path through the congealed lubricant so the presence of lubrication on the crown gear is not there. Actually the crown gear looks totally dry.

There are pictures of this during rear end testing. I just do not know how low a temperature this is present at. So the synthetics should add some additional life over the years where the seasonal temperatures drop off. Since it is not changed out often the additionl cost is not signifigant. In what we reffer to as southern climates possibly little if any advantage.

Gain in fuel milage lubricant dependant? You probably could not find any if you tried or a very small insignifigant gain with the synthetic.

roundout · #11 11-24-2010, 12:19 PM

No difference in my 300D. I switched to all synthetics in a 2001 Camry I used to own and picked up a couple mpg on average.

#12 11-24-2010, 02:17 PM

I believe it would, but it would be a fractional and unmeasurable amount that would probably never return a savings equal to the initial cost.

Hope this helps.

ConnClark · #13 11-24-2010, 04:30 PM

I agree with Larry to a point.

It should reduce drive train losses a hair and thus put more (although insignificant) fuel energy to the road.

I went with Mobile 1 synthetic gear oil when I replaced mine. It wasn't that much more and it will probably pay for itself in fuel eventually but I'm more concerned with wear and tear protection.