Synthetic gear oil question

[KyDan]

I have an 04 Chevy Silverado.
If I change the rear differential oil will it run cooler using
full synthetic?

Has anyone here changed to synthetic gear oil?
Any links to testimonials or test results?

Thanks!

[LadyWindrider]

Check your manual. My 01 Ford F150 came with synthetic in the rear diff, and the manual states not to do anything ever to it. I would have thought Chevy would have caught on, but I don't know. As for running cooler, have no idea. In my thinking, no. There is really no way to cool the diff fluid. I guess if it cut down on friction, it wouldn't generate as much heat. Just my 2 cents.

[NWJeeper]

We tried running synthetic in our Jeep differentials as they really see a lot of abuse but for that reason we ended up having to change it a few times a year too so it didn't work out to be worth the money. I run Lucas gear oil in all our differentials and in the final drive of the outboard motor on the boat. In the case of our Jeeps and the last motorhome I did notice less noise with the Lucas oil but I don't believe it's synthetic. My mind isn't convinced that the synthetic is better for the money spent.

[KyDan]

What got me thinking about this is some months back a poster here
said the "pumpkin" had gone out in his Chevy Suburban.
I don't remember if he said anything about synthetic or not.

The only reason I would change it would be if it was supposed to
reduce friction and heat.
Also synthetic does not thin out as much when it is hot.

I'll read the manual and see what they recommend.
I was just wondering......

After my last trip a couple days ago-
100 miles on interstate at 65 MPH and air temp of mid 60s.
When we got home after about 10 minutes I thought about
this and crawled under the truck.
The diff was hot, like a car hood on a hot sunny day.
I could leave my hand on the rear cover but it was mildly
uncomfortable.

I guess this is normal.

In June we plan a big trip to the south west.
We'll have days of many hours of Interstate at temps in
the 80s.
Just wondering if a gear oil change would make any difference.

I know asking a question like this is like asking
which tires are best or
which engine oil is best.
EVERYBODY has an opinion!!

[NWJeeper]

Yeah, the diffs being hot is normal. For rigs that see lots of harsh conditions, like our Jeeps or tow vehicles doing a lot of pulling I think the best advice is what mechanics will always tell you. Keep the fluids changed and clean. Some diffs are easier to change the fluid on than others. Ford's 8.8 axles (of which I have under the rear of my Jeep) has a convenient fill hole up high in the front. Many of the Dana axles have a single fill port put you either have to loosen the cover bolts to drain them or pump the fluid out through the fill hole. I have replaced the covers on my Jeep with heavy duty covers that have drain and fill plugs built in, makes it really easy to change the fluid. If it were me and I was towing a lot I would change my diff fluid at least every other year for piece of mind. It's not all that expensive and the oil you choose to run as long as it meets specs is probably not all that important.

[Dave_Monica]

For the small difference in cost as you only need about 2 liters, I'd recommend going with the synthetic. No one will argue that's it's the best for reducing friction. That's what I use in the diff. of my drag car.

If you're adventurous, you could drill and tap (1/2" NPT) in a low point on the differential to make future changes a lot easier.

Dave

[EXGMTech]

all the newer GM's use synthetic from the factory...pretty expensive- $30 per bottle...rear diff takes 2 1/2 bottles

[acadianbob]

Some people have reported better fuel mileage; especially in winter when lubricants are thick. There are also "watchouts". If you have a locking rear differential, my understanding is that they require a special lubricant with "friction modifiers". The F150-Online forum mentions this. Frankly, I wouldn't pursue synthetic in differentials and transfer cases unless you live in a cold climate.

Similarly, I used to be a user of synthetics in my engines for years. They do have better cold start advantages IMO; but I'm talking 0 degrees or colder. Recently, I've gone back to Ford Motorcraft oils and filters and they work just fine. I go 5,000 between changes and it never moves off of the full mark. The Oil Guy tests (google him) show that Motorcraft holds up extremely well and is a lot more cost effective.

Not knocking synthetics, I think they are superior. The question comes down to whether you really need it and the cost effectiveness. If it gives you extra peace-of-mind, then it may be worth it.

[NWJeeper]

Originally Posted by acadianbob

There are also "watchouts". If you have a locking rear differential, my understanding is that they require a special lubricant with "friction modifiers".

More accurately friction modifiers are required by some manufacturers if you have a limited slip differential, not lockers. LSD work on an internal clutch system in the diff that senses the loss of traction and locks up and they do require friction modifiers. True lockers (Toyota TRD, newer Jeeps with air or electric lockers, Eaton E-lockers, ARB air lockers) do not use friction modifiers as they have no clutches. When a button is pushed they lock the axle solid like a spool.

Your owners manual will state if you need a friction modifier. You add the modifier to regular gear oil and it usually comes in a smaller bottle or tube.

[TravelSoftballDad]

"What got me thinking about this is some months back a poster here
said the "pumpkin" had gone out in his Chevy Suburban.
I don't remember if he said anything about synthetic or not."

That was me ;-(

Synthetic came OEM in that diff from Chevy...and it burned up good. Following the warranty repair service, I actually drained the new replacement oil and went to AMSOIL Synth Gear Oil after doing a bunch of research. I love it ! I learned a lot from that whole ordeal.

I added a Mag-Hytec diff cover (holds more oil, has magnetic dipstick, and a drain hole) and strongly recommend them to others. Since going to AMSOIL, I check the color and levels quarterly. To date (well over a year), the AMSOIL gear oil is still golden colored and is working like a charm.

To be honest, since that pumpkin nightmare and my AMSOIL trial(s), I have switched both vehicles over completely to AMSOIL. I guess I would be considered an AMSOIL Kool-Aid drinker, but I've tried several products and am sold completely.

Some testing of gear oils :

http://www.amsoil.com/products/gearl...hitePaper.aspx

http://www.amsoil.com/lit/g2457.pdf

Hope that helps !!

[TravelSoftballDad]

Sorry....forgot to add something. It's normal for the diff to get too hot to touch. However, and those who have experienced this can verify, when gear oil starts to burn, it smells really, really bad. It does not smell like 'regular' burning oil...it's got it's own nasty smell.

[KyDan]

I got out my owners manual and I still have the window sticker
from when it was new.
The owners manual says use GM part # blah blah....
I'd rather use aftermarket synthetic.
The window sticker says I have a "locking rear axle".

I know it's not the kind that people who go off roading have
that literally locks into a solid axle.
So what is it??? I think it's got clutches.

My real question is this-- If I drain and refill it with Royal Purple
synthetic 75w90 do I still need to add the K & W Posi trac additive?
I guess I'll give the folks at Royal Purple gear oil tech line a call....

[EXGMTech]

it's kind of the best of both worlds...I call it a posi-locker...you have an "open" rear until there's wheel spin then the centrifical mechanism locks and it becomes a posi..yes there are clutches. This way you don't get the chattering around corners like the old posi's did

[KyDan]

Never mind-- I found the answer to the additive at the Royal Purple
FAQ for gear oil--

"Max-Gear is recommended for use in truck, motor home / RV, and automotive front or rear differentials, manual transmissions, and lower gear units of marine engines that specify use of an API GL-5 or GL-4 fluid. All viscosities of Max-Gear are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary."

[KyDan]

Thank you!!

[MaxPe]

I have been using royal purple throughout my Trailblazer SS drive train for the past 50,000 km except for the transmission since they did not have anything rated for my transmission. I did some research on the products before I switched and found the info positive.

They advertise lower coefficient of friction which equates to a decrease in oil temperatures (how much I don't know), less wear, better thermal wear and breakdown of the oil, higher boil off temperatures, longer intervals between oil changes (oil filter every 4000 km) and better cold start properties. I am definitely going to check out my rear differential after a drive on the freeway and see how warm it is.

Over all I am happy with the fluids. One thing I also did was change out my transfer case fluid to the same fluid I use in my engine which is the royal purple 15w-40 oil instead of the fluid recommended by GM. Typical transfer case fluid can boil off just like transmission fluid and that's why your levels go down after some time. Check out the article for reasoning behind this. My dad has been a heavy duty mechanic for 50 years and swears by that info. I even use that oil in my 1300w generator and it seems to run a tick quieter then when I had conventional oil in it. I personally think anything with 5w in its specification should be left to oil up your hairdo for that slick look.

http://www.rsgear.com/technical/articles/2007_03.pdf

[SaskCampers]

Originally Posted by TravelSoftballDad

"What got me thinking about this is some months back a poster here
said the "pumpkin" had gone out in his Chevy Suburban.
I don't remember if he said anything about synthetic or not."

That was me ;-(

Synthetic came OEM in that diff from Chevy...and it burned up good. Following the warranty repair service, I actually drained the new replacement oil and went to AMSOIL Synth Gear Oil after doing a bunch of research. I love it ! I learned a lot from that whole ordeal.

I added a Mag-Hytec diff cover (holds more oil, has magnetic dipstick, and a drain hole) and strongly recommend them to others. Since going to AMSOIL, I check the color and levels quarterly. To date (well over a year), the AMSOIL gear oil is still golden colored and is working like a charm.

To be honest, since that pumpkin nightmare and my AMSOIL trial(s), I have switched both vehicles over completely to AMSOIL. I guess I would be considered an AMSOIL Kool-Aid drinker, but I've tried several products and am sold completely.

Some testing of gear oils :

http://www.amsoil.com/products/gearl...hitePaper.aspx

http://www.amsoil.com/lit/g2457.pdf

Hope that helps !!

I run Amsoil in both diffs and the transfer case on our 2008 2500 Ram Megacab so far so good. Also ran it in our 04 quadcab 4x4 that had 180,000 on it when we traded it in and the guy that bought it said he had never driven a new truck that felt any tighter. Mind you we are blessed with -30 to -40's in the winter here.

[dlstewart01]

GM trucks have had synthetic gear oil from the factory sinse 1998. All GM trucks with the G80 RPO code have a locking diff. No truck from GM is equiped with a limited slip diff with the exception of the Quadrasteer, which had a G86 limited slip.

http://www.youtube.com/watch?v=-sw9DwurQAs

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 75W-90 GL5 (P/N 12378261). The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 12678261 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
© Copyright General Motors Corporation. All Rights Reserved.

[gettmad]

That was great! Thanks for that. The youtube video I mean.