My truck just rolled over 50K miles, so I figure that it is time to get the diffs serviced. Is there any advantage to running synthetic fluid in the front/rear ends? What types/weights would you recommend? The truck is an 03 1500HD 4x4. I'm thinking that I should also check with Chevy because the truck has a factory rear "locker" and it might require a certain type of fluid ???

Mobil 1 Synthetic 85w90, pick it up at any auto parts store. The G80 rear slip doesnt need any special additive or crap that the dealer may tell you, but toss in Mobil 1 for sure. About $8 per quart.

Will do! I run Mobil 1 fully synthetic motor oil and I have always had good luck with it. Thanks!

I noticed after autocrossing my Camaro all day, the diff (with dinosaur oil) was too hot to keep my hand on the cover , but stayed noticably cooler when I put in synthetic.

Just my personal experience. I never measured the actual temps. I'm guessing 20-30*F difference.

X2!!
I run it in Everthing!!
A little hard on the pocket book but, So are Gears!!

Double check your owner's manual. A lot of the newer trucks that I have seen lately have come with synthetic oil from the factory.

Regardless of what the factory put in it, I would always put synthetic in mine. I've always been partial to Mobil 1 because of its availability over Amsoil but either one would do well for you.

Double check your owner's manual. A lot of the newer trucks that I have seen lately have come with synthetic oil from the factory.

Regardless of what the factory put in it, I would always put synthetic in mine. I've always been partial to Mobil 1 because of its availability over Amsoil but either one would do well for you.

Same here even though I was an Amsoil dealer for 7 years.

I run Amsoil synthetic in the diffs of everything I own. The cooler temps and the WAY better wear are what did it for me. I run Amsoil 75w90 severe gear in just about everything I own. Mobil 1 is good too, but for God's sake, do NOT put the factory crap back in that truck. If you look at this white paper on gear oils, you will notice that lucas, as well as Mopar and GM synthetic lubricants did really POORLY. Amsoil didn't score the best in each, but overall, IMHO is the best to go with. If I wasn't a dealer though, and couldn't get it easily, I would probably go with Mobil1. Of course, if you decide to go with Amsoil, I can get you a good price :D

http://www.amsoil.com/products/gearlubes/WhitePaper.aspx
Scott

Double check your owner's manual. A lot of the newer trucks that I have seen lately have come with synthetic oil from the factory.

All the newer chevies arleady run synthetic gear oil in the rear, that is true....BUT not in the front case or trannies. From at least the last 10 yrs.

yes, but... if you look at that white paper I posted a link to, the Mopar and GM synthetics did pretty bad in the tests...

yes, but... if you look at that white paper I posted a link to, the Mopar and GM synthetics did pretty bad in the tests...


A little OT but after looking at those tests I like how Lucas did the worse. :D

Even with a grain of salt.

I've liked synthetic in my 4 speed in the winter so I can actually shift. But then the synchros just don't work as well. I've also noticed the syn holds up better after long trips.

All the newer chevies arleady run synthetic gear oil in the rear, that is true....BUT not in the front case or trannies. From at least the last 10 yrs.

Good point. I kinda forgot about that. I know for a fact that my dad's '99 F350 came with conventional oil in the front end and synthetic oil in the rear end.

You should be able to tell for sure how it came if you check your owner's manual though.

One interesting thing to note though is that regardless of oil type or quality I've only seen a few differential failures that can't be attributed to abuse or misuse. Think of all the cars out there from the '70s, '80s, and '90s that are still running the original diff oil with high mileage and no problems so far. It's not something I would necessarily do, but still is interesting.

Hmmm neighbour across the alley is an Amsoil dealer, wonder if he can get me the stuff in 5 gallon pails??

I've liked synthetic in my 4 speed in the winter so I can actually shift. But then the synchros just don't work as well. I've also noticed the syn holds up better after long trips.

FYI, one thing to be sure of when putting anything in a manual is whether or not you have yellow metals in the synchros, and if the oil is compatible with them.

VERY FEW gear lubes are compatible with yellow metal synchros!! Nissan's have them, and it is fairly common for people to put the wrong gear lube in and wipe out the synchro's. Here's another note, most people think all GL4 is compatible, this is completely wrong. If it says gl4-gl5 rated, it's 99.9% chance that it is NOT compatible. If it's GL4 only, there's still about a 95% chance it's not compatible.

We were at 12 parts stores yesterday trying to find some that was, and NONE of them had it.

I run amsoil MTG in my tranny just for this reason, it is one of very few compatible gear lubes. I run the 75-90 severe gear stuff in the t-case/front and rear diffs.

Hmmm neighbour across the alley is an Amsoil dealer, wonder if he can get me the stuff in 5 gallon pails??


If he can't get it for you, I can :)
Scott