Ok guys, this may be a silly question but:
I have 21K on my truck and am about to do Engine, transfer case, diff lube change. Will any lubes get me better gas mileage? I do not do any heavy towing or extreme driving and live in a very mild climate. But I don't want to void my warranty either.

Probably nothing you would ever notice for mileage. I'd recommend synthetics. As long as you stay within spec requirements, they won't hurt the warranty.

If you go with synthetics all the way through on everything including the power steering you may have a slight increase and it might not even be measurable on a light truck. There has been extensive studies on over the road trucks that have shown an increase in mileage. At lot of the mileage claims are all hype and marketing, but they are absolutly better for your componets.

I've read somewhere (here in the forums) that staying with the lower viscosity (75/90) rather than the higher (75/140) actually does have a slight MPG advantage, and no warranty issues.Just my 2 cents but what do I know:idea:

I've read somewhere (here in the forums) that staying with the lower viscosity (75/90) rather than the higher (75/140) actually does have a slight MPG advantage, and no warranty issues.Just my 2 cents but what do I know:idea:



Lighter is better as you stated and is well within GM specs. You really only might consider the heavier oil if your doing a lot of heavy towing.