Friend of mine in a rather large GM maint shop has told me several times over the years to never change to Synthetic until at least 15K miles on a new engine. He said they have pulled more motors than you could imagine when people switch earlier than that .....

 

Synthetic is always the way to go. Maybe not with a 100k oil leaker but you still can get more life out of a 40 or 50k engine with synthetic. I would use it in the diffs and tranny too.

 

Thank you all for your input. I'll call this morning and make sure they do synthetic. This is the first car of the maybe 12 I've owned that I have never changed it myself, mostly because they dealer is cheap where I go and it's more convenient to get it done every time something breaks

I want to switch to synthetic on the diffs and manual tranny as well, but they want like $400 or so bucks to do it, but I have a hard time believing I can't do that myself. I know how, but am a little paranoid about doing it on the differentials. I've done it on manual transmissions with the gear oil and It's always been a pain to get it in the hole.

If I keep the truck, I'll probably get everything soon. I guess it's a good idea to switch all the fluids at 50k miles.

 

My CTS used Mobil 1 from the factory. I changed to Mobile 1 at my first oil change in the H3. Changing oil in the H3 is not easy so prolonging the intervals is nice.

 

I was going to have them put Synthetic in, but just found out they want $50 more for it. That's kinda crazy to me. I can go buy 6 qt.s of oil at $4 or $5 and do it myself, but the normal change is only about $25 for me, so that's why I keep using them. I'll definitely change it myself the next time though.