GC MPG and oil pressure.

I have about 600 miles on my 1st run of GC in my 2003 Silverado 5.3. So far in city I got 16.7mpg(about the same as M1 10w30) and I just did a 300 mile road trip and got 20.6 mpg doing 85mph!!!! This is pretty good for a V8 at any speed let alone 85mph and some hills! My all time best mpg with this truck was 21mpg with Mobil 1 10w30. So I think I still get the same MPG using GC as I did with M1. Oil pressure seems about the same at idle and speed. So only a UOA will tell which oil is the better in this engine. I will post it soon!


Staff member
Guelph, Ontario
Originally posted by JustinH: the way the GC works, is the first 1000 miles you will get better gas mileage, then it will thicken up and you will get worse gas mileagee.
Not true in my case. My GC did thicken up from 12.2 to 12.9 over a 6200 mile interval, but the gas mileage did not suffer.
Shippensburg, PA
On 2 fill-ups after GC, I am seeing an average .7-1 mpg increase over previous fill-ups with 10W-30 Pennzoil Dino. Car is a 1995 Mustang GT. I'm going to keep checking it, as I'm not convinced that 2 fill-ups is enough to get a "real" idea of MPG... too many other variables can come into play (wind, speed, etc). However, since this car has been consistantly putting up the same numbers while using dino, (within .5 MPG), my initial impressions are favorable.