Breakin - When????

[Srsmith]

I own a 2004 Sierra 2500 with the 6.0 liter engine. Bought from a friend. Is in excellant shape with a topper. It has 48,000 KM. My friend used regular oil until around 25,000 KM and then switched to Castrol Sytanx 5-30. He never felt like the vehicle broke in..He never say the increase in gas mileage as he had seen with his 99 Sierra. Currently getting around 10.2 miles per gallon in town...and not sure what I am getting on the Hyway...perhaps 13 mpg.
Would you think this vehicle is now broke in and I will never see much if any of an increase in gas mileage. I drive like a grandma.
If this is it...this is it..just a little surprized this vehicle gets such poor mileage.
Regards,
Sam

[Z15]

The 6.0L engine is notorious for poor fuel mileage, especially in the 2500 series. Although many claim to get a high as 15 mpg. So I would say that about all you can expect to get from a heavy truck like that.

You might want to check your tires though as they can have serious effect on mpg if they are underinflated.

If you are not hauling anything, the 2500 truck is a poor choice for a crusier.

Castrol syntec is not going to give you any better milage.

[Srsmith]

Mike,

Thanks for the input. I was not expecting any surprizing and hopeful relevations. I did not buy the vehicle for cruising. I bought it to pull an offroad tent trailer that weighes in at about 4500 lbs. Which with the bed loaded and pulling the trailer and 4 people...it pulls like there is no tomorrow!

Did not buy it to economize. I am in a position where I don't have to use it daily or driving long distances to work. I average about 100 miles a week at that.

In regards to tire pressure. I have OEM tires...believe they are 16's. Tire indicates i should run them with 80 psi. i am sure that's with a load. I currently run them at 50 psi. Would hope that is sufficient. Previous owner ran them with 50 psi and tire wear looks to be even.

Best Regards,
Sam