A relative of mine has a '96 C2500 with a 350 and 104K miles. The truck runs perfectly but something that I've found odd since he got the truck a little over a year ago is that the tailpipe started getting very black. The truck functions as a daily driver going to and from work which is about a 24 mile round trip that is mostly 70 MPH freeway. Recently we took a longer road trip to pick up an older small engine and the truck got 15.3 MPG (mostly interstate driving). It hasn't had any codes or lights come on in the past year that he's owned it and it has been very reliable. It's not that big of a deal really, but I have to admit it bothers me that something might be going on.
What are your thoughts?
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Your mpg (gas) sounds very good.
But how about the MPQ? (Miles Per Quart of oil?) Some oil consumption is to be
expected, but it does vary from one engine to another.
And one other thing to look for is any consumption of engine coolant that's not an
external leak? Note: Some oil consumption is OK, but zero coolant consumption is
the only right answer.
As an aside, I used to see really clean exhaust back when AIR pumps were being
used? The assumption here is that because they would continue/finish the burn
in the exhaust system there wasn't very much left over for visible deposits at
the tailpipe?
EDIT: Climate plays a part in how the tailpipe opening presents. Driving in a bone
dry climate where you never see the morning cloud of condensate escape as you
drive will give you a different look as compared to living in an area where there's
a lot of humidity and temp swings.
One last thing. Cleaner tailpipes will be found on low mileage vehicles with good
maintenance, rock-solid closed loop operation, healthy cats, & very low oil consumption.
The GMT400 fleet is anywhere from 22-36 years old, so if your buddy is getting
15+ mpg on the highway, oil consumption is below his threshold of pain, and it isn't
consuming any coolant, then life is good, and a little soot in the tailpipe would
not be a concern.
Hope this is helpful --
