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My 2001 Silverado 1500 (4.3L) with well over 330,000 miles on the ticker.
Last September - I had the transmission changed for the first time ( a rebuilt was installed by a national chain transmission shop).
I changed plugs/wires/distrib cap/rotor/ignition coil last August (1 year ago)
I change air filter annually (currently due - will change today)
Will be changing fuel filter this weekend when I change oil/oil filter
When my father gave me this truck several years back - I was getting between 19-21 MPG on average. Over the last couple of years - that has tanked down to about 13.5 to 14MPG (as of my last 2 fill-ups). I also have to add about 1qt of oil for appx every 1000 miles I drive. It doesn't leak to the ground - I think it's consuming the oil. (valves out of spec? cylinder rings leaky?) I have not done a compression test yet - maybe later in the fall after it's cooled off a bit. I HAVE been running the A/C (this IS Texas - 90-105 deg. F) - and the engine REALLY feels a change - like it's working harder when I run the A/C. Will new injectors serve me with a better mileage? (Or will injector cleaners actually do anything good?)
Am I to the point where an overhaul of the engine would be in order to get my mileage back to a decent range? I get the same mileage out of my '91 F150 flatbed work truck that has no A/C. The truck has been faithful (so far) - and I value a good running paid-for truck - over a new one with payments - and am willing to put $ into maintenance - because I'm not going to go into $25-$40K debt for a new(ish) truck.
An update the next day... I am 1 month shy of my 1-year service on the rebuilt transmission. I'd noticed problems shifting when at full highway speeds (not downshifting properly when trying to pass someone) - so went ahead and took it in. Seems it's been running 2qts low of transmission fluid for the last year. They topped it off, and it suddenly feels MUCH closer to normal. My MPG will be watched to see if I have significant improvement over the next few tanks.
I would start by putting a bottle of fuel injector cleaner in the gas tank. Dirty injectors will not produce a fine spray of fuel that can burn efficiently. I do this even with my 45 mpg Prius.
If not, I would do a compression test. These and the 5.7’s have a history of valves sticking which can cause ‘misfire’ and obviously poor performance to include horrific fuel consumption.
Lets face it; 300,000 plus miles has been admirable - but, you may want to refresh or replace that rascal.
Geez - it's been a year!
I'd say my MPG has * slightly * improved over time. I ran some seafoam through the fuel system about 15 miles before refilling the tank the other day (I just hit 350k miles last week!) - and will run more through as each tank of gas gets low - so it's more concentrated in the fuel system. I try to drive like a grandpa... feather my accelerations, long coasts to traffic lights I suspect are a stale green-light, etc. I traveled from Dallas to San Antonio twice in the last month - and MPPG did increase for those 2 trips - HOWEVER - they were also at higher speeds (Speed limit on toll road 130 is 85MPH - I try to keep the truck to about 70MPH). Also - from SA back to Dallas - I used ethanol-free gasoline (at 90 octane)... I wish we could get it here in the Dallas MetroMess...
My real concern more than anything, now - is the oil consumption. I'm still having to add a qt per appx. 1000 miles. I keep a gallon jug in the truck with me - especially when I'm making long trips. (Here's screenshots of my mileage records from Fuelly.com )
1 year MPG records last several months records
Originally Posted by ChiefH
Did your fuel economy improve?
If not, I would do a compression test. These and the 5.7’s have a history of valves sticking which can cause ‘misfire’ and obviously poor performance to include horrific fuel consumption.
Lets face it; 300,000 plus miles has been admirable - but, you may want to refresh or replace that rascal.
I hadn't posted lately on my mileage.. the injector cleaner did help a little... What REALLY helped, though - was changing my O2 sensors. They directly affect the fuel trim. I had a code on one this summer - so changed all 4. THAT helped mileage!
(Note - I changed them 2x. I bought some mid-priced ones on RockAuto... and one of those had a bad heater circuit that manifested about 1 month after installing. So ordered GM OE - and installed today to replace the upstream sensors... So far - so good.)
Mileage has tanked recently - what to look at?
