Looking to the Reddit gods for help here. I just did my 100k service on a 2011 Silverado 1500 (5.3 LT) - plugs, coolant flush, transmission fluid/filter, front suspension. Truck drives noticeably better all around, feels like butter accelerating and shifting. BUT. Prior MPG was 16 and now it’s down to 12. I did use NGK Platinum plugs and reused the wires. My only thought is to put ACDelco plugs and wires in but would that make sense?
Air filter is clean. Reputable shop did the trans fluid and alignment. Will clean the MAF shortly. Oil change 3k miles ago.
I’m on a 1500 mile road trip and it’s already not that fuel efficient lol, what would you do?
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Is it possible they replaced synthetic transmission fluid with regular? I’ve been told this can make a difference of 1-2 mpg. That wouldn’t explain a 25% decrease but it may be multiple issues.
Just verified with the invoice that Dexron VI (full synthetic) was used.
Google relearn idle for your trucks PCM/ECC/ECM.
Will do! I’ll let you know how it works
DIYer advice: I’m thinking you disconnected your battery when doing that maintenance and now your vehicle is trying to “relearn” the optimal settings for idle, fuel trim, etc. You might check your mileage again in a few days.
While this is really solid advice, I did not disconnect the battery on this job. It’s been 400 or so miles since the maintenance and it’s staying around that 12 mark.
front suspension
What did you replace, and did you get an alignment after?
The only real change was the NGK plugs. Replace 100k wires. They’ve done their job.
Replaced wires and cleaned MAF, increase of 1.5 mpg now. Still strange but that’s progress.
What would I do if I cared about fuel economy? I would not drive a truck in the first time.
12mpg seems to be the on lower side of reported real mpg by the users. So the first thing you should check if your driving patterns didn’t change. On my WJ, I could do the same trip with 11 and 17 mpg, just changing the driving style. That’s how big V8’s work.
You can test it by trying to make an economy run (slow acceleration, no braking, minimal hills), and see, if you can get close to mpg declared by factory. If you do, the car is fine.
Oh absolutely I agree. But when you do maintenance and the result is a 25% loss in fuel efficiency, there’s something awry. Driving habits have not changed.