New plugs, mileage dropping?

I had my plugs replaced on my 2011 recently and I noticed my mileage is dropping. The old plugs were pretty bunked up so I would think the mileage would improve if anything. Before the swap I was averaging 19.9 mpg and now it’s dropped to 19.6. Could be unrelated but figured I’d ask. I was thinking maybe the mechanic put the plugs in for the newer 5th gens. I know they use a different plug. Thanks for any advice.

 

I can drop .3 MPG's if I sit still in traffic for more than 30 seconds.

 

.3 mpg loss, there are thousands of day to day factors that can produce a .3mpg loss. Test it over a few thousand miles and report back.

 

If you’re going off of the computer and especially if you’re using “after refuel” then that’s pretty much within margin of error

 

What type of a mileage span are you using in regards to your estimates?

 

I average between 14 and 15 mpg, so I'd say you're doing pretty well.

 

If you're worried about the new spark plugs you can stop worrying.

 

Have you checked your brakes? Had a stuck caliper that was causing the marginal fuel increase. I was getting a scraping / rubbing noise when turning hard left.

What's weird was there was no loss of braking performance.

 

That .3 loss is because you didnt take a dump before driving and the added mass of the feces within you is causing your engine to work harder.

 

Thanks for all the feedback. My brakes are fine and I was averaging almost 20 mpg for thousands of miles before I got my plugs changed. Then immediately after the new plugs my average dropped to 19.6. I still think it’s very good mileage I was just concerned because of the timing of it all.

 

Because of all modern vehicles being run by small computers (ECM), it had probably adjusted for increase in gap, timing, etc. over time as the plugs wore. Now you've introduced a new component, probably with smaller gap, and a hotter spark, and the ECM says WTF? Whenever I change plugs or coils I disconnect the battery for about 30 minutes to clear any old information. The ECM should start at a baseline and adjust everything based on the new plugs. Give it a shot.

 

+1. OP has an SR5, not TuRD Off Road, so it doesn't handle feces as well.

 

did you make sure all plug gaps were consistent? Some can get banged around close up some

 

this makes sense. But wouldn’t the computer adjust to the new plugs eventually without having to disconnect the battery?

 

You would think so. I just do it every time I change plugs and have had good results.

 

i wish i got 19+ miles per gallon. I just changed my plugs and went from 14 to 15 and i celebrated.

 

yeah I am pretty happy with the mileage I get. But I live in Florida where it’s very flat and I pretty much drive it like a grandma. I also don’t have a lot of extra weight added to it.

 

Replacing my spark plugs among other things for my 100k. Would be nice to get better MPG.

 

I wouldn't get your hopes up.