Many of these chain stores (NTB, AAMCO, Iffy Lube, etc.) have under-trained or untrained people doing the oil changes.
It’s the bottom rung of the ladder.
You’re lucky they poured the oil into the right hole.
Better to find a good independent shop.
I don’t think 5w-30 vs 5w-20 would make more than 1 MPG difference.
Longmatch:
Concerning your question about whether the use of 5w30, instead of 5w20 caused your 4-mpg mileage drop, I doubt it. The few automotive and oil company reports I’ve read about using lighter oils show an mpg benefit in the 1/4 mpg range.
I am very interrested in what you see after you change out the plugs. I am having a similar experience with my 2006 Honda Accord 4 cyl. I too track my mileage every tank. At about 50K miles I started to see about a 10-15% drop in MPG. I have gone from a consistent 30-31 in every day driving (country roads, limited short city type trips) down to 26ish. I used to be able to pull a good 34-35 highway, now 30ish.
I just cleaned my MAF sensor, which was very easy to do. I also cleaned my throttle body, also fairly easy to do. You might want to try this as well. I just filled up yesterday so I will see what happens over the next tankful to see if these were the culprits. Plugs are next on my plan if there in no change.
I’ve recently seen the same type of drop on my 2006 Pilot. 4 yrs or consistent 20-21 MPG, then suddenly just under 18 the last few months. Changed out air filter, have not done plugs yet. ATF is a little overfilled after my last change, so maybe issues around the shift timing being effected? I know it’s an old thread, just hoping the original poster might have found a cause.
Exact same thing happened to me: 2006 Pilot, 85k, no problems. Got new tires, MPG dropped from 19-20 to 15! Thought it was the tires - replaced them - no change! Plugs next I guess. Any followup would be very helpful! Seems to be a trend…
I had my mechanic change the plugs and adjust the valves in my 2004 Pilot (140,000 w/ original tranny) and had no change in mileage, although it starts a little easier and runs smoother. I changed tires and with proper inflation I immediately went from about 19.5 to 17 mpg. If this isn’t your issue, my guess is a dirty intake or injectors.
New tires often have have higher rolling resistance, then the treads wear down, the rubber hardens, reducing squirming.