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My driving has been consistent in a 2014 and 2015 MDX SH-AWD Tech. On November 1 I retired so most of it is around town these days, which accounts for much of the falling MPG. However that can't count for all the fall because we did a lot of around town driving before, and on the way home from work every day there was much stop and go along the same routes I drive in town now - and now I drive at times when traffic is smoother. Even a long freeway trip to take the dogs to be groomed ended up 3 or 4 MPG lower than that same trip is usually. Any ideas where to start? The cars behavior is the same and there are no warning lights or DTC's. Dealer maintains the car when the codes come up to service it. Here are the mileage logs. Seems like around April 1 is when the trend began, and June 1 is when it began to fall the most. Some of those higher MPG's in May were also mostly freeway and instead of being up around 23 - 24 MPG they were below 20. The last tank at 14.5 driving was no different than some of the freeway and town driving last year.
Last edited by merlin the wrench; 08-04-2019 at 09:23 AM.
My 11 MDX has combined 17-18 mpg during my daily commute of 60/40 hwy/city; but, can get up to 22-24 mpg depending on how long the why runs with minimal shifting. I can see 14-15 mpg with majority city driving. Geting 14-16 mpg is my norm mpg when I visit larger cities than ABQ with my 3.7L+6AT.
I would only be concerned it my hwy mpgs also dropped my the same amount. It sounds normal for me with a +2 ton awd SUV in city driving. That is why I decided to go for the MDX sport hybrid instead of the 3.5L version. So far, I'm at 25.3 mpg combined with the sport hybrid compared to the same city driving I was getting 17-18 mpg in my 11 MDX.
I did some calculation for you. From Jan 9th to Aug 2nd, for almost 7months, 176 days, you drove only 2,659 miles. That's average daily of 15.1 miles. Avaerage MPG for that period is 16.67 miles. Are you complaining that for being poor mileage?
I drove more miles than you did, about 5,500 miles during the same period, averaged about18-19mpg, roughly 50% of freeway and 50% city streets. Don't know where in No Cal you're but here in Vegas, most city streets are 45mph zone, only the first and last mile is 25mph or lower speed zone, I also try to avoid rush hour traffic. My old SUV that I replaced with this MDX was about the same weight, but only averaged 13-14 mpg, big improvement. I wouldn't worry about losing MPG, in your case.
There is literally dozens of variables that effect MPG of new cars.
I personally would start with new plugs, new air filter and clean the MAF. Even a small amount of dirt can cause bad readings.
Thanks all. What threw me is I thought it might be caused by just more city driving but a freeway trip at a steady 65 -70 mph of 110 miles with only a small portion in the city fell from a normal for that trip of 24 -25 mpg to 22 mpg. City driving has fallen 1 - 2 mpg too. I'll check the air filter since I have been trusting the dealer to do it.
well, pulled open the air filter housing tonight thinking it would be a waste of time and that it would be a clean white filter since the dealers don't miss an opportunity to sell something when the car is in the shop for a service - which it was 1750 miles ago in April. I paid for a full check up too when I bought it from another dealer which was 13800 miles ago. The side facing the incoming air is solid black and debris. Will replace it tomorrow. Not a happy camper with the dealer or Acura since I have never seen an air filter get this dirty even in 20,000 miles. I suspect it is the one that came with the car - it has 40,700 on it - all my driving is street and freeway. So much for the CPO service before buying it too - we caught some items there that were checked off on that list that were not done - that was Acura Leasing or their stead who did that service, and the dealer who sold it looked over it. My dealer caught the items they missed. My local dealer gives you these peace of mind 37 items we checked print outs when they service the car for anything. Apparently checking the air filter is not one of them. Stupid, I can see where this is headed, which is back to doing all my own servicing.
Last edited by merlin the wrench; 08-06-2019 at 11:06 PM.
There is literally dozens of variables that effect MPG of new cars.
I personally would start with new plugs, new air filter and clean the MAF. Even a small amount of dirt can cause bad readings.
I agree on clean the MAF. If you have a scan tool that reads fuel trims, see if they are positive. That indicates the the PCM is adding extra fuel.
Being in Kalifornia, you may be the victim of CARB screwing with new fuel formulations.
California All counties implement a version of the California Reformulated Gasoline Program, not just those listed here as Clean Air Act-required areas. Standards differ from federal RFG requirements, and compliance periods vary by air basin. Please refer to the California Air Resources Board website for additional details: https://www.arb.ca.gov/fuels/fuels.htm
did about a 1/3 tank the last few days. Just with the change being about 1/2 of that my mileage has come back up to what I would consider in the normal range. Will keep watching it.
I see you found a dirty filter, which may be part of the problem.
But here something to think about:
The engine is direct injection, and some DI gasoline engines are prone to excessive carbon on the intake valves. This is caused by excessive oil in the blowby that the PCV feeds back into the engine, and the excessive oil in the blowby is a side effect of dirty air filters and oil breakdown.
Unfortunately, the old fashioned way of running some cleaner through the fuel does not touch the crap on the valves, but will clean some dirty injectors.
Try a couple of tanks of gas with Berryman's B12 or Gumout cleaner to clean the injectors and see if it gets better. If not, consider getting someone to run a bore scope down the intake runners to look at the intake valves.
Also, brand of gas matters. Stick to something that is a Top Tier.
Last, you mentioned that your driving is mostly around town these days. Are you aware that that kind of driving is harder on the oil than highway? A bunch of short trips where the engine never truly gets up to running temperatures leads to the oil breaking down much faster than if it sees a lot of highway.
around town usually means surface streets, which can be 10 miles in each direction added to a 15 mile away destination. These aren't kids to school and back trips. The consequences of a dirty filter did come to mind. My CJ7 would build up carbon on the intakes - when a chunk broke off it could damage a spark plug or rattle like hell until it exited. About 1992 or so I took chunks of that carbon (more like coke) and put pieces in almost every known carbon solvent that was recommended for cars. That included water, Water and soap, Ammonia, ATF, Marvel Mystery Oil, Berryman's, WD40, Gumout, GM Top Cyl cleaner, Acetone, MEK, and a couple more. Each one was in a glass jar soaking. Berryman's took about 3 or 4 days to soften the top layer but not the core. The others didn't do much. A couple softened the top layer after a couple weeks. The GM Top Cyl cleaner turned the carbon to like toothpaste in a few hours. When Acura had carbon problems with the Legends back in the mid 1990's that is also the product they chose to dissolve the carbon. The draw back is that it smokes and smells terrible when using it and if you are in a place where you have neighbors they will complain. I found that the best way to use it was to go out in the country on a rainy windy night, put it in as specified. Listen to music or read for a couple hours then blow it out, then go home and change the oil. Alternatively get up at 1:30 am on a rainy windy night, run it into the engine, go watch a movie and when it was over go blow it out. The rain and wind carry the smoke away without pissing off the neighbors. It looks like a thick fog behind you when it burns off. I bought an extended warranty until 2022, and 100,000 miles so if there is a problem Acura is on the hook. Also this thread documents that they didn't change the filter when we bought the CPO like the check list says. The dealer just did a multi-point inspection 1750 miles ago when they changed the oil so they are really on the hook for this if there is secondary damage. They were just in the cabin filter to look around on that oil change because there were stains on things in the glove box after a long trip to SoCal and we don't know where the stains came from. They did not note it was filthy. I doubt that is only 1750 miles driving on that filter.
Last edited by merlin the wrench; 08-09-2019 at 08:36 PM.
08-04-2019, 09:19 AM
