Ever since I got my RDX (2007 base model, used) in July of this year I've been getting an average of 18-19mpg with combined city/highway driving. If I did mostly city, I'd get about 17mpg. All of a sudden, starting last week, my last 2 fill ups have been getting me 15mpg MAX. I filled up at 2 different stations (Exxon and Shell), but they are stations that I normally fill up at. The only thing I did different, that I can think of, is that I didn't get a full tank. About 8.5gal (~half tank) each time. Other than that my driving has been normal, no tire pressure warnings, nothing new in the engine, I just had my oil/tranny/transfer fluid changed by Acura last month. Engine is stock other than a K&N panel filter. The first of these two times I filled up I thought I just got a bad tank of gas (because that's happened to be me before), but my second fill up got me the same horrible gas mileage as the first. What makes it worse is that the price of premium just went up to well over $3 here and I'm only netting 14-15mpg.

Any ideas? Things to check on? I'm going to check my air filter today just to make sure there's not some crazy blockage.

 

air filter too dirty?

 

^^ That and dirty fuel injectors were my first suspects. I'm going to check/clean my air filter today. What do you guys recommend for injector cleaning on the RDX? I used to use SeaFoam on my Accord. Poured a little bit into the empty gas tank before filling up.

 

Yeah Seafoam the gas tank + engine oil crank case....i do this on my 05 TL...

again you have a turbo in that rdx so PLEASE CHECK WITH A TURBO person if you can seafoam the engine oil case + intake mani....

also pull one of the spark plugs out and see if they are ok

tire air pressure should be around 34-36 (i have seen best gas mileage at those pressures)....

also take that foot off the gas, will ya ?

hope that helps....

 

Could the gas be causing the problem? I always notice a drop in mpgs in the late fall and winter months because they use 10% ethanol in NM. It usually goes back up to normal in spring/summer.

Might be a good time to do the Hondata reflash! I’ve notice my overall gas mileage average improved from about 19.2 to about 20.6 with about 60 hwy/40 city (hwy speed about 70 mph in city and 80 mph on interstate).

Do you have a short commute and the weather been extremely cold? Have checked out your thermostat? A cooler running engine will burn more fuel. Maybe the tires could be out of alignment adding more rolling resistance? Do you have snow tires on? Any extra junk in your trunk? Do you hit the turbo pretty hard?

 

ive always "wondered" about this - whether it's true or not. anecdotally, ive heard a few people say that winter blend gasoline will give you less mpg vs a "summer" blend. we have winters in the 10-30F here in toronto (though thankfully we missed the blizzard completely and it will be 40-50F tomorrow till new year's day) so i wonder if the colder the less "efficient" winter blend?

nonetheless, i always gas up with shell (zero ethanol) 91. and it's always advertised here as such (zero ethanol, hence i stick with shell). my summer vs winter mileage is ~5-10% diff. consistently

 

I thought it was really odd since I've been driving the same routes and with the same style. I actually got better gas mileage when I drove more spiritedly (is that a word?). But with this drop in MPG I've been really conservative and it's STILL bad!


Short commute - yes.
Extremely cold weather - yes.
Tires - rotated (and I'm assuming aligned) at my last service a month ago.
Snow tires - no.
Extra junk - not since I was getting "normal" gas mileage.
Turbo - not really. When I pass on the highway I usually downshift, so boost doesn't climb too high. I don't really hit it too hard from a stand still either, and I've been cautious of the turbo since this MPG issue started.

I think I'll try letting the car warm up more before I start driving. I normally just start it up and go after about 30 seconds in the morning (1st start). I keep it under 3k RPMs (through the neighborhood) until it warms up (2 tick marks on the temp gauge).

Does anyone know about Seafoam on the turbo engine? I don't see how it could affect the engine differently than an NA engine...but just to be safe before I foul things up ?

 

Winter gas + RDX = shit MPG. mine also dropped this last week. avg 13. 100 miles @ 1/2 tank. nothing out of the ordinary, at least for me. Stock filter however. I change my K&N out for the winter back to stock.

 

^^ Wow that sucks . Is there a reason why you change your air filter back to stock for winter?

 

Winter blend gas, bad weather, and many other factors affect gas mileage. However the number one factor that has happened to me is a pump jockey fucking up and putting regular gas in the RDX (or TL) when I specifically asked for premium (92 octane). This was occurring once every three months or so. I wouldn’t notice until when I got the receipt or later when the car was underpowered and getting 15mpg. I finally started getting out of the car every time I filled up so I could watch the attendant press the 92 octane button (no self-service gas in Oregon).
It is possible that you got some lower octane gas and filling only half the tank still did not remedy the situation. Try an octane booster.

 

New England, lots of skiing/mountain driving, sand, salt all the time, added piece of mind and better protection with the stock, but most of all, not worried about cleaning. Its best to clean the K&N at the most @ 15k intervals, altho they claim otherwise, where i live/drive, thing is filthy at 10-15k. Would not want to see it @ 25k plus. I cleaned a friends @ 25k in a civic, could not restore it thing was totally shot, had to get a new one. When i first installed my K&N in the RDX, i had never used the filter in any previous vehicle, so i would pop the air box every couple K to check the integrity of it....my experience and visual inspections dictate the low mileage cleaning. it just gets too dirty too quick for me.

id love to know how many posters here really get the MPG they 'claim'. How many miles do you get to one tank? during the winter, im filling up around 260, maybe 270, sometimes even 250 miles. Since ownership, including the 07 and 08, i hover around 18 no matter how much i drive, city or highway. Ill see great highway MPG and then a little bit of city sprinkled in the same tank kills it. Regardless of what the computer says, I clock in under 300 miles per tank. Period. K&N helps give it a smudge bump, but even still. 300 miles to tank is a prayer. thus, ive always considered the RDX to be an under 20 MPG vehicle; i dont care tho, the driving fun more than fills in for the hit at the pump, plus its a turbo...u know what ur getting into before you buy the car...its just surprising that its been so consistently low i guess lol. 100 miles @ 1/2 tank LOL. o well, no idea why this thing didnt get some powerplant, programming & tranny revision like the MDX to squeak out 1 or 2 more MPG's....its been untouched since it came out...just not justifiable when other vehicles with higher output or more cylinders get the same.

 

I guess the variable-flow turbo makes it nearly impossible to stay out of boost and that probably has something to do with the overall MPG of the car. I agree, it's a fun car to drive and I'll take 18mpg for that. 14-15 is just killer though.

Mr Marco, it's almost the exact opposite here. I thought full service pumps were a thing of the past, since I had only seen them on TV since I was a kid. There was one station in a small town I drove through that had a full service pump and the guy actually got upset because I tried to get out of my car and pump my own gas. I had to pull up to another pump to do it myself. So long story short, unless they put the wrong gas in the reservoir, it should be 93 octane (from both Exxon and Shell).

 

I thought mine was bad, I am getting about 20 average, mostly highway. I put about 2500 miles a month on the Rdx and it has been consistent around 20 or 21 over a 1000 mile trip. I drive 80 about everywhere.

 

I made a 360mi round trip today and avg 20-21mpg on the highway. Speed was about 70-80mph almost the whole time. I think it's my air filter (still haven't taken it out to clean it) because I noticed this morning, even after I let the car fully warm up before pulling out of the driveway, that when I sit at a light, I can watch the MPGs tick down .1mpg at a time. In the course of 1 red light, I lost about .4mpg =O

 

10% ethanol gas makes a noticable difference, up to 20% less, in my 2009 RDX, especially in the winter. The car travels <10 miles one way each commute, and just does not get warm unless there is heavy traffic, which also decreases the milage.

So I try to use NON ethanol whenever possible, both for better milage and because of my concerns about the other ethanol problems (water and fuel separation).

Of course, NON ethanol costs more per gallon here in Utah. Not sure if the improved milage (over E10) completely compensates for the higher cost.

 

Hmm...I'll have to pay more attention next time I fill up, but I don't remember seeing any notice/warning about ethanol in the gas at the pumps I usually fill up at.

I cleaned my K&N filter yesterday and so far my gas mileage seems back to normal. Although I got 22mpg max driving 180mi on the highway at about 70-80mph. I remember getting 24mpg a few months ago on a different city-to-city trip...all highway.

 

non-ethanol stations are few and far between, needle in a haystack.

Ethanol is less efficient so no surprises there. I just filled up @ 210 miles on my most recent tank. Ha, whatev

 

Mine has also dropped a bit, probably due to cold weather and winter gas. Went from about 22 mpg to 19 avg. Also, you said you have a short commute. Short trips will absolutely kill your mpg. I used to have that problem in my old TSX because of a 2.5 mile commute. Now I either work from home or have a 90 mile commute to the office.

 

Could also be an O2 sensor, but you'd have a CEL if that were the case. Just putting it out there in case the light pops up.

 

Thanks guys. So far no CEL. Although I did get one a couple of weeks ago...it came on with my VSA and Traction Control lights. I turned off the car and started it back up and the VSA and TC lights were gone...then the CEL went away after 3 trips (shut off, start up, drive...). Which is what's supposed to happen if the problem is no longer present. My MPG was normal immediately following that as well.

90 mile commute to the office?! That's not a commute...that's a trip! I think my commute is about 10 miles. I was making shorter trips because it was the holiday break and my family lives in the same neighborhood. Walking would've saved me MPGs...haha.

I also checked the pump when I filled up this morning...it says it may contain up to 10% ethanol...so I'm assuming it does. Is there a reason why it's being added to gas now? Burns cleaner?

 

I get this every once in a while I dont have a code reader yet and have tried to narrow down why it happeneds! It seems to only occur when the weather is damp/wet... very frustrating

 

Ethanol has less energy than gasoline. But when using E10 (10% ethanol) you should see approx. 1-2% lower MPG.

 

So let me see if I get this correctly. We put the ethanol in our gas to help:
1. Reduce our dependence on foreign fossil fuels.
2. Save money.
3. Better the environment.

But:

1. We currently use more foreign fossil fuels than ever before.
2. Ethanol is more expensive.
3. Ethanol is hurting the environment because it uses more fossil fuels than it replaces.

Oh ya, it is harmful to your engine and your gas mileage decreases. Apparently someone is making a lot of money off ethanol.

 

I hit a curve (one of those curved "yield" lanes at a 90deg intersection) pretty hard...and I think there was a bump involved too. I thought maybe it had jarred one of the battery cables for a bit causing the lights to come on, but I checked and the cables are tight. Car has been fine ever since, other than my MPG situation. That seems to have gone away now as well. All I did was put a can of Seafoam in the gas tank and cleaned my K&N filter. The filter didn't look too dirty...but I guess it was.

 

Yeah, that pretty much sums it up. I think the "dream" of using ethanol was that the emissions were less harmful, too. But so was propane, and we all know how well that worked!

My Porsche OM says to not use ethanol blends. Doesn't say why. Even though the octane rating is sufficient (even better sometimes!).

Oh, and ethanol is often used in colder climates, as a gas-line antifreeze.

 

So what are Porsche owners supposed to do now that it's so difficult to find gas with no ethanol?

 

^ Ha....I was wondering the same thing. Almost every gas station now has 10% ethanol. I really wish they didn't, but we have pretty much no choice now.

Yeah, my commute kind of sucks, but luckily I don't have to do it every day. I moved to NY last spring to be with my bf. I used to have a 2.5 mile commute!