Hi guys,

I bought a 04 MDX about a month ago. it has about 98K on it. When I got it the mpg's were around 16 city (right around what I expected), but it has continuously fallen to where it's about 11 now. This is only in a month. If this keeps up in a week I'd lose mileage sitting in my drive way! What could I do to help my mileage. I'm changing the air filter and going to add a fuel cleaner (prob Sea Foam or Redline SI-1 based on another thread I read). What else?

-Vega

 

That rapid fall off would make me check for gas leaks.
Since you have no idea how previous owner used/abused ...
seaform is a good idea {prob my previous thread}.
Besides what you outlined, check for leaks, and establish a new baseline.
If its still bad ... you may have to open her up to see FI,
sparks, valves, etc.

 

I used Octane boost and have already seen a remarkable difference. it's back up to about 15 mpg. I put the octane boost in and added about 3 gallons of gas let that cycle through then filled up about 2 days later. I'm changing the air filter this weekend and going to change all the fluids w/in a month. who knows maybe change the plugs after that. but so far so good

 

oh and no leaks. I would smell that or see puddles wouldn't I? and the gas would rapidly go down.

 

Your poor gas mileage could also be due to a bad Oxygen Sensor. Seeing that it suddenly dropped that would seem to be one of the possible issues. Is your check engine light on? Usually it would be indicated by that but you can definitely confirm by running a diagnostics on the MDX. Also be aware that you probably have 2 different Oxygen Sensors. Ohhh, and replacing the spark plugs wouldn't hurt if you don't know when they were last changed.

 

Check your air pressure in your tires, make sure they are AT LEAST 32PSI COLD!!! Wait overnight and check in the morning! The recommend PSI is 35 COLD!!!

Also have you changed gas stations at all?

 

Only if its a mega leak - Fuel Injectors / hoses / seals can seep out small amounts when under pressure and finding these leaks can be challenge. Snoop {water and soap in spray bottle is best way}.
Buying used w that mileage is always a guess game.
Guess what was done by previous owner and guess whats wrong...

 

All great suggestions. I was planning on the changing the plugs. Checking the PSI when the tires are cold... I live in South Florida, it's never cold lol. I did a diagnostics and never came back weird or broken. No check engine light

 

I have a 2006 MDX with 89,000 miles. I am getting 12.1 MPG WITHOUT AC. I used to get 13.6 with AC. My tire pressure is fine.
ANy ideas?