97 Civic HX MPG not up to snuff
 

Hello the camp...new member to your forums needing some assistance.

We recently helped my daughter buy a 97 HX specifically for the fuel mileage aspects. She drives the car back and fourth to school which is about 18 miles one way most of which is highway. After driving it for several tanks at various speeds....first tank 75 ...then 70...then 65...then 60 (Which is hard to do when the speed limit is 75 on this TX Hwy...bless her heart she was a trooper to test for the sweet spot on mileage).

I have read you need to keep the RPM at or below 2500 rpm to reap the benefit of the HX's fuel economy which we have done repeatedly.

The problem is that at any of those speeds the best we have done is 33 mpg.

There is no CEL and the car runs and drives just fine. I have replaced the air filter (which was a mess) spark plugs, cap/rotor and just put new Michelin tires on it (not just for economy...it needed tires anyway) as well as an alignment and so far nothing has had an impact...still 30ish mpg.

I am going to try cleaning out the EGR valve next and check the timing as these have been suggestions.

Anybody have some insight as to why this HX is only getting 30-33 MPG with no check engine light? She is not using any fancy driving techniques but she is also not a lead foot so I really don't get it. This car I would think should be getting into the high 30's low 40's easily....:confused:

First thing that comes to mind is thermostat. Could be stuck open or even missing(happened to me). Also fuel filter. Just for giggles, I'd have the car scanned for codes. Could have the CEL bulb removed(also happened to me).

Best of luck and great choice in vehicles!

Check for proper NGK plugs and good plug wires. Good idea to change the cap and rotor, too. You could have a rear brake dragging - jack up the rear end and see if the wheels turn without the e-brake on. These cars run a lot better after a valve lash adjustment. If it has not been completed anytime recently, or within the last 90K miles, replace the timing belt just to be safe. Make sure your tires are in good shape and inflate them to the sidewall max. Of course, Low Rolling Resistance (LRR) tires are best for mileage.


When I bought my VX, I was getting about 44 mpg. After a valve lash adjustment, tune-up, better tires, and rear brake adjustment, mileage soared into the low 60s.


One last thought - Honda are more affected by winter blend gas than anything else I've driven. My Accord dropped from 31-33 mpg to 27-29 mpg, with the only change being our stations' switch to winter blend. My other Hondas (VX, del Sols, '99 Si, '05 Si, '08 Si, '10 FIt) have had similar drops on winter blend gas.

Oh wow! I had a Civic VX hatchback a long time ago and loved it. I never calculated the MPG back then though. I do remember it would do 114MPH in 3rd gear though! :)

I also had a Civic HX CVT at one time. It was a black coupe. That was a cool car but I never calculated MPG on it either.

You mentioned the EGR, and that's the first place my mind goes on any lean-burn Honda (HX, VX or 1st-gen Insight). They rely heavily on, and are super-sensitive to, the EGR functioning properly. I hope you will report back here!

Well, another thought. Not sure if you're still seeking advice, but I'll throw it out there. US emissions regs forced Honda to really severely narrow down the conditions under which it will utilize lean-burn. It could be that the commute offers little to no opportunity for lean burn to be activated.

no stock VX can do 113mph
 

There is no VX that can do 113mph in any gear let alone third gear.:eek:
You must have had an SI not a VX.:coolsmiley:

I agree with the winter blend and timing belt as a possibility.

I know lean burn will not engage unless I am at 65 mph or less under very light load with a rock steady foot on the pedal. If she is the type to slightly accelerate than decelerate a lot (which my mom, wife and sons do) then it wont go into lean burn.

When lean burn is on my mpg increases by 30 mpg.