Friends, I have a 2008 Sport with 56k, bought it a few months ago. Even on a tank of mostly highway driving, I have not breached 30mpg, which is below expectations...a few city tanks have barely exceeded 20mpg.

I have very limited maintenance records, but had the car inspected pre-purchase and there were no obvious issues.
Based on advice from this forum (thanks!), last week I had the plugs replaced (Denso Iridium), and all fluids flushed (trans, coolant, brakes) on the assumption that none of that had been done ever. Also had the throttle body cleaned. I asked my mechanic (honest guy) about a valve adjustment, and he thought the mileage was too low for it to be worthwhile. (Not enough data yet to say if this made a difference in mpg, but so far seems negligible.)

Looking for a second opinion on the valve adjustment - could it yield a significant fuel economy increase? I *assume* that the car was mostly driven in town by the first owner, given the low mileage per year. Does that kind of driving knock the valve clearances out of spec faster?

I have read some stuff here about fuel injector cleaner additives - worth a try?

Any insight would be helpful - thanks so much!

 

@8: You state that you are at 56k mi. Doing a valve adjustment after 30k mi. is not unusual. Have you replaced (or at least inspected) the engine air filter?

 

Thanks so much for the response. Yes, engine air filter was the first thing I changed.

 

I'm not sure you'll get a significant improvement in fuel mileage, but I do our valves every 50k miles and they have been a bit out of spec each time. The maintenance minder on the GD Fit triggers for a valve adjustment somewhere around 60k miles so you aren't way too early.

Changing the spark plugs was probably more important, but it certainly won't hurt to do the valves.

 

Wouldn't hurt to check clearances. I have 178k and don't think mine have ever been adjusted. On the list of things to do.

That mileage is crazy low. I'd definitely consider running some injector cleaner since that fit was hardly driven. Id also clean the sensors and take a look at the 02 sensor to see if it's fouled up. Any CEL codes?

I'd also check your brakes to make sure none of them are dragging. Double check tire pressure as well. You should get more than 30mpg highway. My fit has 3x the mileage and I get 30mpg in stop and go city commute.

 

If you have an infrared thermometer, go for a ride and then check the temperature of each wheel right around the hub. If one is noticeably hotter than the others, that may point towards a stuck/dragging pad like Koro suggested. If you have no check engine lights and aren't using the worst gas on the planet, I think that's a good one to check, as your mileage is very abnormal.

 

Thanks all! I will run a bottle of Techron, and see if I can get my hands on a temp gun - that's a great simple way to check for a dragging pad. Thanks!

 

Another way to check for a sticking calliper is to touch the wheel after driving. It should be hot but not burning hot. Compare both sides to see if on is much hotter.

 

Thanks all for your suggestions!
I had the brakes checked...one rotor is a little warped but no stuck calipers or dragging. I also ran a bottle of Techron and double-checked tire pressure. No change.

Last week we had super mild weather here in Chicago (60s), and all of a sudden I got 30mpg on a tank of mixed city and freeway.
I'm wondering about the O2 sensor, and the thermostat.
Are the O2 sensors on the Fit worth cleaning, or is it better to just have it (them?) replaced?
I know that a thermostat stuck open would cause bad highway mileage due to the engine running too cold. My "cold" light doesn't come on during freeway driving, and of course the cluster doesn't have a temp gauge. Is this a possible culprit?

Thanks!!

 

Being in Chicago, you may also be battling winter blend gasoline that hurts economy.

For the temp, you can get an OBD2 dongle and run an app like torque to monitor the coolant temp, but I'm betting it's fine. These cars run pretty cold as it is compared to other modern stuff.

This may sound crazy, but have you tried the "Italian" tune-up? That's where you run it hard and get some heat in it to "clean" it out. With how low of mileage it has I'm wondering if it's been babied it's whole life and only seen short drives. That's not necessarily a good thing. The harder I run ours, the better it runs. With nearly 200k miles it feels like it's almost broken in and that's with a high percent of wide open throttle driving.

Which leads me to another possibility....a partially clogged catalytic converter. They also work best with longer drives and more heat. If that car had lots of 4 mile long drives or something, the cat may be less than perfect. But, back to the "Italian" tune-up idea...maybe that would also help the cat.

If it were mine, before buying any more parts, I'd get it out on the highway and run it hard. Maybe with a bottle of Techron in the tank. Try to run through a half tank of fuel or better running it as hard as you can legally.

 

Not a bad thought - I'll try to run it high in the RPMs when possible!
Agreed that the thermostat seems like a long shot.
What about the O2 sensor though - is that worth cleaning or just replacing?

 

Anything is possible, but our O2 sensors are still working at near 200k miles.

I've never tried cleaning O2 sensors, so I don't have a lot of experience with that. As I'm typing this, I'm waiting for my RockAuto order that includes a new primary O2 sensor. Sensor itself is still fine, but I shattered the connector when I, very stupidly, used my battery powered impact to remove the sensor from the exhaust manifold. Came out perfect but the connector shattered into a hundred tiny pieces on the first thing it touched.

I could buy a new connector and put it on the old sensor, but I figured with near 200k miles, this was a sign to just order a new one. $110 or so lesson since these sensors are not cheap.

 

I recently got a GD3 Sport manual at 138k miles that was only getting 19-20 mpg. It had an aftermarket oil filter, K&N air filter on backwards, no valve adjustment, terrible Aspen tires on OEM rims and Bosch spark plugs with original coils. At 140,800 miles now, since then I've put in Amsoil 5W-20 with OEM filter, generic air filter and NGK Iridium IX plugs installed with a Techron bottle fill that led to 22-23 mpg.

Added GE8 wheels with Toyo Extensa HP II tires OEM size 185/55R16 and Progress RSB, didn't see a change.

Next, the valve adjustment with all seals replaced with OEM; all the exhaust valves were TIGHT under 0.005 in. Led to 24-25 mpg.

Lastly, replaced the ignition coils with OEM Hitachi ones and cleaned out the EGR valve. Now consistently getting 26ish mpg. That's about right for overall city. This is 70%/30% city/highway miles. I have not done any long highway driving to find out that mileage yet though I'm confident it's 30+ at this point.

This is all recorded through the Fuelio app and mostly on Costco 87 octane.

 

Update: On @GAFIT 's advice, I drove it hard one evening on the freeway. The next time I fueled it, it took a LOT more gas than I was expecting, like 3 gallons more, and that tank was around ~18mpg. Today I filled at roughly the 30% mark...this tank was a mix of highway and city, including one really ugly day with lots of idling in cold weather. 31.7mpg, a record for this car. So, was some crap in the fuel system?? So bizarre! But it seems to have worked!!?

 

It's not anything in the fuel system, it was carbon in the combustion chambers, carbon on the fuel injectors, a partially clogged converter, partially clogged oxygen sensors, blocked EGR, or something else that needed heat to clear out.

Cars do not do well with being babied all the time. Heat is part of the key to them staying clean internally.

Glad to hear it's running better!

 

I didn't even think about that. I bet a new, high flow cat would really help.

 

Really appreciate the advice, @GAFIT ! Thank you!

 

I love it when you talk like that.

Let's drive these cars, gentlemen. Life is short.

 

I still remember when I was a kid my grandmother had a 1978 Olds Cutlass Supreme with the Rocket 350. It was too much power for her so she would ask my Dad to take it out once in a while to "blow it out." I always enjoyed those rides! My Dad and I were always amused that you could watch the fuel gauge go down while it was at WOT.

Shows that even my grandmother appreciated the idea of the "Italian tune-up."

 

When I first got my GD, I took it up in the canyons and wrung it out — shifting at redline, diving into the turns, smoke coming off the rotors at the end of the run. I was laughing my head off it was so much fun.