Hey guys. New here. Have been using your forum as a guest since I got my car. I have an 09 fit sport, 5spd auto. I have owned it since new. No mods. It has been an awesome little car. One of my favorites. I have read many posts on here and have looked at them on my car and none have fixed it. My problem is that over the past month or 2, my mpg has gone way down. I normally average 33-34 mpg combined. Last night I pulled my mpg and it was down to 28. Half city and half highway driving. I'm not a lead foot any more. Changing spark plugs this weekend. Oil is new, tranny fluid is new. Air filter new. No exhaust leaks. No misfires, no CEL. Valves are spot on for clearance. I have noticed over the past month that when engine is cold it sounds like a diesel when accelerating. If in park or neutral, no sound. Took it to Honda and they said nothing wrong. Typical. I pulled the oil pan. No shavings in oil. Could move the rods side to side ever so slightly. Nothing major. Plugs are a little white. They are about 70k. No misfires. No smoke in exhaust. I'm really scratching my head. Pretty mechanically inclined. Rebuilt 74 celica with 18rg engine. Any suggestions?

 

My fuel economy drops every Dec-Feb. I suspect that in colder climates, oil companies can finally unload all the shorter molecules that would turn to vapor in warmer weather. Those shorter molecules do not offer as much power (per gallon) as longer molecules.

Snow tires have also been a drag. I've seen a drop from 34 mpg to more like 28. Always bounces back around late February.

 

And the diesel sound? I've never had that much drop in prior winters. It's got me wondering if the 2 are connected. Tires are brand new 34 nitrogen turanza from Costco.

 

Sounds like you know what you're doing and you've checked pretty much everything already.

I also see a similar drop in winter anywhere from 10-20%.
From colder temperatures there's more friction and takes longer to warm everything up. Colder air is denser, so more air drag too.
You've got winter-gas probably, with more ethanol, so less energy. Another one is having the blower on windshield setting which automatically engages the A/C in the Fit.
Then new tires also drop mileage at first. Nitrogen doesn't make any difference, air has almost 80% nitrogen. I read somewhere that places like Costco hardly reach 90% nitrogen at best. Only pro equipment for racing reaches 98%-99%, and even then it won't improve mileage.


Mine always sounds rough after cold start when it's around or below freezing, but only for a little bit. I always wait about 1 min idling in neutral when this happens and when I drive it sounds fine.
Do you drive right away?
How long does the loud engine last?
What oil do you use, the 0w20 synthetic?

 

I let it sit for at least a minute. Sometimes 5 minutes. I use the 5w20 blend. It lasts for about 15-20 minutes. It goes away once the engine is really warm. Wondering if it's the wrist pins or slap. It's very annoying. Just started doing this when it got a lot colder out.

 

You can see the MPG on my 2011 Sport AT jumps around a lot and that is the reason I have the red line which is the average MPG for the last 15 fill ups.

You can see how loose spark plugs hurt my MPG in late 2013 / early 2014.

The overall trend is going lower because I do less and less highway driving. 85% local anymore.

 

Recently, on a whim I got some valve cleaners from LiquiMoly, and after filling them in the tank got an immediate improvement in my mpg. Your mileage may vary, but I saw this improvement after its use.

 

Larry... thanks...I had no idea

https://itisscience.wordpress.com/20...-a-difference/

 

I dont have an answer but I am currently having the same issue in my 09 fit MT as well. No CEL but engine makes more noise when under load and idle seems a bit rougher with more vibration, especially when cold.

MPG dropped from 35+ to around 30 over the thanksgiving week in one tank.
I have new plugs, fresh sythetic 0w20, filters, trans fluid, 35psi in tires etc....

 

It would be interesting to know if owners of other small cars (non-FIT) are experiencing lower gas mileage this time of year. I suspect many are (those that pay attention would know).

Another aspect of our MPG variability is engine / tank / vehicle size. I have a pickup truck (4.6L V8), the FIT (~1.5L I4), and several motorcycles (650cc V-Twin and Single Cylinder), and in all cases I fill up to the top when I need gas and I track it in spreadsheets.

I see that the truck is the most consistent in MPG readings (95% of time between 12 & 18 MPG / 6 MPG delta), the FIT has more variability (96% of the time between 25 & 38 MPG / 13 MPG delta), and both cycles MPG can swing by 20 MPG (not enough data on V-Strom). This is not due to blends of gasoline (ride when it's above 45 deg F and no ice on the macadam or forest roads but a lot less in the winter - Pennsylvania) but small variations in fill up technique, driving style (highway / local / dirt roads on a cycle), and weather. These all seem to impact smaller / lighter vehicles more significantly.

When put into perspective, it's just the nature of the beast and not a worrisome mechanical issue in our FITs.

 

The only reason I'm worried about it is because mine sounds like a diesel now when it's under acceleration when engine is cold. Even when the temp light goes out it still sounds like it for a little while. It happened Within a month or 2. And my mpg has never dropped into the 20's before in the winter.

 

Mine sounds like that too. Sometimes I wonder if the sound is coming from an accessory to the engine, and therefore, not bearings / valves giving up the ghost.

When I start it up, pop the hood, I can hear chattering sound that almost seems to be an air-actuated valve. I might be way off base with this hunch but just wanted to mention it.

Has anyone ever talked to a dealer about it?

 

I had mine there. They said they had 2 techs going over it and there is nothing wrong. LOL The usual line of bs.

 

Well if this is any comfort, I have a 2011 with 61K miles on it and it has made that winter-time noise (noticed it) for last 3 yrs with no noticeable negative effects.

Another theory of mine is if it is valve train noise then it means that there is excessive gap, when engine is cold, between the valve stem and rocker arm. As the engine heats up, the metal parts expand and reduce those gaps and the engine gets quieter.

This summer, I'm going to check my valve clearances. Lose / noisy valves will hurt performance but too tight / too quiet valves are probably getting burned. Doesn't look too hard to check but I've never done it.

 

It's not the valve train. Going to keep on driving it. Either it will keep running or it'll break. Btw spike, what part of Harrisburg are you in?

 

In a "box" with its points being Hummelstown / Hershey / Middletown / Elizabethtown.

 

I have the same symptoms. Yesterday let the car warm up for about 15 min and the sound was gone. Got in it today and it was back. Noticed that I don't hear it if I rev in park or neutral. Wonder if it's related to the transmission, but the sound seems to come from the passenger side.

 

Sounds just like mine.

 

Passenger side is where the mice chewed off all of my sound dampening foam insulation for a nest on top of the cabin air filter (behind glove box). No wonder that side is louder.

 

Hey spikeman, we probably live very close to each other, and mine plummeted as well. I just attributed it to winter gas.