I checked my Gas Cubby records to be sure this isn't normal... For the past two summers I've been averaging approximately 32 MPG in the summer (AC running almost constantly; 34 MPG is my annual average). The past couple of months, I've only managed 27 MPG. My daily drive is the same, my driving style is the same, nothing has changed. I've never even had a single CEL in this car. It's been mechanically the most perfect machine I've ever driven. Literally NOTHING has ever gone wrong with it. Had it checked recently for a trip and everything A-OK and maintained according to schedule. Had the oil changed less than 1,000 miles ago, just dropped in a new air filter. It's not stuttering or exhibiting any other symptoms of an ignition problem. I'm sorta baffled. Any similar experiences or otherwise any thoughts?

2007 base 5-speed, Pirelli P4's slightly overinflated, 76,000 miles.

 

same as well. does anyone know why?

 

Check your tire pressures.

 

Have you had your valves adjusted?

 

Throw in a little iso heet(1/2 a bottle) with Shell,Mobil premium. It will slowly clean the carbon and clean the injectors. I just did that and I am getting 49 mpg according to the ultra gauge. 160 miles on a quarter tank.

 

Recently I have had a Motorvac Fuel Injection and de-carbon service done.
"It included cleaning the upper intake plenum and throttle body of carbon and gum (trident?) cleaning the fuel injectors and rails and removing carbon from inside the engine. Restores fuel economy, smoother idle and better performance for your engine."
That was what the print out said after I paid the bill. ($180.)
Seems to run better and is on track to getting better than my average of 36.5 mpg of spirited driving. I have a 07 sport silver with 105k.
I have only owned it for 3 months and after purchasing it I also had new front pads and rotors, drive belt, flush brake fluid, flush clutch fluid, service trans fluids and replace the spark plugs.
I thought that, as the miles were getting up there, that fresh everything would be a good idea. Hope this helps. Good Luck

 

I keep the tires around 38 psi, FYI.

I should also add I THINK I'm down on power. It's hard for me to gauge, but it does seem like I have to bury my foot more than in the past just to get up to speed, and it feels more slugging than usual when accelerating. The other day I got beat to death by another Fit from a dead stop. Yeah, he might have gotten the jump off the line, but we're talking Fits, not Ferraris. He shouldn't have been able to clear four car lengths in less than a quarter mile with my foot kicking the loud pedal. We weren't racing, FYI, just trying to not get runn'ed over by aggro dudes in bigass trucks.

I didn't really suspect valves though, as it's not quite to the mileage that it's recommended, and it's not making any more noise than usual. I usually apply the VW test to determine time to do valves (when it sounds like a Beetle, tune it up).

Question about the fuel system cleansing... I've heard from reputable folks that the procedure can often cause more harm than good by knocking all that crud loose and sending it downstream. I've never had that done with any of my cars in the past, but it actually helped?

Could it have anything to do with coil packs or plugs? It did almost stall one time and one time only. Don't really notice much shuddering, but like most slow brewing issues, that could be something I've just gotten used to. Kind of reluctant to pull those bits on a blind hunch cause it's a real pain for a sauagefingers.

 

Valves adjustment is a good idea but you want to de-carbon the motor gently. Look for Redline total fuel cleaner and use a quarter bottle 1 tank and add 1 oz for the rest. After the 3rd or so tanks get the valves adjusted and change the oil. Using a machine is to harsh and all that carbon will foul o2s and could damage the Catalytic converter. My brother in law wrecked his car getting his car ready for inspection. That's why I said use a premium grade gas like Shell, Mobil they advertise more cleaning agents and BP but not available everywhere.

 

Good move, clean slate specially with the miles driven and if you don't know the history...

 

It's summer in Texas and you are getting 27 MPG.... Sounds pretty normal to me.... I have a hard time explaining to Yankees that high temperatures kill your fuel mileage... They all claim their mileage improves in hot weather... It was 108.1 today just before a thunderstorm that lowered the temperature and brought very little rain. Even with a supercharged engine I am also suffering a big loss of the power increase but not all of it thankfully. You can lower the intake air a little by using washers as spacers and longer bolts to place between the hood and the hinges to allow heat (that rises) to escape.. When sitting still you can feel it rising from the opening and it is going to exit more quickly at speed. Using colder spark plugs will lower combustion chamber and exhaust sensor temperature allowing more ignition advance as will using premium fuel..Using an injector cleaning product will clean the entire fuel system the backs of the intake valves and the combustion chamber of carbon improving the function of the injectors by loosening any particulate that is altering the spray pattern and carbon removal eliminates hot spots that cam cause knocking or pinging that will cause the ECU to pull back ignition timing advance and increase the amount of fuel being added to the air/fuel ratio..

 

There is a ton of factors here. First off engines do tend to become less effiecent over time as the gum up with carbon and old oil. The cat gets more and more clogged which hurts your power and economy. Injectors get clogged, fuels fliters etc. Also are your tires wearing down? Maybe time for a rotation or new tires.

The heat really does kill power and mileage so thats normal. You could get all the above checked out but those are all the common things that can hurt economy power etc.

 

In Tempe I'll bet power loss is worse because of the lack of humidity... Humidity is good for combustion chambers but wreaks havoc on A/C units, dogs, old people and babies.

 

[quote Using colder spark plugs will lower combustion chamber and exhaust sensor temperature allowing more ignition advance as will using premium fuel..[/quote]

Hey TC, I've noticed that you talk about the use of premium fuel in yur ryde so today I fill'd my "empty" tank with premium for the first time since I've owned it. I immediately noticed an increase in power as well as throttle response time. From the low to mid to high rpm ranges there is a very distinguishable improvement.. I have to use this tank of fuel up to see if any mileage gains took place tho. Thanx..man, I should have tried this a long time ago... Problem now is can I afford to use premium all the time.

 

How is humidity good for combustion? Its water that should hurt combustion plus it causes rust.

The heat here just stucks. Destroys everything made out of rubber, kills your power, A/c systems die in record time and finally batteries barely last 2 years if you are lucky. I need to move to San diego but they wouldn't like my civic or the fit. Screw smog laws.

 

The heat here is nowhere near what you have to endure and it's not heat that get's yur ryde all screwed up here, it's the salty moisture from the ocean. It's fairly warm mostly year 'round which may make it appear hotter than it really is. Humidity is not all that great either...But of all the things you mentioned rubber, batteries and ac systems I've never had a problem with them. But the heat does kill the power a bit.. Did live and own a car here before

 

I know the heat is horrendous this year, I still just can't get my head around a 5-7 MPG loss (50 miles per tank) compared to previous summers, 8-9 MPG of yearly average and 10-12 MPG off my highway average.
(Gas Cubby is a great little app, by the way)

Tires are 7 months old. Oil is synthetic and changed regularly. I suppose gear oil could use a swap. Plugs should have another 25k mile son them, and when I checked them at my 60k tuneup they were like new with a little cleaning, but I suppose it could be time. And I know being down on power I'm burying my foot more than usual. I usually granny shift at 3500, but lately have been running it up to near redline just to get it up to speed. So that's not great.

I think it's just a number of issues working together to kill fuel efficiency. I'll start with a gradual fuel system cleansing then move to more checks like valve clearance if that doesn't seem to help.

At least my AC system is in good shape! One thing about small cars, they cool down pretty quickly, so I'm not running full-blast the entire time I'm in the car.

 

Have the fuel filter checked as well. If that is clogged it could be the issue as well. You may want to invest in a drop in K&N filter as well since they are so much better that the crap paper ones. Also maybe have your alignment checked? It could be off and that causes extra wear on the tire and such. To me it just sounds like you are reaching that point of needed a solid maintence going through.

Oh and have the coolant checked/drain or flushed if it is really dirty.

 

Water is hydrogen and oxygen. Hydrogen is very combustible combustible and without oxygen there is no combustion High humidity cools the combustion chambers and dissipates heat through evaporation... Water/methanol injection with a 50/50 mix of the two cools and increases octane and by doing that the ECU responds by adjusting the ignition timing to increase advance and adjust the A/F ratio/. Fuel mileage and and engine performance is increased as is the longevity of the combustion chamber by eliminating carbon that can form on them causing hot spots by glowing that result in pre ignition and knocks and pings.

 

Quote:

Originally Posted by Texas Coyote

Water is hydrogen and oxygen. Hydrogen is very combustible combustible and without oxygen there is no combustion High humidity cools the combustion chambers and dissipates heat through evaporation... Water/methanol injection with a 50/50 mix of the two cools and increases octane and by doing that the ECU responds by adjusting the ignition timing to increase advance and adjust the A/F ratio/. Fuel mileage and and engine performance is increased as is the longevity of the combustion chamber by eliminating carbon that can form on them causing hot spots by glowing that result in pre ignition and knocks and pings.

Wow yeah I know you need oxygen for combustion. I also think it water/methanol is very very different than gasoline. For instance if you just put water in your gas tank with regular pump gas it will kill your car. Same goes for getting water in the intake or exhaust. Now I realize that is different than the moisture in the air but what you are saying is that the combustion chamber of a car has the ability to break down water into its base elements which again I don't think is correct (isn't this what hydrogen fuel cells attempt to do?) Finally if the air temperature is around 100+ degrees with high humidity it is still very possible you are getting little to no cooling effect from the water in the air. Also lets not forget there is a lot more in air than just oxygen as well and the same goes for that moisture in the air. Like others have said it can have salt and other things in it that do cause harm to an engine.

I still think that overall air temperature effects your power and MPG more so than humidity on its own. If you are talking about getting better mileage after a cool rain or during the colder months I would agree you will see better gas mileage but I feel it is still due to the air being colder and denser. That’s just my thoughts. I tried googling for more answers but there doesn't seem to be anything definitive. Anyways isn't it more productive to give him suggetsions on things he can do to help fix the issue? Not much he can do about the weather.

 

AZ heat is definitely a battery killer but preserves the car. Have a classic, take it to AZ to preserve it.

HI weather definitely eats up the car but definitely preserves the sanity... must be the umbrella drinks, grass skirts and the Poi...
TGIF all!!!