WTH is going on with my mileage??? - UPDATED with more stumpage!!!

[MaxFusion16]

is your engine always cold or takes long to warm up?
could be your thermostat, it could be stuck open causing coolant to circulate even though engine is cold.
cold engines are not as efficient burning fuel as when warm, so you could have unburnt fuel left in your cylinders, thus lowering the MPG.

 

[Don Vito Corleone]

Originally posted by: MaxFusion16
is your engine always cold or takes long to warm up?
could be your thermostat, it could be stuck open causing coolant to circulate even though engine is cold.
cold engines are not as efficient burning fuel as when warm, so you could have unburnt fuel left in your cylinders, thus lowering the MPG.

I know. I had a mechanic check the thermostat, O2 sensor, and fuel delivery/injection system - everything checked out fine.

 

[jagec]

Originally posted by: DonVito

Originally posted by: iamwiz82
Are you running the defroster a lot? Defroster = AC.

Not particularly. Just as in Washington, I only run the defroster until the windshield is clear, then switch to panel/floor vents. The car has automatic climate control, and obviously, being in MN, I have used the heat pretty much constantly for the last few months.

Before I rewired my VW, it would turn on the AC even when you were blowing hot air through the defogger.

 

[StageLeft]

Originally posted by: Vic

Originally posted by: jagec

Originally posted by: iamwiz82
Are you running the defroster a lot? Defroster = AC.

I hate how auto manufacturers do that. I actually rewired my VW so I have an AC SWITCH, and I can choose whether I want my AC on or off.

Yeah, I really hate that as well.

Me too. Can't freaking stand it. I generally drive with AC off, unless it's very hot outside or mrsskoorb is complaining about "dampness". I hate the wear on the system, and more importantly the extra energy it uses in terms of gas and decreased performance (even if negligible).

 

[flot]

The only reasonable mechanical explanation I can think of that hasn't been obviously ruled out is that you could just plain have a fuel leak. Possibly a leaking/sticking injector (?) but I think you'd notice that in driving. (maybe not though?)

You *shouldn't* with an 01 but it's not an impossibility. Does your car pre-pressurize the fuel system when you first turn the key to "on" ? Does it seem like it takes a long time? If you let it pressurize, then without starting the car, wait ~15 mins and cycle it again - does it have to re-pre-pressurize it?

Edit: By the way, how are you calcuating your milage? Are you going by an on-board-computer or the like or actually dividing miles driven by gallons of gas purchased?

 

[PricklyPete]

Originally posted by: iamwiz82

Originally posted by: njmodi

Originally posted by: iamwiz82

Originally posted by: njmodi

Originally posted by: iamwiz82
Spark plugs are due, if they haven't been done yet.

The plugs might be at faulty, but they are definitely not "due" as a maintenance item - his car has platinum plugs, with 100k replacement intervals.

Sorry, that is a silly thing to believe, IMHO. I can get spark plugs for $2/plug, $12 seems like a small price to pay.

Show me some NGK platinums for $2 each.

Why must every import driver swear by these? 😕 It is almost as dumb as quadruple fires, +84s, or, even plutonium plated. It's amazing how much money companies can make on stuff like that.

Because we've experienced poor performance when using generic plugs from Autozone. I bought some Bosch platinum plugs from Autozone to replace my NGKs in my old Millenia. The cars performance plummeted (and yes, I replaced them properly). Went and got some NGK iridium for $7 a piece online and the car went back to performing fawlessly.

 

[Don Vito Corleone]

Originally posted by: flot
The only reasonable mechanical explanation I can think of that hasn't been obviously ruled out is that you could just plain have a fuel leak. Possibly a leaking/sticking injector (?) but I think you'd notice that in driving. (maybe not though?)

You *shouldn't* with an 01 but it's not an impossibility. Does your car pre-pressurize the fuel system when you first turn the key to "on" ? Does it seem like it takes a long time? If you let it pressurize, then without starting the car, wait ~15 mins and cycle it again - does it have to re-pre-pressurize it?

Edit: By the way, how are you calcuating your milage? Are you going by an on-board-computer or the like or actually dividing miles driven by gallons of gas purchased?

I have no idea how I would tell whether my car is pre-pressuring the fuel system. The car always starts instantly, and has not exhibited any recent issues with starting.

I calculate my mileage by dividing the gas I purchase into the number on my trip odometer, which I reset everytime I buy gas.

 

Originally posted by: Vic

Originally posted by: Eli
If you're trying to extend the life of your engine, use the stock paper filters, do not use AMSOil, K&N or similar filters.

They flow more air, they do not filter as well. Period.

I don't agree with this statement, Eli. The benefit of the oiled renewable filters is that they last MUCH longer (actually making them a good investment in the long run), and that they flow more air even when dirty.
Everyone knows that mechanics (and particularly quick oil change shops, whose employees are not mechanics) try to fool customers into believing that a dirty paper air filter can damage an engine by allowing dirt through, but this is completely untrue. What actually happens with a paper air filter when it gets dirty is that it clogs, reducing airflow and worsening power and gas mileage.
The renewable filters, like K&N's, do not clog anywhere as bad, and actually increase effectiveness over time (to an extent).
Also, paper filters can only filter at only layer. K&N style filters can filter over multiple layers. This means that they can flow better and still filter effectively.
Text

They don't filter as effectively as a paper filter, never have, never will.
They let more air through as well as more and larger particles that can, over time, damage your engine. I'll stick with my paper filters.

 

[flot]

Originally posted by: DonVito
I have no idea how I would tell whether my car is pre-pressuring the fuel system. The car always starts instantly, and has not exhibited any recent issues with starting.

I calculate my mileage by dividing the gas I purchase into the number on my trip odometer, which I reset everytime I buy gas.

On many cars you hear a faint buzz when you first turn the key to "on" in the morning. That is _usually_ the fuel pump pressurizing the lines.

As for the odometer - not to suggest something stupid - but are you sure it is accurate? (seriously)

 

[Don Vito Corleone]

Originally posted by: flot

On many cars you hear a faint buzz when you first turn the key to "on" in the morning. That is _usually_ the fuel pump pressurizing the lines.

As for the odometer - not to suggest something stupid - but are you sure it is accurate? (seriously)

Huh - I've never heard this buzz, but again, the car starts as easily as it ever has.

I had thought of the odometer - it occurred to me that, even though they're nominally the same size, the Turanzas might be smaller than the Potenzas, leading to more RPMs and the speedo and odo showing inaccurately high speeds/mileage. I think that's unlikely, though - according to Tire Rack the tires are within 3 rotations per mile. The odometer is certainly accurate enough that my ballpark "tests" (i.e., driving between two points with a known distance between them) show no problems.

 

[imported_Phil]

Originally posted by: J0hnny

Originally posted by: Hi
have you changed your motor oil to see if it helps

Same problem in my Civic (but i drive a lot of city), here is what i did to fix:

0) Fuel injection cleaner (chevron techron)
1) New fuel filter
2) New spark plugs
3) Changed oil and oil filter
4) Cleaned air filter
5) New plug wires
6) Cleaned throttle body w/ throttle body cleaner
7) Reset ECU

Milage improved by an extra 50 miles to the tank after that (city driving). I still think I can do better, so I'm going to

possible 8) Clean IAC
possible 9) change ground wire

Shens on the whole "p00n" thread.

/Threadjack

 

[Don Vito Corleone]

Is it possible I could have a significant alignment problem without the car pulling laterally to some degree? I've never noticed any side-to-side instability whatsoever.

Also, could a fuel filter really create this kind of sudden, huge drop in mileage?

 

[Vic]

Originally posted by: DonVito
Is it possible I could have a significant alignment problem without the car pulling laterally to some degree? I've never noticed any side-to-side instability whatsoever.

Also, could a fuel filter really create this kind of sudden, huge drop in mileage?

Yes, it is possible to have an alignment problem without the car pulling, but there would be other noticeable symptoms, like excessive and uneven tire wear and/or poor handling.

I don't think a faulty fuel filter could cause this kind of problem. If anything, you'd think that gas would have a harder time reaching the engine.

 

[Don Vito Corleone]

UPDATE 3/11: Just came back from my mechanic. The alignment and brakes are fine. Still no idea what the hell's going on. He says he's willing to keep looking, but it seems like a waste of $80/hour, when the car runs fine. Grrrrrr . . .

 

[Vic]

What's the traffic like out in MN? Is it like California and the Mountain states, with much higher speed limits and big wide boulevards with everyone punching it and screeching tires at every intersection?
What I mean is, have your driving habits changed?

 

[cavemanmoron]

Originally posted by: SampSon
Winter gas and the extreme cold weather will cause a drop in gas mileage.
The tires could have more rolling resistance than your old ones.

winter fuel is worth a loss of about 15-25% of your fuel mileage.

wait till May,see if it goes back up.

inflate tires to Max on sidewall.

some tires are max 35psi,some 41,read the sidewall.

 

[Don Vito Corleone]

Originally posted by: Vic
What's the traffic like out in MN? Is it like California and the Mountain states, with much higher speed limits and big wide boulevards with everyone punching it and screeching tires at every intersection?
What I mean is, have your driving habits changed?

I probably am doing more city driving, but the problem started when I was still in Washington, with the same driving patterns I always used. Also, I got some of my worst mileage while driving cross-country on the interstate.

 

[Don Vito Corleone]

Originally posted by: cavemanmoron

Originally posted by: SampSon
Winter gas and the extreme cold weather will cause a drop in gas mileage.
The tires could have more rolling resistance than your old ones.

winter fuel is worth a loss of about 15-25% of your fuel mileage.

wait till May,see if it goes back up.

inflate tires to Max on sidewall.

some tires are max 35psi,some 41,read the sidewall.

At this point, since I seem to be having no luck, I'm thinking I'll do just this, more or less.

I will only stick with the higher tire pressure if it does some good though - it hasn't in the past, and it creates a harsher ride.

I will also try Techron fuel system cleaner on my next couple of oil changes (not that I think it'll do any good . . . ).

I'll revisit the problem in May, and if I don't see some progress, I may just get a new car. This is crazy . . .

 

[kevman]

these cars are known for the Mass Ari flow sensor going bad, have that changed, and get the ECM reprogrammed by the dealer. it could be a coincedence that it happend during the time tires were replaced. also you may want to try BG44k in the gas tank before your next fill up.

 

[kevman]

Also, does you car exhibit any drivablilty problems such as vibratoins etc ? may that the tires re out of round or the wheels are not balances probperly.

 

[rahvin]

I would wage that given the timeframe you live somewhere that switched to partiial ethanol fuel during the winter (lowers gas mileage) combined with new tires that get better traction (better traction means higher rolling friction and will lower gas mileage), in addition to larger tires getting worse gas millage. Wait till you get the summer gas back and see if it improves, if it doesn't you probably wanna have the fuel system (injection, sensors etc) checked to make sure it's not running rich.

 

[TwoBills]

At this point, since I seem to be having no luck, I'm thinking I'll do just this, more or less.

I will only stick with the higher tire pressure if it does some good though - it hasn't in the past, and it creates a harsher ride.

I will also try Techron fuel system cleaner on my next couple of oil changes (not that I think it'll do any good . . . ).

I'll revisit the problem in May, and if I don't see some progress, I may just get a new car. This is crazy . . .[/quote]

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At this point I think you've covered all the bases. We're all stumped. A can of BG44K wouldn't hurt, but you don't seem to be the type of driver the lugs the engine, so I don't think that will help. Alignment? On second thought, nah. Give the high psi a shot for a month and see what that does. Same w/the Chevron, couldn't hurt. As a last resort, see my sig. Get back to us in the spring. We'll probably all end up w/a big DUH.

 

[psteng19]

Originally posted by: Vic

Originally posted by: DonVito
Is it possible I could have a significant alignment problem without the car pulling laterally to some degree? I've never noticed any side-to-side instability whatsoever.

Also, could a fuel filter really create this kind of sudden, huge drop in mileage?

Yes, it is possible to have an alignment problem without the car pulling, but there would be other noticeable symptoms, like excessive and uneven tire wear and/or poor handling.

I don't think a faulty fuel filter could cause this kind of problem. If anything, you'd think that gas would have a harder time reaching the engine.

Not a faulty one, but I've noticed after changing out the fuel filter, I got worse mileage with the new filter for a couple of tanks.
Could've been coincidence since at the time I got it changed, it was changing over to winter (last December).
Mileage is just consistently bad now.
I'll have to wait until summer to see if my mileage jumps back up to 45 mpg.


Here's something that I've also noticed that could solve this mystery.
Do you always fill up at the same gas station/pump?
Different pumps (even in the same gas station) fill up to different amounts.

The one station that I regularly go to fills up to about 11 gallons, whereas other stations I fill up at only get my tank to about 9 gallons.
I normally fill up when the needle is just about touching E so it should be roughly the same volume each time.

So if you fill up one day at the pump that only gets you 9 gallons (tank is not actually full), and you observe 300 miles in that "tank full"...
On the next fill up, you use the "better" pump that gets you 11 gallons (full tank on this fill up)...
Then you will observe incorrect gas mileage.

300/11 = 27 mpg (wrong calculation)
300/9 = 33 mpg (correct calculation)

It is for this reason, I try using the same station, same pump each time.

 

[Don Vito Corleone]

Originally posted by: TwoBills



At this point, since I seem to be having no luck, I'm thinking I'll do just this, more or less.

I will only stick with the higher tire pressure if it does some good though - it hasn't in the past, and it creates a harsher ride.

I will also try Techron fuel system cleaner on my next couple of oil changes (not that I think it'll do any good . . . ).

I'll revisit the problem in May, and if I don't see some progress, I may just get a new car. This is crazy . . .

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At this point I think you've covered all the bases. We're all stumped. A can of BG44K wouldn't hurt, but you don't seem to be the type of driver the lugs the engine, so I don't think that will help. Alignment? On second thought, nah. Give the high psi a shot for a month and see what that does. Same w/the Chevron, couldn't hurt. As a last resort, see my sig. Get back to us in the spring. We'll probably all end up w/a big DUH.[/quote]


I'm thinking that, although I have a high-quality tire pressure gauge, I'll try buying a new one and double-checking the pressure. By dumb luck, a woman from Minneapolis just called into Car Talk with almost this exact question, in relation to her Subaru, and that was their recommendation - it couldn't hurt.