SilverSled

Question- my mileage has dropped over the past few weeks or so from 21 around town to 13 to 17.

I did just replace my belts (two serpentine) and I could have overtightend them (power steering squeeks and wanted to make sure new belt wasn't slipping). But, I doubt it's from an over tight belt or two.

We bought this 2002 ES300 used with 110k miles on it and they have 'proof' of plugs being changed at the dealer in the manual.

Air pressure in tires is right on. I've done a number of throttle body cleanings w/ Amsoil Powerfoam over the past few years we've owned it.

What should I focus on first?

Plugs or O2 sensors? For heaven's sake there are 4 of them and it's $540 for all four!!

I hate to spend that money and not KNOW that's my problem...

Any Help??

Thanks all.

SilverSled

Weather has been colder lately, I do wonder about gas mixes and if they've changed it much w/ the weather.

Still seems like a big drop.

SilverSled

A friend just sent me this email he found...

As if we really needed another reason to hate winter.

Those of you living in northern climes have already started to notice the seasonal decline in fuel economy, even with careful attention to sagging tire pressure (probably the best known effect of the mercury's slide).

Yet, despite diligent all-around maintenance and continued careful driving, cold weather fuel consumption can be dramatically worse than in warm temperatures.

How much worse?

Have a gander at these calculations for a Honda Civic hybrid at 60 MPH in varying ambient temperatures:

MPH-----AMBIENT-TEMP-----MPG (US)

60------------95----------52.98
60------------85----------52.62
60------------75----------51.16
60------------65----------49.12
60------------55----------47.22
60------------45----------44.67
60------------35----------43.05
60------------25----------41.54
60------------15----------39.41
60------------05----------38.09

Look at the extremes: the coldest MPG is 28% lower than the warmest.

My own experience supports this: 12.5% worse mileage during the colder half of the year (Oct 15 to Apr 15) than for the warmest half (Apr 15 - Oct 15), on average 2002-2004 in my 1989 Accord. Comparing just the warmest months (Jun-Aug) to the coldest (Dec-Feb), the difference is even more apparent - 21.2% worse.

Why so bad? Off the top of my head, I could think of a couple of reasons to explain it, but together they didn't seem significant enough to account for the magnitude of the change. With this mystery to solve, I hit Google. And here's what I learned...

9 reasons your winter fuel economy bites

1. More idling

This should be a no-brainer, yet parked idling cars are a common sight in cold weather. Resist the temptation to idle your car to warm it up. An idling engine gets 0 mpg. Consider also that idling the engine does nothing to warm up the tires and drivetrain.

Even in the coldest weather, you can begin driving after 30 seconds from a cold start - keep speeds low/moderate and use gentle acceleration until the temperature gauge starts to climb (source).

2. Low tire pressure

Of course you're smart enough to keep up your tire pressure as the temperature drops, right? A 10-degree (F) change in ambient temperature equates to a 1 psi change in tire pressure (source). Fuel economy declines 0.4 percent for every 1 psi drop (source).

3. Increased rolling resistance

Even if you're completely attentive to proper tire pressure, cold ambient temperatures will still cause your tires to return worse mileage. That's because a tire's shape isn't completely round - the sidewall bulges out at the bottom, and where the tread meets the road the small contact patch is actually flat. As the tire rotates, it constantly deforms to this shape, and this deformation requires more energy when the rubber is cold and hard. Rolling resistance at 0 degrees F is 20% greater than at 80 degrees (source 1, source 2).

4. Crappy road conditions

It's increased rolling resistance of another kind: driving through slush and snow. And then there's its wasteful polar (no pun intended) opposite: no friction at all! (A.K.A. wheelspin on ice.)

5. Lower average engine temperature

In the winter, an engine takes longer to reach operating temperature and cools off faster when shut off. Since the engine management system orders up a richer mixture when cold (proportionately more fuel in the air/fuel combination), more fuel is being burned overall.

A block heater can offset this problem (improving fuel economy by 10% in sub-zero conditions - source), as can garage parking, and combining trips (to minimize the number of cold/hot cycles).

Also related...

6. Higher average lubricant viscosity

Engine oil thickens as it cools. So does transmission and differential fluids and even bearing grease. Significantly more energy is needed to overcome the added drag these cold lubricants cause.

Using synthetic fluids can address this problem, since their viscosity changes less at extreme temperatures than traditional mineral fluids.

7. Weaker gasoline

Gasoline doesn't vaporize readily at very cold temperatures. So oil companies formulate fuel differently for cold-weather markets in the winter. Unfortunately, the changes that provide better cold vaporization characteristics also result in less available energy for combustion. You won't get as far on a liter of winter gas as you will on a liter of summer gas. (Source.)

8. Higher electrical loads

In colder temps, you use electrical accessories more often:

- lights (in higher lattitudes it's darker in the winter)
- rear window defroster (because it's easier than using the ice scraper, right?)
- heater blower motor (I don't have a/c, so this isn't balanced out during warm conditions); heated seats/mirrors
- windshield washer pump (because it's easier than using the ice scraper, right? And for frequently cleaning off dirty road spray.)

9. More aerodynamic drag

No, I'm not referring to the layer of snow you're too lazy to brush off the top of the car (though that would hurt mpg too).

A vehicles aerodynamic drag is proportional to air density, and the density increases as temperature drops. For every 10 degree F drop in temperature, aerodynamic drag increases by 2% .


Sorry to get so technical but this is whats really going on most likely

__________________




Now I wonder if I should change O2 sensors at all? One the other hand, this car now has a good 125K miles on it, likely w/ original sensors to boot.

mooseboy84

O2 sensor has nothing to do with gas mileage. If you say you noticed it after overtightened your belts, loosen the belts.

SilverSled

Nothing to do w/ mileage? Really? What sensors do if not air/fuel ratio sensors?

Did find tire pressures down to 34 (1) and 37 psi other three (44psi tire setting). Refilled those.

Any other advice?

PFB

Also make sure that none of your break callipers is stuck.

Test by putting the car on a level ground, turn engine OFF, shift to Neutral, and push it slightly back and forth. See if it moves freely

Phil

88Legend

O2 sensors have everything to do with gas mileage, engine performance, and emissions. They try to keep the engine at a perfect 14.7:1 air fuel mixture. If the O2 sensors are getting older and slower the mixture will not be the "perfect" 14.7:1 anymore.

The O2 sensors in new cars like your 2002 last usually about 100K-120K miles. They don't show the check engine light until they are past a certain level of "slowness" if you will. Your car is at the mileage where these things start dying.

I just replaced mine today on my Legend. I got the parts at Autozone for 50. But I have the old style one-wire unheated O2 sensors in my old beast. My car is getting better mileage and the engine doesn't hesitate or stall anymore. Yours are probably the 4 wire Planar-type sensor. They are more expensive but you can replace them your self pretty easily. If you do this get a O2 sensor socket. It makes life much easier.

There is a way to test them with a volt meter to see which one is sluffing. Also check the condition of the plugs. If they are fouled or white then your mixture is way off. Mine were white meaning a lean mixture.

Lexmex

You have to make a good distinction here on A/F sensors and O2 sensors. They can be used interchangeably. I like to refer to A/F or Air/Fuel Sensors as those upstream sensors that run before the main catalytic converter and those do matter. The O2 sensor I like to refer to is the one after the main catalytic converter underneath the vehicle and that is an emissions related component.

One thing I did like about cold weather when I raced the 1/4 mile was that nice air density that just gave us beautiful times.

88Legend

Haha, my car only has 2 O2 sensors. One on each exhaust manifold. None near the cat.

llcoolpass

what a lot of people here are saying is right on. and dont forget gas pump variances. youd be surprised how inaccurate they are allowed to be by law.

but if this continues at diff places and in different conditions, in short, get the car checked out. basic maintenance [fuel filter for instance] and have the brakes and suspension checked. have the computer checked for 02 sensors function.

SilverSled

Yes, I was actually being a tad sarcastic w/ Mooseboy. O2 sensors are hugely responsible, mass air sensor slightly less so.

You did just answer my next question however, on how long the O2 sensors should last. Yes, just checked mine..... 129k miles! Yikes, how time flies.

Those air/fuel sensors must be the wide band type... YIKES are they steep. Twice the old O2 sensor type.

Reading old posts, it seems the ES300 has 2 sensors forward of the cat and 2 rear ward. The forward ones are the A/F type and the ones after the cat are the old cheaper ones.

For fuel mileage, I'll replace the A/F sensors first as those are most likely the culprits if any sensors at all are. As mentioned, these ones are OLD.

SilverSled

Agreed, my 420HP mustang sure likes more dense air/ oxygen as well. That is when I don't squirt a small shot of 'go fast juice'.... Don't get to race like I used to before my two young cheribim were born though..... 8-)

88Legend

Oh yeah the fuel filter. That is a good idea. Especially after that many miles. I would say distributor cap and rotor, and plug wires but...your car wasn't made in the 80's like mine...

llcoolpass

i once saw a legend , 2dr, with a 6spd. i dont know how it could be, but I really saw it. its about as rare as my car in stick, i would say. i think it was early 90s , not 80s model. now THATS a legend. lol

88Legend

Yes the second gen came with an optional six speed. But the first gen came with an optional 5 speed. These are the Legends that had the option if the six speed. This is how many of each one is left on the road. These numbers are for the autos and six speeds, so probably about a third of these are six speeds. So the total is a little under 16K...so there are about 6-7K six speeds left on the road today.

http://www.acura-legend.com/vbulleti...legends-54853/

Only the L, LS 1993-1995 coupes came with the six speed and the GS sedan.

Sorry for the thread highjack...