Help! My FE has dropped
 

I've been averaging 29MPG through the winter on my 98 Corolla - 100% city driving here in Vancouver. As the weather has warmed up, I was expecting my FE to go up even more. But instead, the last two tanks have averaged 26MPG and it looks like the current one will be the same.

I'm doing more coasting than ever. Engine off at lights. Safe drafting whenever possible. I feel my that my hypermiling is better than ever, so a drop heading into the summer is especially troubling.

Before I noticed the drop, my mechanic adjusted the e-brake tension and cleaned the brakes. I don't think the brakes are dragging because the neutral coast seems to be as good as before. Oil has just been changed. Tires always at max 35psi. What am I missing? I think I'll change gas stations to see if they're doing anything funny with the mix.

I'd look at the air filter, plugs or maybe the muffler.

Pump the tires up to 50 psi. I had the same problem.

Air filter looks clean. Plugs were changed less than a year ago. What should I look out for on the muffler? The car doesn't sound any different and I haven't noticed any loss in power, although given how lightly I drive the car, I probably wouldn't even notice any reduction in power.

Thanks.

Loss of power would be the first sign. Rough running or trouble cranking would be another. Just the age of the car made me think it may have never been replaced. They do eventually get stopped up or rust out over time.

It still could be the gas.

Has traffic increased that you noticed' holiday weekend traffic?

Are you driving with the windows down any at all since it's "warmer".

What about the battery; weak batteries need to be charged more and the extra drag of the alternator could reduce mileage.

what about the fuel filter? has it ever been changed? it made a descent difference for me.

Thanks for the additional suggestions. The fuel filter in this car is in the tank and is not meant to be serviced - it was designed to last the life of the car.

The battery is only 2 years old and shows 12V with engine off, and 14V with engine on. It should be good for years to come.

I'm very conscious with the windows and A/C use. Usually just open a crack in the left-front and right-rear windows to get a good cross flow.

Nothing out of the ordinary traffic-wise. I make a lot of short trips <5km, so it's quite frustrating for me because I know the car can do a lot better. I've managed to cut down at least 33% of my driving by riding my bike this month. I'd love to get an electric assist bike, but they're still quite pricey and it'll probably get stolen real quick.

I'll have to have a closer look at the muffler. It almost certainly has not been replaced. How long do they usually last anyways? I recently had to change the starter contact points, so if there are any more major expenses, I might use it as an opportunity to trade for a 9th gen Corolla or an Echo for even better FE.

maybe its the changes in driving style that you think would improve mileage actually arent. have a scangauge?

could try driving more like you had in the past and see if mileage is affected up or down.

on the e-brake, if they happened to be draging, at a loss of 3mpg i'd imagine you would have smelt it when you get out of your car. you might jack up each wheel and give it a spin to eliminate it for sure though.

check engine light isnt on im assuming?

check how your tires are wearing, possible alignment issue...

thermostat operating at correct temp? acording to my scangauge, my old stat was running about 150, with the new 180. without some sort of scanner i wouldnt of known, the gauge in the dash reads virtually the same as before.

making more short trips? may have a stronger negative affect than improved driving style helps.

...and then back to a scangauge, assuming you dont have one. before ever having one, i could have tanks of gas vary by as much as 4mpg from one to the next, and not know what i did different if anything to cause it. with a scangauge i can see how my driving is affecting mileage.

My car does this when they go from Ethanol enriched winter gasoline to the straight gasoline. Find a gas station that is still using Enriched gas and see if it helps...

Shouldn't FE go up when switching from Ethanol "enriched" to straight gasoline? Is that the main difference between summer and winter blends? Since I only started logging fuel economy last summer, I don't have too much historical data to compare to.

Good idea. Think I'll give that a try this weekend. Thanks.

I don't have a Scangauge, but I can monitor a lot of the OBDII data (see my other thread on "possible Scangauge alternative"). Temperatures are normal and Check Engine Light is not on.

That is traditional wisdom, however, there's probably more to it. If your car is tuned for E10 then it would get better mileage from it. Do cars learn fuel the way they learn driver style?

Yes, they do 'learn' the fuel. The timing maps and fuel trims will adjust but that usually only takes the first couple of gallons or at most a whole single tank to make changes if the fuel changes. With E10 the computer learns to richen the mixture out ever so slightly and gives a little extra timing.

Some cars get worse mileage and run like crap because even though the octane is the same the amount of fuel required is a little higher and some fuel systems don't compensate for that either because they have bad O2 sensors or they're carbbed. It isn't THAT much of a change but if the engine is on the edge of running lean as is then you put E10 and no corrections are made then it's overly lean.

I thought that when they add ethanol to gasoline, they do it so that the end result is at the same octane rating as they're selling it -- so they replace other octane enhancers with ethanol. In short, I thought E10 87 octane is still no higher than 87.

Pump octane is a bit arbitrary, some mixtures might burn faster or slower than others, despite having the same "knock" value.

Remember that the octane rating at the pump isn't a maximum number, it's a minimum.

Did a little more reading and they do in fact keep the same octane level. And because of the Ethanol it's possible for the fuel to fall below the rated octane on the pump by as much as 3 points as the fuel ages and moisture gets introduced. We run 86 octane up here but I'd love to run some 84! If it ain't pinging it's not low enough!

I would jack the car up and check front and rear brakes for dragging. He may have gotten the e/brake a little too tight or it is possible you have a caliper sticking. I had my mileage drop like that one time it ended up I had a wheel bearing that was bad. Couldn't tell it in driving and it wasn't grinding, but when I jacked the car up there was alot of play in it. It just wasn't rolling freely.