Ethanol or winter leading to bad mileage?

[jubal]

My 2000 4runner is getting horrible gas mileage. Three things happened that could be culprits and I'm trying to narrow it down. First of all, I replaced my K&N filter with the stock filter a few months ago. I don't think that's a large part of the problem because I think I did a tank or two after that where I got almost the same amount of miles per tank. Right after that, it got really cold and the government mandated a larger percentage of gas be ethanol. I'd heard that ethanol led to worse gas mileage, but I didn't think it would be that bad. Is the extreme cold also part of the problem?

[jetwhine]

jubal,

The ethanol is the main culprit. I montitor my milage every fill up and since the cold weather and the blend change my milage has been 4-5 miles per gallon less than the summer blend. I also suspect that the oil companies will continue with this blend all year around so they can rape us of more money.

[jubal]

I thought it was mandated by the EPA.

[jetwhine]

jubal,

As far as I know which at times is not much, we have a summer blend and a winter blend. The winter blend being worse on gas millage. Lets hope they don't continue with that all year around.

[dandeman]

No question that the higher mix ethanol gasoline will cause mileage to drop......

What kind of mileage are you getting?

Another thing that will cause the mileage on 3rd gen runner to drop is a degraded front (ahead of the catalytic converter) O2 sensor..

Experience, and discussion with a trusted dealer service manager indicates you need to replace the front O2 sensor about every 75,000 miles. It's still working, but gradually operation is degraded by trace level contaminants in the gasoline.

Article: http://www.4x4wire.com/toyota/4Runner/tech/O2_Sensor/

One other thing that will kill O2 sensors is the use of any sealants containing silicone anywhere near the engine intake or gaskets on the engine (gasket sealant outgassing vapors will be sucked into the intake via the PCV system).. Silicone free gasket sealant has been available for quite a few years due to this..

O2 sensors are tricky enough in their operation that it's a bit of a risk to replace with an aftermarket sensor. Some do not have the right probe length and won't work properly.. If you ever replace it, get it from a Toyota dealer.