Substancial decrease in gas mileage lately

[BSOD2600]

Over the past month, I've noticed my highway MPG go from ~23 down to 18 MPG when I filled up tonight. I've noticed it slowly go down over the past month too in general. Several years ago, this was the sign that my engine was dying (ended up not having compression in a cylinder). My driving style hasn't changed, nor the route to/from work, etc.

Anyways, I've read about the gas companies changing the fuel mixture from summer to winter, which helps/changes how easily it vaporizes, etc can can effect mileage. Do you think this is what I'm seeing? The PNW has gotten colder in the last month, that's for sure.

Thoughts?

[ericem]

Colder means it needs to run more rich technically though. Try some injection cleaner anyway. Replaced the O2 sensor before?

[DLC]

I got lower economy last tank, and I'm going to see if the trend continues as it has most winters in that regard.

[BSOD2600]

Replaced the O2 sensor before?

Not on this engine. Really would like to monitor it with a select monitor (or insert others), but don't have access to one, before I spending the ~$100 on willy-nilly replacing it.

I'll continue to monitor it over the next few tanks and see how it progresses.

[RJ93SS]

it's cause you guys have shitty gas down there, could it have to do with colder intake temps, that should raise mileage though should it not?

[Dynamic Entry]

and our gas is better?

I can't even find higher than 91 Octane in Calgary. That's Calgary Alberta, home to multinational oil companies Head Offices!!!!!!!!!!

sorry about the rant.

interesting thread, I didn't realize fuel changed from summer to winter. I learn all the time.

[RJ93SS]

multinational as in it's all owned by texans.

i have never heard anybody say our gas is worse, and in vancouver we have 94 octane at most gas stations. my car runs way better on 94 octane cdn gas then any high octane american gas, however, american gas is about 40 cents a litre cheaper than ours.

[94SS_Canada]

Tell me about it, im lucky to have a Gas station down the street from me that carries 91, but thats it. Whenever im in Calgary i barely see anything higher than 91 as well..

[Adam West]

I recently had a horrible run of mileage - thought the car was running rich, smelled like I was running catless and guess what? I had a leak in my fuel line...gas leaking out on the ground.

But yes, my car is running richer in the cold weather.

[dscoobydoo]

October to Feb, the stations switch to higher ethanol blend.

[RJ93SS]

so up in canada, we have this mohawk gas that contains 10% ethanol, should i not be using this even if it's 94? what kind of effects would this have on our turbos... more heat or less heat?

[biggreen96]

RJ93 - I have been using 94 & 93 octane exclusively in my wagon for the last 4 years. It's also a 10% ethanol blend, and I haven't had issues. I'm not stock, and I do use the car vigorously. No heat issues to report.

[Legacy777]

There was a similar gasoline quality thread on nasioc. There's a few things I feel need clarified.

Gasoline is gasoline as long as it's the same grade. It doesn't matter who you get it from, etc. The main difference between stations is the additive package. Beyond that, there are different grades of gasoline. High vapor pressure, low vapor pressure, and sub-grade are to just name the primary ones.

Low vapor pressure gasoline is sold in the summer months to reduce evaporation. This page has a pretty decent article on vapor pressure.

http://fuelfocus.nrcan.gc.ca/issues/200 ... ment_e.cfm

During the winter months in some areas, and all year round in others, an oxygenate, typically 10% ethanol is added to gasoline to help promote complete combustion.

10% ethanol may drop your mileage 10-20%. The vapor pressure change in gasoline shouldn't affect mileage or drivability in a fuel injected vehicle.

One last point, ethanol will raise your ocatane level. So if you add 10% ethanol to a premium 91 octane, you may have a blended final octane level that's higher then the base gasoline octane rating.

Alternatively, what some suppliers are doing is using sub-grade octane gasoline that have octane levels lower then 87, and then blending them with ethanol and/or premium to get a final desired octane rating. I would say this practice may be most common where 10% ethanol is used year round. They will use sub-grade gasoline, and blend in the ethanol to get the 87 octane.


Also, you car shouldn't be running any leaner or richer in colder weather then warmer weather. That is why you have a MASS air flow sensor. The air may be colder and more dense, which will call for more fuel to maintain the same AFR's, however you will also be getting more power. So to say your car is running rich because of cold weather is not true.

[93Leg-c]

Hmmm, both Dave (DLC) and Josh (Legacy777) say gas mileage goes down in the winter. I've consistently gotten the opposite results. As soon as summer gas mixture is used in my car, the mileage goes down to 20.5-21.5 mpg with very noticeable drop in power. When the winter gas mixutre is used, gas mileage goes back up to 24-25 mpg with a very noticeable increase in power.

[kimokalihi]

I believe it could be the temps or winter gas. In my 98 chevy metro I installed a ScanGaugeII and I watch my gas milage all the time. What I've learned is that I get like 10mpg less at night than I did during the day about a month ago. It was around 65-70 on my way to work and I'd get high 50s doing 55mph. On my way home at night it was more like 45-50 and I was getting 39-40mpg.

Now that's it's getting dark a lot earlier and it's dark by the time I go to work I get the same milage both ways but it's gone down even more now that it's started to get colder out. 35-45 range. I'm averaging 36mpg now. At 55mph on straight level stretches I get between 36-38 and my last tank was 36.7 last night. When I got the gauge I was getting 42-44 mpg in the summer.

I'm almost positive it's the colder temps that kill your milage. I think it's denser causing the car to add more fuel and the added performance is outweighed by the fuel consumption and your fuel economy goes to hell.

I also saw on some metro site that a guy rerouted his intake to pull air right off the exhaust manifold and claimed he saw an increase in MPG from doing so. I should try that and see if my fuel economy goes up...

[BSOD2600]

Well since my initial posting, the next two tanks of gas I've gotten 20 and 22 mpg. Still slighly lower then my ~23 mpg average, but at least not continuing the crappy 18mpg trend I saw. Been filling up at different stations/cities each time so can't narrow it down to a specific place/brand atm.