gas mileage really droppin

SilverFox90 · Dec 21, 2004

my gas mileage has dropped from like 200 miles a tank to now i have only 120miles on this tank and have used over 3/4 tank

jpctln · Dec 21, 2004

Welcome to the club. I only get about 15-16mpg now.

HISSIN50 · Dec 21, 2004

what does this equate to in MPG (per calculations done upon filling up)?
that is the only way to really figure out what gives, IMHO.

good luck.

MusPuppis · Dec 21, 2004

Gonna be watching this thread.. I put a half tank in my truck and Ive used a 1/4 tank up already and gone about 35 miles. Something is very wrong with that.

HISSIN50 · Dec 21, 2004

it sometimes happens this time of year. some folks have trouble staying in C-L and parts of the country have blended fuels.

SilverFox90 · Dec 23, 2004

well basically it has gone from 15mpg to about 10-11mpg its been cold lately but thats a big drop fuel filter?

JamesB88 · Dec 23, 2004

I only get 7mpg from what i fiqure, Ive heard Vac. hoses could be leaking and causing bad gas mailage. James

Michael Yount · Dec 23, 2004

Lots of stuff in the winter conspires to reduce mileage. The fuels are blended to make for easier starting - they have less btu content which results in more fuel being used to generate the same power. The cold air is more dense - takes more power to push your car through it. Tire pressure drops with temp - most people don't catch it for a while - low tire pressure reduces mileage. A lot of people crank their cars and let them idle to warm up or just spend more time warming up before driving - lower mileage there. If you're dealing with inclement weather - traffic is usually heavier, and you're going much slower - more stop and go - worse mileage there. Colder oil is much more viscous - takes more parasitic power to run the engine til the oil warms up; and even then, it's probably running cooler than it otherwise would - more loss there. Same with coolant temps - the engine usually runs a bit cooler - hotter (up to a point) allows the engine to get better mileage. Note - that's hotter operating temp, not hotter intake air.

Add two or three of those things together and you can notice a significant drop in mileage. The good news is the engine loves the colder intake air....

Michael Yount · Dec 23, 2004

Most important part - having said all that - pull your codes and see if something's wrong. A problem with O2 sensors or the temp sensors (ACT or ECT) can contribute to poor mileage. If the O2's have more than 50K on them, you probably ought to replace them anyway - you know, kind of like replacing plugs and filters regularly. The O2 sensors performance degrades over time.

jaidedeye · Dec 23, 2004

having the same problems bud,

i think its the cold weather...my car was not warming up enough...it would only go to 150 ish when it was 20-30 degrees out.found out i had a 160 thermostat in my car.......could be my 18 inch flex fan spinning all the time.....run codes and check all your sensors like michael said. if its cold, try to cover up half your radiator with cardboard or something....yeah i know its ghetto but it might help if your weather is playing havoc with your fuel economy like mine is.

crunchie12268 · Dec 23, 2004

I do too, but I think it is because I take advantage of the cooler air

jrichker · Dec 23, 2004

Dump the codes and see what the computer says is wrong…

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great.

See http://www.troublecodes.net/Ford/
OR
See http://www.dalidesign.com/hbook/eectest.html for more descriptive help
OR
See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html

IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Walmart.

Michael Yount · Dec 23, 2004

Ran a little test today boys. Drove from K'ville TN to Augusta GA through Atlanta. The rolling terrain is pretty much the same for the whole trip. The traffic was pretty much the same for the whole trip. Small change in wind direction, but it actually hurt me during the second half. Because of a cold front passing through I had a big temperature difference for the first and second parts of the trip. I used the trip computer on my wife's Bimmer to keep track of mileages. The first 200 miles or so it was between 25-30F. We averaged about 35.1 mpg. The last 150 miles of the trip the temp. jumped up from 45F-55F. We averaged 37.1 mpg for that leg. Speeds on both legs - on the cruise control - about 75 mph. The only significant difference was the temperature. I even stopped around 200 miles and topped the tank back up so the fuel load was about the same - although that was only about a 40-50 lb. variable.

That cold dense air takes more umph to push the car through - that's how it shows up at speed. Less difference due to aero drag would show up around town.

Not scientific - but I limited as many variables as I could - and the results were interesting.

jwzg · Dec 23, 2004

Yount, pleeeeease don't tell me you were in the V8 Volvo, because if you say you were, this is the first time I'll throw the flag on you.

Edit: Wheew, I didn't see the phrase about the Bimmer. Man, I thought I was going crazy there for a minute.

HISSIN50 · Dec 23, 2004

Michael, for Christmas i should get you an anemometer so you can be a 'little' more precise with your testing.

seriously, great test, great info. you should be focusing on holiday festivities though.

Michael Yount · Dec 23, 2004

jwzg - read the post more carefully - you'll see this line "I used the trip computer on my wife's Bimmer to keep track of mileages". We were in her car.

The best single tank the volvo has knocked down was 26.8 mpg at about 65 mph on I75 in Ohio last fall. Best overall trip average was 26.3 mpg on a 520 mile roundtrip between Knoxville and Bowling Green for Corral Day this past July. I just filled it up before leaving town (full tanks = little condensation) - around town tank averaged 19.3 mpg. Throw the flag if you must - all mileages are true.

Wife's car is powered by a 1.9L DOHC 4 valve 4 banger - smoothest 4 cyl. in existance in my humble opinion. Amazing to me how it knocks down 35-40 mpg while zipping along at 75mph and 3700 rpm!

JT - I was concentrating on the holiday prep- driving the car/wife/presents to the in-laws!! Only had to push a couple of buttons to keep track of the mileage.

Enjoy the weekend guys!

85_SS_302_Coupe · Dec 23, 2004

I think a lot of it has to do with the afore mentioned cold air and the fact that the colder the intake air is, the more spark it takes to burn fuel. EFI has the great ability to do what it needs to correct what it can but it's not perfect. I know at least my car being carbed, and since i don't rejet my carb for winter because i only drive it once or twice, it runs like poop and gets junk mileage.

Michael Yount · Dec 23, 2004

85SS - the engine LOVES cold intake air; it's pure thermodynamics baby; ignition system should have plenty of spark for warm or cold. The bigger 'delta T' (temp diff.) the more HP can be generated. For each 10F drop in intake air temp, the engine makes 1% more HP -- assuming of course you have the capability to provide the extra fuel. EFI/mass air motors adjust for all that automatically. The MAF registers a bigger mass of air flowing in at w.o.t. because of the denser cold air - and voila - more HP. As you point out, carbs don't tend to deal with the environmental changes as well or easily - one of the reasons they've gone by the wayside on newer cars.

jwzg · Dec 24, 2004

Read the edited part, Mike. I edited it right after I wrote the post. I left the first part in there so we could all have a little laugh at my expense.

HISSIN50 · Dec 24, 2004

Michael Yount said:
JT - I was concentrating on the holiday prep- driving the car/wife/presents to the in-laws!! Only had to push a couple of buttons to keep track of the mileage.

Enjoy the weekend guys!

Yount clan, you too!

FWIW, i did not literally mean concentrating on the road. LOL. i meant that the analytical Guru could try to not perform experiments during a time of relaxation and family gatherings (said in-cheek - i know you do those calc's all the time anyways).

Happy Holidays!

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