<10mpg - wtf?

[Archangel]

My recent fuel consumptions, calculated trough dividing the miles traveled by the gallons needed to fill up: 9.86, 8.44, 11.48 I live about two miles or so from school, so the engine hardly ever gets warm enough to even open the thermostat. I haul 250lbs of shit in the trunk, all the time. When I worked for TRW I used to get over 14mpg all the time, even with the sand ballast. Is driving with cold engine affecting the ECM to the point it'll richen the mixture enough to drop my fuel economy by over 30%? Also, the 11.48 mpg was obtained while driving to Jackson and back, about 150 freeway miles both ways, wind chill temperatures of -10F - what the fuck is up with that, I was happily cruising at 65 all the time!!!

And last but no least - assuming I start up the car and let it idle, I can leave it running for over 15 minutes and it'll still be cold, the only way to get it to start warming up is to drive for a mile or so... Time for a new thermostat?

[88grandmarq]

cold weather usually reduces MPG, but shouldnt be 30% as you mentioned.
make sure the thermostat is working and not stuck open, most T-stats fail in the open position.
check for obvious vaccum leaks and check for stored trouble codes in the ECM.

[turbo2256b]

Cold will affect MPG. Short trips stop and go makes it worse. I averaged around 11 to 14 in town longer runs per tank. Now have only been running a few miles here and there MPG has been 6 to 9. Just not enough time for the engine to warm completly just 1 to 5 mile trips. Instant economy shows close to the same. Maybe not enough miles to get the average up.

[Tiggie]

That 15 minute warm up should be getting the car warm. Check to see if the coolant is flowing the radiator when you first start the car. But at 65mph with -10 temps, you'd have really cold heat if the thermo was stuck open.

Two-mile trips will kill MPG. I'll use 1/2 gallon of gas on a four mile trip, but after the first four miles, the MPG will start going up.

[Archangel]

Ah, okay then, so nothing out of the ordinary. I really don't think the thermostat is messed up as once I'm driving the car warms up just fine, and there's so much heat coming out of the vents I often have to keep the blower on its lowest speed.

I don't think there are any vacuum leaks, as the seems to be running just fine, plenty of power and all, no funky behavior. Guess I'll have to finally invest in a code-reader thing.

[packman]

Do you have a water temp guage? If so and the reading is low, couldn't you partially block the radiator with cardboard or something? I do that on my Chevelle and it keeps the temp guage around 180 degrees (195 degree T-stat) in this weather, and that's with a 4-core radiator.
Packman

[gadget73]

yeah, short trips suck for fuel economy. I normally can do about 16 on the highway, my around town is in the 8-9 mpg range. I work from home, and most of my trips are short jaunts to the bank, or to the sandwich shop around the corner, etc. Not enough to even open the thermostat. I can verify it on my car because I have a temp gauge in the manifold and one in the thermostat neck after the thermostat. The one on the dash wont even budge till the manifold gauge hits 190 or better.

[boXman]

My last tank was 11.5 mpg. :nonono: before that was 17, 15, 16, 14, 19....no highway.

[Lincolnmania]

it's the cold mang......i cant manage more than 15.1 mpg out of karens vic......the towny is in hibernation

[nitroracer]

My mileage in the probe drops from 27-28 on the highway to around 18-19 driving to and from school since its such a short drive and its 5* out. I think its going to be even worse on this tank.

[trife86]

Yea i noticed the other day im only gettin about 9-10mpg around town. i used to get a solid 13. i Dunno if its cause it needs a tune up or the cold

[turbo2256b]

One thing that affects warm up more than engine temp is rear gear lube. IF IT ISNT synthetiC it akes longer to warm it up than the engine. It is thick in the single didget range. You can pull the rear cover and it will just sit there.

[Nathan in MI]

One thing that affects warm up more than engine temp is rear gear lube. IF IT ISNT synthetiC it akes longer to warm it up than the engine. It is thick in the single didget range. You can pull the rear cover and it will just sit there.

:confused:

Explain, please?

[turbo2256b]

:confused:

Explain, please?

Cold does not affect synthic oil like dyno oil. Synthetic will flow at low temps dyno oil wont. An engine with dyno oil will be harder to crank at low tems. Thats with 10-40 or 10-30. Just imagine 140-90 wt oil in your engine. If its cold enough the engine wont even turn over. So there is your rear axle gears and stuff in there trying to rotate in oil thick enough you could roll a ball with it in your hand almost like silly putty.

[Nathan in MI]

Cold does not affect synthic oil like dyno oil. Synthetic will flow at low temps dyno oil wont. An engine with dyno oil will be harder to crank at low tems. Thats with 10-40 or 10-30. Just imagine 140-90 wt oil in your engine. If its cold enough the engine wont even turn over. So there is your rear axle gears and stuff in there trying to rotate in oil thick enough you could roll a ball with it in your hand almost like silly putty.

I understand that, but what does what's in the rear end have to do with warming the engine up?