Really bad MPG since winter hit??

[JCL]

I seem to remember that the transmission does shift differently when cold, not due to traction but as part of the transmission control logic. It is related to the heat exchanger using engine coolant to warm the transmission fluid more quickly.

Also don't turn off DSC if you have sufficient throttle response to keep moving. If you are stuck and can't start, fine, but turn it back on as soon as you are in motion.

[JCL]

Originally Posted by racingbmwm3

would need to know the efficiency of the alternator, but let's say you have front and rear heated seats, each pulling 15amps at the high setting? ~200W/seat (@14V). ~800W total. If the alternator was 100% efficient, that is about 1.1HP. even assuming a horrible efficiency of the alternator of maybe 50%, that's 2HP.

Interesting calculation. I'd use 80% for the alternator, less 10% on the belt drive.

But if it means 1.5 hp, that is about 5% of the 30 or so hp required to maintain steady state cruising speeds. That's measurable.

[Junkycosmos]

In MN I can outright see the MPG difference in all of our cars as they switch the GAS from Summer to Winter. Winter fuel having more originators (sp?) but bottom line is those displace the denser gas, gas being higher in raw BTUs (BTU = energy). Sure there are theories about Winter gas burning cleaner but don't most computers in cars from 92 balance fuel burn factors?


In winter time our e39, X5, Sienna and MX5 all drop 10% right as the gas changes. During the summer time I have also played with buying ethanol free gas in the lightweight MX5 (4-cylinder) see an average of 10% higher MPG with ethanol free there too.

Agree on the prior postings too of tire pressure. Huge drops in tire pressure with the crazy low temps and is something often missed. (air pressure in a tire typically goes down 1-2 pounds for every 10 degrees of temperature change).

Interesting thought on extra electric draw during the winter but would that be offset by massive draw for A/C compressor in the summer?

As for transmission shifting: I have no idea on the transmission programs based on temp but I can tell you my 2005 @ 90k miles is shifting better after replacing my AT Transmission Thermostat (part 20 here RealOEM.com * BMW E53 X5 4.8is MOUNTING PARTS F RADIATOR ) Transmisison is appears to be warming up faster and shifts very smooth again once warm.


some other ideas here via google:
http://www.topspeedracer.com/better-...an-winter.html

[Junkycosmos]

speaking of MPG: I wonder how age of oxygen sensors might impact rich cycle warm up time or if this would be increased with older original OX sensors) ?

Anyone know reasonable way to accurately test response times ?

[Lexicon740iL]

I usually just fill my cars up and drive not really paying attention to my mileage other than what the OBC says.

On my last fill up I reset my trip meter after remembering this thread.

I can't believe it

I filled up with 92 octane Non Oxy 0% Ethanol on my last fill up.
24.xx gallons

292mi. before empty with 7mi. range left according to OBC

NOT COOL

[X5SND]

Gas what? You boys should be grateful to be getting what you are. If you
want to know "really bad gas mileage" come over to the range rover club. Just so happens The RRSS that sits next to the X averages between 10.9-11.3mpg for 'normal' (is it possible to drive 510hp economically?!) driving....if you're careful you can knock it into 12mpg but that's more work than fun. It works out to about $80 worth of go juice every 3 or 4 days on average. Seriously, when it's empty...fill it; and when it's cold, fill it some more! If you're MPG conscience don't buy a 5000+lb SAV. Bottom line.

Threads like this just make me chuckle.

[racingbmwm3]

Originally Posted by JCL

Interesting calculation. I'd use 80% for the alternator, less 10% on the belt drive.

But if it means 1.5 hp, that is about 5% of the 30 or so hp required to maintain steady state cruising speeds. That's measurable.

OK, for the 4.6is at 70mph and -5C (winter), I get 41.2HP including air drag and rolling resistance. I guessed .015 for winter tire rolling resistance and an optomistic 80% drivetrain efficiency. Have no idea what the engine efficiency is, so stuck with the default of .22, possibly higher on the 4.6?
Used this calculator: Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
And used 4.6is data from here: BMW X5 4.6is E53 (2001) - technical specifications - maximum power, maximum torque, fuel consumption - urban/extra urban/combined, maximum speed, acceleration, weight, dimensions, engine, suspension, rims/wheels, tyres, brakes, transmission/gear box,

Still, that's 3.5% going to just seat heating. I plugged in a parasitic load of 800W and it lowered the guesstimated gas mileage from 13.2 to 12.8mpg.

Interesting to see that the difference between -5C and +25C is 8HP because of the lesser air density and lower rolling resistance (summer vs winter tires).

[bcredliner]

Warning, Overload, hard drive full, too much information to process, drive less, don't check mileage in winter.

[JCL]

I used a SWAG (OK, some judgement involved) for my 30 hp figure. But I wasn't thinking 70 mph; the average on my vehicle over several years is closer to 36 mph, at which speed 30 hp may actually be pretty close. But then I don't have rear seat heaters. The only point was that the 5 or so % is another hit against mileage, added to increased idling time, less engine efficiency when cold, and all the other things that bring mileage down in winter.

What is surprising to me is that we have all these posters who didn't know that their mileage would drop when it got cold out. It has been doing so for the last 100 years or so.

BCR: You have to allow engineers to be engineers every now and then

[JCL]

racing: thanks for that calculator, it is interesting to play with.

I used the 4.6 vehicle figures (weight, cd, frontal area) at 5 c (my temp today) and pushed my average speed up to 40 mph, slightly higher than my average on my vehicle. The variables were:

Vehicle weight: 2180.9 kg / 4808 lbs
Crr: .012
Cd: .35
A: 2.8 m2 / 30 ft2
Fuel energy density (Wh/US gal.): 32970
Engine efficiency: .20
Drivetrain efficiency: .95
Parasitic overhead (Watts): 800
rho: 1.269 kg/m3

I got 11 hp total, lower than I had estimated. At 75 mph (hard to maintain that over a drive cycle) it was 43 hp.

I don't know if 800 watts is a reasonable figure, but taking it on faith I got 7.63 l/100 km and 8.38 l/100 km with an 800 kw parasitic load, at 40 mph, representing a 9.8% fuel consumption penalty for seat heaters on high. That is about double what I had estimated.