Temperature Vs Mileage - BMW Luxury Touring Community
 
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post #1 of 7 Old Oct 4th, 2011, 11:18 am Thread Starter
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Temperature Vs Mileage

Ok experts, would the ambient temperature of low 40's Vs low 70's cause a 5 MPG decrease?

Took a new job a month ago which has required me to drive 205 miles round trip each day for the last three weeks. My driving style and route have not changed but I have noticed the decrease in MPG as the weather cools off. I am not using any heated gear, nor the heated seat or grips.

Route is 65 miles interstate (set cruise 72-74 indicated on speedometer) and 40 miles two lane with around 5 miles of 30 - 45 MPH.

Running all 92 octane or higher.

TIA

Roy

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post #2 of 7 Old Oct 4th, 2011, 11:52 am
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Re: Temperature Vs Mileage

That's quite a reduction, but cold weather usually results in less fuel economy for several reasons.

- Cold air is thicker air. Thicker air needs a richer fuel mixture to maintain proper air/fuel mixture. Thicker air is also harder to push through.
- Cold temps make lubricants more viscous with more resistance (probably a wash after getting down the road 5 miles)
- Cold temps drop tire pressures (most of us will top the tires off), but also results in less heating so the tires don't increase in pressure as much as when it's warmer.
- Cold temps bring a change in fuel blends. Octane may not change, but the other properties of how the fuel atomizes and burns may change.
- Cold weather makes LT riders raise their windshield and deploy the air wings. More wind resistance.
- Cold weather increases engine warm up times. Engine runs in open loop longer with a richer mixture until normal operating temp is reached.

It's not one thing. It may not be all these things. It's a combination that will lead up to what we experience as less fuel economy.

Dave
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post #3 of 7 Old Oct 4th, 2011, 12:47 pm
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Re: Temperature Vs Mileage

My LT gets a little less mpg in cold weather. When I had carburated bikes seems like they did a little better in cold weather. At least they seemed to run a little better. But then again, that was a long time ago and it could just be my memory.

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post #4 of 7 Old Oct 4th, 2011, 2:52 pm
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Re: Temperature Vs Mileage

Best mileage is obtained in warmer temp. and higher altitude.

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post #5 of 7 Old Oct 4th, 2011, 3:15 pm
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Re: Temperature Vs Mileage

Also fuel formulations change with the seasons as well. Did you start buying fuel with ethanol in it? Did they add more ethanol to the fuel you were using? That will lower your mileage.

John
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post #6 of 7 Old Oct 4th, 2011, 3:57 pm
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Re: Temperature Vs Mileage

I suggest you check the operation of the engine cooling system thermostat and possibly the temperature sensor. With EFI engines the fuel/air mixture is richened based on a number of inputs, coolant temperature being one of them. If the thermostat is getting tired and not closing properly then it's possible that the engine is running cooler when the air is cold, hence a richer mixture may result. This being the case, in extreme conditions the engine may also begin to consume oil due to the richer mixture tending to cause washing of the oil from the cylinder walls. Larger EFI car engines are known for this, my Nissan RB30 engine being one case. Also, colder air is denser air, which means more oxygen (21% of total air volume) gets crammed into the cylinder, so there is potential to produce more power. Testament to this theory is the fact that diesel engines run better in foggy conditions. EFI systems require cold air, as much of it as possible, that's why there is no air preheat system and air intakes are set up to get as much cold air as possible. Preheating systems were required for carburettors, to prevent freezing due to high velocities through the venturi.

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post #7 of 7 Old Oct 5th, 2011, 8:23 am Thread Starter
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Re: Temperature Vs Mileage

Thanks Guys,
On the Ethanol question. It is next to impossible to find gas that isn't blended in this area. Who knows what blend you getting after it sits in their tanks...

Temp gauge is reading very close to where it reads in the summer so it appears the thermostat is functioning. Would suspect engine to run a little cooler with 45 degree air blowing on it Vs 70+ degree air.

Roy

Roy Gregersen

Ride Slow, Ride Fast, Always Ride Safe
85 K100RT sold
02 LTC DOA 9/21/14
12 R1200RT
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