Diesel fuel economy: No reduction in the winter?
Thread Starter
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Joined: Apr 2004
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From: N. Illinois, USA
2021 GLS450, 2015 E250BT 4Matic, 2007 GL320CDI, 2005 SLK350, 2001 SLK320
Diesel fuel economy: No reduction in the winter?
The 2007 GL320 is my first diesel-powered vehicle, so I'm learning a few unique things about diesels. Like, for example, the fuel economy on my GL320 has not dropped at all during the cold weather. 
Every gas-powered car I've ever driven has suffered a 10% to 15% drop in fuel economy in the winter. My GL320 has maintained the same MPG even as temps have dropped into the teens.
Question: Is it common for diesels to maintain the same MPG despite colder outside temperatures?
If yes, then why aren't diesel engines bothered by cold weather?
Obviously, I'm not complaining, just curious!
Every gas-powered car I've ever driven has suffered a 10% to 15% drop in fuel economy in the winter. My GL320 has maintained the same MPG even as temps have dropped into the teens.Question: Is it common for diesels to maintain the same MPG despite colder outside temperatures?
If yes, then why aren't diesel engines bothered by cold weather?
Obviously, I'm not complaining, just curious!
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From: Albuquerque
'10 CL550, '12 GL550
One reason you've experienced gasoline fuel economy drop in winter is due to mixing ethanol in.
This isn't done with diesel.
In addition, the gasoline engine runs on "choke," i.e. cold start injector for longer time when engine is cold. No equivalent system exists--or is needed--on a diesel.
This isn't done with diesel.
In addition, the gasoline engine runs on "choke," i.e. cold start injector for longer time when engine is cold. No equivalent system exists--or is needed--on a diesel.
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From: Spicewood, TX
2008 GL 320, 2007 Silverado LTZ C3500 Duramax Turbo Diesel
It is pretty common for diesels to have a C.A.P. system (Cold Ambient Protection) for when the air temp is below freezing and the coolant is below a certain temperature. I wasn't aware that the GL 320 had this until this morning, the first good freeze this year. As soon as she started it and backed out of the garage, the engine RPM came up significantly, as it idled for a few minutes.
All of my previous Powerstrokes had it and now my Duramax has it. I usually notice significantly better fuel mileage in the winter due to less AC. I don't think the air temperature itself has much to do with it.
All of my previous Powerstrokes had it and now my Duramax has it. I usually notice significantly better fuel mileage in the winter due to less AC. I don't think the air temperature itself has much to do with it.
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From: Federal Heights, CO
1982 300D VNT, 1980 240D 3.0T, 1982 300TD
Diesels usually get slightly less (1-3mpg) in the winter due to Kerosene being mixed in to prevent gelling (Called D1). The change happens around October/November for most states. They get less MPG because Kerosene has less energy per gallon than Diesel (D2).
The GL probably does not notice because it is so efficient and/or the reduced A/C usage evens out the MPG.
The GL probably does not notice because it is so efficient and/or the reduced A/C usage evens out the MPG.
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From: Albuquerque
'10 CL550, '12 GL550
Mine basically starts at 1400 rpm when cold.
I warm mine up by driving it off, gently of course. Might as well get some motion out of the fast running.
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From: Spicewood, TX
2008 GL 320, 2007 Silverado LTZ C3500 Duramax Turbo Diesel
That's good information.
It must be an either/or for air temp/coolant temp because on all of my T444E's (7.3L Powerstroke) the CAP system initiated on all cold mornings and it very rarely gets to 14 degrees in Austin, TX.
It must be an either/or for air temp/coolant temp because on all of my T444E's (7.3L Powerstroke) the CAP system initiated on all cold mornings and it very rarely gets to 14 degrees in Austin, TX.
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Thread Starter
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Joined: Apr 2004
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From: N. Illinois, USA
2021 GLS450, 2015 E250BT 4Matic, 2007 GL320CDI, 2005 SLK350, 2001 SLK320
I'm getting a consistent 20-22 in stop/go suburban driving on level terrain. Highway is 25-26 depending on wind speed/direction. I've gotten as high as 27.5 on the highway.
Also, thanks everyone, for the responses on the winter fuel economy. I didn't know about the CAP system but it looks like a good thing to have in the winter.
Also, thanks everyone, for the responses on the winter fuel economy. I didn't know about the CAP system but it looks like a good thing to have in the winter.
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From: Blaine, WA
07 E320 Bluetec
Diesels usually get slightly less (1-3mpg) in the winter due to Kerosene being mixed in to prevent gelling (Called D1). The change happens around October/November for most states. They get less MPG because Kerosene has less energy per gallon than Diesel (D2).
The GL probably does not notice because it is so efficient and/or the reduced A/C usage evens out the MPG.
The GL probably does not notice because it is so efficient and/or the reduced A/C usage evens out the MPG.
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From: Toronto
2006 E320 CDi, 2008 3/4 Ton Suburban, 2007 "rice rickshaw" Accord 5 speed
My 3/4 ton sweet heart!
I'm getting a consistent 20-22 in stop/go suburban driving on level terrain. Highway is 25-26 depending on wind speed/direction. I've gotten as high as 27.5 on the highway.
Also, thanks everyone, for the responses on the winter fuel economy. I didn't know about the CAP system but it looks like a good thing to have in the winter.
Also, thanks everyone, for the responses on the winter fuel economy. I didn't know about the CAP system but it looks like a good thing to have in the winter.
It has only 90 km or 54 miles on the clock and it already pulls like a locomotive. The brochure says to expect a reduction of 1 mpg. With a 39 gallon (US) tank it is not a worry.
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From: Toronto
2006 E320 CDi, 2008 3/4 Ton Suburban, 2007 "rice rickshaw" Accord 5 speed
America the Brave (and Beautiful?)
There are more:
Rear leaf spring suspension, 8 lug wheels, leather captain chairs, rear view camera in the NAV system, satellite radio, full heavy duty hydroformed frame, 3.73 ratio, built in the Lone Star State, country of the Texas Cadillac.
She is a beauty! Better still she burns a lot of unleaded. It is a great pity the Duramax-Allison package is not available in the Suburban.
It is an even greater pity that neither MB nor the Japanese built such machines tailored for pounding North American roads.
Rear leaf spring suspension, 8 lug wheels, leather captain chairs, rear view camera in the NAV system, satellite radio, full heavy duty hydroformed frame, 3.73 ratio, built in the Lone Star State, country of the Texas Cadillac.
She is a beauty! Better still she burns a lot of unleaded. It is a great pity the Duramax-Allison package is not available in the Suburban.
It is an even greater pity that neither MB nor the Japanese built such machines tailored for pounding North American roads.
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From: Spicewood, TX
2008 GL 320, 2007 Silverado LTZ C3500 Duramax Turbo Diesel
..............or like the Excursion we sold when we bought the GL 320. 7.3L Powerstroke, 4 x 4, 7400 lbs, 17 mpg, and could haul a whole soccer team or pull anything that was trailerable (is that a word?)
It had a mere 92K miles on it and had never seen the mechanics shop except for a minor re-call issue with the wipers. Some lucky person will be driving that baby for a long, long time. If I had room in my garage, I would not have sold it, since it was the lasy MY with the 7.3L.
It had a mere 92K miles on it and had never seen the mechanics shop except for a minor re-call issue with the wipers. Some lucky person will be driving that baby for a long, long time. If I had room in my garage, I would not have sold it, since it was the lasy MY with the 7.3L.
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From: Albuquerque
'10 CL550, '12 GL550
