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Old 05-19-2020, 06:13 PM   #23 (permalink)
Aero Wannabe
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Join Date: Dec 2007
Location: NW Colo
Posts: 629

TDi - '04 VW Golf
90 day: 51.75 mpg (US)
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Only drive your TDI in summer

To achieve the best mpg there are a host of reasons why winter driving is not your friend. We discussed several reasons why a fully warmed Diesel engine is much more efficient in a previous post.

1. If you must park in sub-freezing temperatures your engine, transmission and the whole drivetrain will be cold and inefficient. Park in a heated garage if possible.

2. Cold air is more dense. It is harder to push the car through denser air.

3. Daylight hours are shorter. You may spend more hours with the headlights on. (and wipers, front and rear defrosters, the heater fan has a large current draw and in some cars heated seats-not mine). Powering the alternator to supply all these accessories hurts mpg.

4. Snow tires. In another thread I was testing smooth wheel covers for mpg and changed from winter tires to summer tires on alloy rims as part of the testing. Tire and wheel weight, tread pattern and perhaps rubber compound killed mpg. Changing to summer tires gave much better mileage change than any wheel cover change I tested.

5. Winter blend fuels may affect mpg. I do not have hard data on this.

6. Even modern diesels start harder in sub-zero temperatures. On a ski trip this past winter I had to park outside a condo for a couple of days in very cold temperatures without being able to plug in my engine heater. I needed to move the car so I attempted to start it one afternoon. It took multiple tries but it finally started reluctantly and I left it running for a while to recharge the battery and warm the engine somewhat. Idling a cold engine is certainly not good for mpg.

7. Diesel engines do not “warm up” while idling like a gasoline engine does. With no throttle plate the engine is drawing in the same amount of frigid air as the same size gasoline engine would at wide open throttle, while injecting very little fuel. Drive gently and even climb a hill if you need to get heat into the cabin.
60 mpg hwy highest, 50+mpg lifetime
TDi=fast frugal fun

Originally Posted by freebeard View Post
The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.

Last edited by COcyclist; 05-19-2020 at 06:38 PM..
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