Quote:
Originally Posted by ecomodded
Most who drive a diesel notice mpg losses threw winter. Could the cold ambient outside air be responsible ? or has it nothing to do with cold air and more to do with winter mixed diesel.
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Diesel engines are more prone to the effects of cold winter temperatures because of they are more efficient than gassers. Greater efficiency -> less waste heat -> longer warm up time. Once the engine is up to temp it is still losing lots of heat to the freezing air flowing through the engine bay. Now, diesels like to run hot for efficiency, but keeping it hot in the freezing wind may be impossible.
My turbodiesel likes to stay around 78°C without the upper grille block. With the upper grille blocked, at temperatures slightly above freezing, the warm up process will plateu at 78°C, then go to 86-90°C after a longer acceleration or hill climb, and stay there. At the higher coolant temp the idle consumption is slightly lower (0.48-0.52 liters per hour vs. 0.50-0.54 lph). This last winter I had a cold start at below -18°C, no prewarming, and it took me twenty-something kilometers to get to 60-65°C. During the ~400km drive home the coolant temperature hardly ever got above 76-77°C, a 3km EOC would instantly cool it by at least 10°C. I told my passengers to keep their coats zipped and hats on, because trying to heat the cabin would bring the coolant temperature down to 70-74°C. In other words, even though I had both my grilles blocked and heating to the bare minimum (just enough to keep the windshield from icing over), the engine never got to its optimal operating temperature. Other than very low temps, driving conditions were ideal: sunny, dry, no wind, low traffic. Milage sucked on that trip.
Maybe the cold air going into my intake lowered my milage? On many occasions I've noticed that, even though it was cold (-10°C), by the time the intake air made its way around my engine bay (my filter box is behind the engine, so I have lots of prewarming before the air enters the turbo), its temperature was between 15-25°C
before the turbo, where the temp sensor is. I have no idea what the temperature was post-turbo and post-intercooler, but I seriously doubt it was lower than 25-35°C.
On the other hand, in the summer my pre-turbo temps can get up to 50°C, and the idle consumption doesn't get lower, even though the engine is hot (90-98°C).