Quote:
Originally Posted by puddleglum
In winter, monitoring engine temp is important and the SG temp guage is much more accurate than most dash guages. If you engine isn't warmed up fully, you'll burn more fuel.
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I'm not sure that I like this suggestion. The big problems in winter efficiency are fuel blends, road conditions, and dense intake air.
That last one is killer for a couple of reasons, first, denser air means more fuel required to reach stoichiometric ratio, and the vehicle needs to burn at stoich to get the exhaust temps nec. for the cat to operate for emissions. Second, as any small plane pilot can tell you, peak performance soars, so you are throttling back more for the same performance. Throttling back creates vacuum, which means you are operating less efficiently.
A warmer engine can offset this a bit, but the efficiency change is not that great. The much bigger impact is rather or not the ECU has decided you are warm enough to run closed loop. If you are driving open loop in winter, the vehicle is generally pig rich, wasting fuel, and operating with less efficient emissions control.
This is why we are so focussed on more durable sensors and faster wideband measurement. So vehicles can get closed loop faster, and stay closed loop under greater loads.
From all the measurements I've seen, it would be better to make your driving decision based on rather or not the ECU is reporting closed loop operation yet, not a fixed temperature in, say, engine coolant. The problem with the later is that it will generally result in some needless idling, and, because of the extra fuel needed to achieve stoich, idling is more costly (efficiency wise) in winter.
-jjf