Charon forgets Europe has extreme cold winters too, not just the US!
Nope - didn't forget at all. I have actually heard of places such as Scandinavia. I have also heard of Canada and Siberia.
It isn't only the fuel. Colder intake air results in lower compression temperatures, and cold engine parts don't help. Cold temperatures cause thicker crankcase oil and lower battery capacity, true for both compression- and spark-ignition engines. Far as I know most Diesels have some sort of cold start aid, such as manifold preheaters or glow plugs. Those depend on the vehicle battery, too, and if they pull the battery down enough the starter will have problems. My question remains - at what low temperature can a Diesel be reliably counted on to start?
There has been a lot of talk about how wonderful modern Diesels have become. Have they overcome problems with cold starting, such as zero F or about -20 C? Or even colder? Have they overcome problems with fuel gelling at temperatures below about 15 F (-10 C)?
When the temperatures drop drivers have to either put anti-gel additives in the fuel or make sure the fuel station has Winter Blend or #1 Diesel to avoid unpleasant surprises. When the temps drop much below freezing our school plugs in the block heaters on the Diesel buses.
What is the lowest temperature at which modern Diesels will start, unaided by anything other than on-board starting aids such as glow plugs?
Living in Scandinavia (although the weather seems more severe in parts of the US at the moment). Here we've had a few weeks of snow in total this winter and mostly temperatures above 0degC (ice age is coming to an end ) and I actually ride a bike to work since the beginning of January . Anyway from experience temperatures of -20 is no real problem starting from with most modern diesels although naturally an engine pre-heater is preferred in any car at that temperature. And we do have lots of them here.