All glow plugs test a little below 1 ohm (when disconnected from the others). Plugs get voltage when the key is turned. I think they are OK.

Here is my new interesting update though: I left the car out in the cold the other night, no heater or charger, and started it the next morning. Probably low 20s overnight, maybe colder. One glow plug cycle and boom, fire and running. This is probably 7 hours later. OK.........

So, I leave it in a garage that day, overnight, with my new little magnetic heater on it. Come back and it won't start. Probably 24 hours later.

So, I am poking around under the hood and notice my secondary filter has lots of air in it..... I prime my stupid old leaky primer pump and nothing happens. I jiggle the filter and tilt it and fuel dribbles in it from the line. So, with fuel in it, I try again. One glow cycle and boom, it starts.

Fuel delivery: It's where I'm at now. I will try changing out both filters (I got 'em sitting on the shelf already, just in case kinda thing) and inspect all the fuel lines (especially the rubber ones that go into the tank).

Anything else I should look for here? This sounds like a VERY likely cause for the no-start.

And lastly, what relation might the cold have to this? Any?

__________________
'79 240D 4 speed manual 105k miles

That could be your problem.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Well, no fuel, no start. Leaking air into the system means lots of cranking to displace the air. The starter turning the engine over is the most inefficient fuel pump you can imagine. Thus the hand pump.

Check all the jumper hoses between injectors, the lines bringing fuel from the tank (there is a short, fat hose from the hard line from the tank that can get old and crack, and weep fuel/leak air), and your hand pump. Also check back at the rear of the car from the fuel tank, where there are a few other rubber lines subject to aging cracks.

The injection pump is a positive displacement pump. If you get air in it, it basically stops working correctly as it cannot generate the pressure needed to pop the injectors. The hand pump, while also not the most effective pump, is the designated device to clear the system of air. It is a piece of junk and has to be reasonably tightly screwed down. If it leaks fuel out, is will also allow air in. Not good.

There is an aftermarket hand pump that is less prone to leaking if yours is really the source of the problem. But be thorough when you inspect the vehicle. Until you get the system air/fuel tight, you will have difficulty as the starter is going to be worn out along with the battery performing this air purging task every time you start.

As for temperature contributing to the problem, the system is made of a bunch of dissimilar materials and they all have different expansion rates. The rubber O-rings in some places can handle this fine until they become aged and stiff. Cold O-rings are characteristically stiffer than warm ones.

So, make sure everything is sealed up. Sounds like you have done everything else. Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)