taking a lot of cranking before diesel fires up
 

There is a lot of grey smoke before it finally starts up. Has been -35 to -40. Since end of December till now it sat and does not want to start up. Blows grey smoke and smoke rings, but does not start. Would this be a glow plug issue. Have never changed them and truck has over 200,000 miles on it. What should I check and if needed what are the best glow plugs to get?

Bosch Duratherm glows are what you want.

Might also try using the block heater anytime it gets below -10.

Thanks, I use both a block heater and I have another magnetic one that I put on the bottom of the oil pan at -25 Celsius. It has been starting, but taking way too long before igniting. I hadn't used it since a week before Xmas and it has been into the -45 Celsius range lately. Again, thanks a lot for the advice on part type as I know you prefer AC Delco parts most often.
UC Kid

zero weight synthetic is a big help in our climate for starting.

cold start
 

You may also want to try blending your fuel half tank #2 and half tank #1. Or if you are really having a hard time getting it going running straight #1 in extreme cold weather like you described wouldn't be a bad idea.

Thanks a lot you guys. I did buy 0 synthetic and a filter, but should have put it in a month ago. Have glow plugs coming and will change the oil at same time now that I have it in the shop and the weather is above 0 Celsius, odd for January, which is usually -35 or bouts. You mention blending #2 Zander #1 half and half. What do you mean by that, not following that.

#1 diesel fuel has a lower flash point than #2 diesel fuel. Meaning that the cylinder temperature can be lower and the diesel fuel will still ignite. The way I mix my fuel is that I run my truck down to half of a tank and fill up with the other fuel than last time. If I filled up with #2 last time that would mean filling up with #1 this time.