My 99 f250 super duty ( 7.3 L Diesel ) seems to not want to start in this cold weather. I do plug it in at night, and am wondering if "heater " is not working. The batteries are new ( today ) and it turns over fine now but still hesitates to fire. The glow plugs seem to come on when key is turned to the prestart position. I am wondering if the plug to 110v or the heat element is not working. Anyone know where it is located and if you can feel "warm to the touch" when it is plugged in so I know it is actually working? let me know. Thanks.

I just did ball joints, steering gear box,
hydro boost, and universals with in the last month. Today I needed new batteries as the old ones from 5/08 had low charge issues and low cranking power with full charge. Now the rough starts. What next ?My wallet and patience are empty.

 

Most will tell you to change your oil to a 5w40 diesel rated Synthetic oil to help with the cranking speed, but i don't think it is needed, IMO.

GOOD batteries, Fuel that is not gelled, clean fuel filter, and a good Fuel additive to help the cetane rating all help starting in the cold.

So, to start with, change the batteries (you did, I read). Then change the oil, 15w40 is fine.
Add some Power Service Diesel 911 if you think the fuel is gelled. Change the Fuel Filter, and test your Glow plug relay / glow plugs. The relay is one of those things that you never thing about until it won't start in the cold. The relay can be bad, and still click when energized. To test, put a big screwdriver between the big posts for 15-20 seconds, then try to start. if it starts easier, you have a bad relay..... If it doesn't, start checking glow plugs.

You should hear some sizzling for a few seconds from the drivers wheelwell when you connect your block heater.

If after that you still have rough starts, I would start looking at other things.

Mine started yesterday in 17 degrees, took a lot more cranking, but started nonetheless. No block heater plugged in, no starting aids......