It's going to be about 25 tonight and I just want to see if my block heater works. If I plug it in a 6 a.m. and start the truck about 6:55 a.m. is that enough time for it to do it's job?

 

Well, I never tracked temp increases over time, but I believe the consensus is that it takes about 3 hours for it to warm the coolant to its max temp.
So, I set my timer for 3 am and leave at 6- 6:30. I have never had trouble starting it without the block heater, but it does help it make heat faster on my relatively short drive to work. But I haven't experienced temps below the mid- to high teens in a long while around here. And even then not for more than a night or 2.

 

...Ditto,, what he said.....

 

Ditto, Ditto, two to three hours.

 

Glow plugs work? I have a couple in sequence that don't work, so I have to plug the truck in until I can find time to change them. Even without glow plugs working properly, 1/2 hour max on the block heater is all my truck needs to fire up. Just turn the key, let the glow plugs heat up once and you should be good to go. Even after 15 min of being plugged in, the plug for the heater will be quite warm, so you know there is a lot of juice going to that heater.

 

Yeah but your in Canada. It doesn't get cold in Canada!! LOL

Ok maybe it does.

I have always used a timer for 3 hours when I need a block heater. But less time does work.