Apu not warming coolant for the truck.

Apu wont provide enough heat on its own to warm the coolant when it is that cold. Not unless you have a preheater or something on it. Bit like trying to warm your entire house with a small space heater. Not going to happen. At best it will likely boost the temps a bit from -15 to say 20 or 30.

 

You probably have 10-13+ gallons of coolant to heat. It would probably take several hours run time to bring the coolant temp up for the motor.

 

Assumeing it can even make enough heat in the first place. With it being that cold, even the ambient temps with the coolant pushed through the radators (1 truck 1 apu) from the pump is going to strip most/all of the heat out. I have a 5kw coolant heater and it will barely get my coolant to 80 degrees when its -15 out. And thats a dedicated heater.

Little apu trying to transfer heat?. Not a chance in bloody hell you get above sub freezeing temps.

 

That would be enough for me. Oil no longer molasses, and coolant in the high teens at least? My truck is starting!

 

Heating things from dead cold isn't going to happen. Keeping things warmed up a little after running has a better chance.

Your truck already has a block heater. Or it should. And hopefully it works. You'll just have to figure out the electricity part. Like a generator with 3 prong plugs and a extension cord.

 

How many watts is your block heater? How many watts does your inverter put out? What is the output of your APU?

IF the alternator has a 120 amp output, a conversion charts says that is 14,400 watts.

Make sure the inverter is rated enough watts to operate the block heater. Internet search shows Block heater varies from 750-2000 watts.