how long for heat

If you're idling, it shouldn't take that long. Check your coolant levels.

If you're driving, you may need a winter front.

 

new thermostat

 

That's a looooooooooooooong time. If I have mine plugged in, I have heat in less than a minute. If not, about 5-10 min.

 

Thermostat(s) or crud build up

 

Same deal here. 2004 KW T2000 / Cummins ISX 475. Good coolant levels, PM'ed monthly, but takes 30+ minutes to give me any heat on recent cold mornings (-5 degrees, truck plugged in). I reckon it's just the thermostat stuck open. Once I drive it for 10 minutes it gets up to normal range.

 

1999 KW W900L Detroit..
New thermostats, winter front and full of LL coolant.
At least 20-25 mins idling before I get any useful heat when the temp is 25 or below.

...however, once the heat starts - it gets to be a sauna in there. I almost have to shut it off.

 

My 05 ISx, and all of our late 90,, model cummins and detriot's take at least 30 plus minutes to warm up, enough to blow any heat. Even if they are plugged up.

 

I think 12 gallons of coolant takes time to warm up!

 

Sounds like a job for a webasto coolant pre-heater!