Well its -40F here and my heater will not blow hot air. Engine temp comes up to 150 with my exhaust brake on. I had a cracked vacuum leak and fixed that. How much vacuum should a good pump give me in inches of water? Any other suggestions would be helpful. Thanks Doug

 

Is your coolant frozen in the heater hoses? I had that happen to a Camaro once at about -40 when I drove it down the highway before I warmed it up. I was young and stupid.....

 

I tested the coolant it was good to -50. Doug