[qcj]

That might be true Michael, but I have no pump and I'm not having any problem with the AH or the dash heater not getting up to proper temp. I have changed my coolant and the large hoses and the 4 cut-off valves and run new hoses from the engine to the cut-off valves. The long hoses from the cut-off valves to the AH and to the dash heater I did not change. But these long hoses also run through heated compartments most of the way and the AH hoses are fairly short. Only two bays in front of drive wheels. After a days trip in cold weather the AH temp. gauge reads around 160 to 170 when we stop for the night. Not near as hot as it is when diesel is cut on, then it is 200 degrees, and on electric it will go to 210 degrees.
Don't get me wrong, I'm not saying you are not correct because you have been at this longer than I have. Merry Christmas