No heat when running, only when climbing a hill or stationary - KW T2000

Make sure heater hose valves are all open.

 

The engine runs hotter when under heavy load, but cool under normal load, sounds like you have thermostat that is sticking open.

 

Most trucks have some sort of valve on the heater hose lines between the engine and cab to shut off coolant flow to heater core inside the cab. The valves are normally either simple ball/lever valves or actual taps. With ball or lever type, when the handle is in-line with the hose it is open. Taps are just like your normal taps at home, turn to the left to open. The thermostat can't really be checked unless you remove it, but you can tell how it is working by how the coolant temp builds up. With the engine cold, start and run it for a few minutes, and then set it at about 1500 rpm and watch the temps increase. If it takes a really long time to get the temps up and they really do not get past 150 or so I would say it is stuck open. Normally the thermostat is closed to block coolant flow through the rad unit it is about 190 degrees. If it is working normally, you should see the temp gradually increase to about 180-190, then sharply drop 10 or so degrees as the thermostat opens and colder coolant from the rad is now pumping through the engine. If the thermostat is partially stuck open, as the engine is increasing in temp, so is the rad. You can feel the upper and lower rad hoses with your hand when the engine is around 140 or so and if the hoses are warm this means coolant is cycling through the rad when it shouldn't be.

 

The radiator needs to be full for the heater to work, might want to top it off.

 

You have a by pass issue that a check valve will fix in the shunt line. Any Cat Dealer can fix this.

 

also check heater door to see if its open that would be my guess it will still provide a bit of heat with thermostat open heater door or valve partially closed are most likely culprits

 

Your termostat is open...