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== Mechanical Troubleshooting ===== No Heat ===1. Check thermostat: Typically when the thermostat fails it is stuck in the closed position, causing the engine to overheat, making plenty of hot water available to the heater core. In some rare examples the thermostat can get stuck open, preventing the engine from reaching the normal operating temperature of [ 185 degrees F (need to verify temperature) ].2. Low on coolant: If there is insufficient coolant in the radiator you will likely notice an abnormally low reading on the dash gauge. In the event of a leak in the radiator, hoses, or part of the cooling system the level of coolant may fall below the point where there is sufficient liquid to circulate though the heater core.3. Heater valve: (need to verify fact: vacuum controlled valve with vacuum leak will not open and circulate coolant though heater core?)4. Clogged heater core: (need to verify) flush heater core one direction then the other. flush the cooling system using a back-flush kit. check dampers to ensure functional. (Does this truck have a vaccuum cut off valve?): Check the heater hoses that run to the heater core to determine if one is significantly warmer than the other.!warning! When attempting to disconnect hose from heater core, it is easy to damage the heater core by pulling too hard or twisting on the hose at the connection. Antifreeze sometimes causes the hose material to bond with the metal fitting making them extremely difficult to remove the hoses. Use care on the delicate heater core fitting.