I may be missing something simple but, I have no heat on my 88' F150. Last night I was playing with it and in the evening I would get some heat but not enough to make you warm. Later at night it just blew cool air. I have flushed the system and it hasn't changed ( had the heat on for the flush). Its 20 miles to the nearest parts store so I want to have a good direction before I head to town. Thanks

 

Most common reason would be a thermostat that is stuck open.

With a cold engine, start it and feel the radiator hose that supplies coolant to the radiator. Also monitor the heater hoses.

A normal warmup cycle should cause both heater hoses to warm up before the radiator hose gets warm. The radiator hose should only get hot after the engine reaches operating temp (about 180-200 F).

If the thermostat is stuck open, the radiator hose will get warm as the engine warms up. Unfortunately, this will keep the engine running cold and will keep hot coolant from circulating through the core.

If the radiator hose appears to be normal, compare the heater hoses for temperature. If one is hot and the other is cold, the core is clogged.

Make sure the pump is movng coolant.

What does your temp guage do?

Steve