97 expedition warm heat on low heater core fine.coolant ok fan speed ok.seems higher fan speed the cooler the heat

SOURCE: 97 f 150 runs hot for minutes then runs ok

It could be a faulty thermostat. Did it do the same thing before u replaced the t-stat? It sounds like it's sticking closed, then all of a sudden it opens, coolant flows correctly. I'd consider changing it again. Check to make sure parts store is giving u the correct temperature thermostat also. Maybe it's too high for your Ford, delaying the opening.

SOURCE: 2001 Audi A4 2.8 no or little heat

there is a valvve that lets the coolant thru the heater core when heat is selcted then when it is off it goes thru thur the return instead of the heater core i bet your car is running a little off if it is the vavle works of a vacuum line and the vavle has a crack in it

SOURCE: 1999 ford expedition - transmission slip?

the flashing O/D light usually means you have a bad speed sensor that sends speed info to the engine & trans computer.

Vehicle Speed Sensor The vehicle speed sensor (VSS) (Figure 42) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.
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Vehicle Speed Sensor The vehicle speed sensor (VSS) (Figure 42) is a variable reluctance or Hall-effect sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.

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Some trans use an OSS, Output Shaft Sensor instead of a VSS. Depends on which trans you have, 4R100 or 4R70W

Transmission Control Switch (TCS) and Transmission Control Indicator Lamp (TCIL)
The transmission control switch (TCS) is a momentary contact switch. When the switch is pressed, a signal is sent to the powertrain control module (PCM) to allow automatic shifts from first through fourth gears or first through third gears only. The PCM energizes the transmission control indicator lamp (TCIL) when the switch is off.

The TCIL indicates overdrive cancel mode activated (lamp on) and electronic pressure control (EPC) circuit shorted (lamp flashing) or monitored sensor failure.

Output Shaft Speed (OSS) Sensor
The output shaft speed (OSS) sensor is a magnetic pickup, located at the output shaft ring gear, that sends a signal to the powertrain control module (PCM) to indicate transmission output shaft speed. The OSS is used for torque converter clutch control, shift scheduling and to determine electronic pressure control.

SOURCE: At idle, Heater Core Return Line is flowing only

two things--first replace your cabin air filter.second reverse flush your heater core with a garden hose and that should remove the build up of material in your heater core and restore the flow,hope this helps

Testimonial: "Hello; I backflushed heater core, cooling system flush. Heater floor vent temp. went from 96 degrees to 140; Thanks for your excellent advice. Robert"

SOURCE: 2004 Chevy Impala no heat. Fan OK. Engine warms

Your heater core is clogged. You can fix it. Disconnect the two heater hoses and put one into a bucket. Use an air compressor to blow into the other - it'll flush the contents into the bucket. Then reverse it - put the hose you blew into, in the bucket, and blow into the one that was in the bucket. This way, whichever side of the core had the clog, you can blow it out. Reconnect the heater hoses, and then burp the system or you can end up with air bubbles in the cooling system that can cause you to overheat. Click my screenname, go to Tips and Tricks, and follow the procedure there - it'll walk you through the whole procedure step by step.