Heater won't get hot. Thermostat is ok diverter door works. What else do I check
Check the heater control valve.
And you may have air in the system that needs to bled out, or a plugged heater core. Make sure the engine gets to operating temp. of 195 to around 200* to insure a good thermostat.
be sure your coolant in the rad and expansion bottle is topped up
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