Heater Cores and Blower Fans
Mazda MPV
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Mazda MPV Heater doesn't work coolent level fine temp knob doesn't change temp but does change air velocity heater core hoses are only slightly different temps any ideas?

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Answer

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05/10/2013

Answer - Coolant not flowing to heater

This sounds like the heater core is clogged, the heater hose is clogged, or the heater supply valve is not allowing the heated coolant to flow to the heater core.

Answer

In addition to the above, the thermostat may be stuck open and need replacing.

Additional info:

Are you checking the coolant level at the radiator or at the overflow tank? You need to check the cooling system, not the overflow tank.

If you recently changed your coolant, you may have air trapped in the cooling system. You'll need to rev the engine up and force the air out of the system. You may need to rev the engine pretty high.