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Heater blows hot at idle and cold when driving

Have a 2002 mazda mpv diesel and after a fast idle of 2000-2500rpm the front and rear heater blow hot air but when you start driving the car the air goes cold and will not go hot until you stop and fast idle again

Posted by michael normandale on

  • michael normandale Jan 09, 2014

    have replaced thermosat and flushed water threw rad and heater with a hose pipe have also replaced the engine temp sensor

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Colin Stickland

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  • Cars & Trucks Master
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The water pump impeller has come adrift from the drive shaft ,one is plastic and and the other metal and they come apart causing this sort of problem

Posted on Jan 09, 2014

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motor1258

Mike Butler

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SOURCE: 2002 caravan, heater problems

That was a common complaint a few years back, due to the fact that the heater core is a little too much higher than the engine, which requires that extra push it gets when engine RPM's increase. One thing I did do on my Caravan was remove my hoses to the heater core, and use a small external pump with hoses to circulate C.L.R. through my core for a while, then let it sit with CLR in the core overnight.Next day I circulated it through again, both ways by reversing hoses, and then re-attached hoses, bled air out of system, and notice quite an improvement in heat at idle. Once cleaned out, the heater core allowed coolant flow through it better at idle. If your stumped by explanation, take it to an automotive shop, or a Rad shop, and get a quote on flushing that core out for you. I recommend the CLR, but it might be too time consuming for you , but a flush will probably show some noticeable improvement.

Posted on Nov 23, 2008

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Anonymous

  • 251 Answers

SOURCE: 2006 chvy impala when idling dont blow hot air

1 Inspect Cooling System Mix Coolant level low or flow is restricted. grey_line.gif 2 Inspect Thermostat Thermostat stuck closed grey_line.gif 3 Inspect Heater Control Valve Leaking or defective heater control valve. here something to help u

Here to help Shaun

Posted on Nov 23, 2008

Anonymous

  • 405 Answers

SOURCE: After car heats up (slow to heat) it stil blows cold until moving

http://www.fixya.com/cars/t1386554-91_ford If this doesn't help you tell me more, if it does, please vote me fixya, otherwise please do not give me any rating at all, the only compensation I get is my Fixya score, Merry Christmas.

Posted on Dec 22, 2008

Anonymous

  • 1 Answer

SOURCE: Heater blows cold air when idle

Sounds like you may have a partially plugged heater core. You could flush this out separately, from flushing radiator & engine block. Diconnect heater hoses going to your heater core and clamp off, so not to loose coolant from engine. Now hook up separate hose to one side of heater core pipe and flush out with typical garden hose. Repeat procedure on both heater core inlets. Reconnect original heater hoses and test difference. You may have to add an additional litre of antifreeze. If this don't work i suggest changing heater core. Good luck.........Ron.

Posted on Jan 03, 2009

Curt Downs

  • 1779 Answers

SOURCE: 2001 Dodge Caravan heater blows cold air when stopped

Have you checked the coolant level? What you describe is exactly what happens if the coolant level is low. When stopped at idle, hot coolant is not circulating through the heater core, so no heat. As the engine increases in rpm's when you pull away from the light, the water pump is spinning quicker, and some coolant is making it to the heater core. So check the level, and if it is low, keep an eye on it to see if it drops again. That of course indicates a leak somewhere. Get it fixed, as overheating the engine leads to costly repairs and worse case a new engine. Let me know how you make out with this.

Posted on Dec 05, 2009

Testimonial: "Thanks Curt! You were right ON!"

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