98 Dodge Caravan, 4cyl., heater problems


Old 09-27-09, 01:15 PM
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Join Date: Nov 2008
Location: Canada
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98 Dodge Caravan, 4cyl., heater problems

Hey Folks,

So, turn on engine, it warms up, I turn on defog or heater and hot air comes out for about 10 seconds as it gradually turns to cold air. Cold air remains coming out.

Shut off engine, restart, turn on defog...same thing, hot air for a short while, gradually turns to cold air.

I'm thinking thermostat stuck closed? Somebody told me it could be a sensor or something. Any ideas?

Why did they have to make cars more complicated with so many sensors?

Regards, Bill.
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Old 09-27-09, 01:27 PM
Gunguy45's Avatar
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Join Date: Dec 2007
Location: USA
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Just a guess..but I'd say its more likely a vacuum problem of some sort. The blend doors are probably closing after the initial vacuum from starting and warm up.

If you get warm initially then I doubt its the thermostat, do you have a gauge for water temp..or just a warning light?

JMHO...no expert
Old 09-27-09, 09:16 PM
Join Date: Sep 2009
Location: USA
Posts: 487
I think the blend doors are controlled by a cable but it may have a vacuum controlled water valve in the heater core inlet line. The cable could be loose too.

I'm thinking more of a clogged heater core that's only partially passing water. It'll get hot when no air is moving then when the air goes through it cools down.

Next time it happens can you feel the hoses on both sides of the heater core? They both should be hot.

Instead of shutting down the engine, just turn off the heat completely for a few minutes then turn it on again and see if it'll blow hot again.

I think you're looking at flushing, if not replacing, the heater core.

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