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Discussion Starter · #1 ·
At the in-laws for Thanksgiving and father-in-law's 98 Grand Caravan with 276k is having trouble with the heater.

Symptoms: will not blow heat until quite a ways down the road, long after the engine temperature has come up.

Blows cool or only luke-warm air at idle once warmed up, as soon as you drive or rev the engine it will heat again.

Coolant is full, no overheating issues and no leaks that I can see. When you move the dual temp controls back and forth you can hear the changes from the blend doors and it will switch from cold to hot air just fine (when driving).

Any ideas as to what could be causing the long wait for heat and why it goes cool when idling?

I am thinking maybe the water pump is on the way out...
 

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Virginia Gentleman
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I'd suspect the heater core - it may be partially plugged resulting in poor heat. Water pumps usually start to weep as the seal begins to let go. Check the weep hole.
 

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Take the hoses off that go to the heater core and flush it thoroughly both directions. Also check the water valve. Make sure it is working and fully open for heat.
 
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Virginia Gentleman
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A good flush should loosen any crud that has built up in the heater core. Reverse flushing the heater core will help. Refill with the proper 50/50 mix of HOAT (Zerex G05).
 

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Is the rad full or are you going by the recovery bottle?
Full bottle doesn't mean full rad.
 

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Discussion Starter · #6 ·
Update: I went with what FIL told me as to the radiator being full of coolant...

He took the cap off and looked one day and said it looked to be about an inch or two down...

We managed to put about 3 quarts in the radiator and another couple quarts in the recovery bottle to get it between min and max level.

Now that it is full of coolant and has gone through a couple heat and cool cycles the heat works just fine.

Thank you all for the ideas and suggestions. Looks like next summer we will need to replace or bypass rear heater coolant lines, the corrosion is getting bad.
 

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Update: I went with what FIL told me as to the radiator being full of coolant...

He took the cap off and looked one day and said it looked to be about an inch or two down...

We managed to put about 3 quarts in the radiator and another couple quarts in the recovery bottle to get it between min and max level.

Now that it is full of coolant and has gone through a couple heat and cool cycles the heat works just fine.

Thank you all for the ideas and suggestions. Looks like next summer we will need to replace or bypass rear heater coolant lines, the corrosion is getting bad.

Those rear lines are not cheap and are a PITA to install. Mine busted out leaking good and proper and I had to by pass temporarily. IIRC that wasn't the easiest either.
 
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