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Chrysler Repair/radiator fan sometimes stays on in wet weather


QUESTION: I have a 2001 Dodge grand caravan with 3.3 litre engine.  I've noticed the cooling fan sometimes stays and won't shut off while the van is running in wet weather.  Please not this happens even though AC and defrost are off.

Not sure if this would be the relay or temp sensor.  Is there a way to test this?

In dry weather, all seems fine.  The fan does not keep running once the ignition is turned off.

I also noticed the radiator fluid is kind of rusty looking and not clear.  Would a flush perhaps be a good idea and could I do this myself.  I've heard of Prestone kits which splice into the hose and supposedly do a complete flush.  Would you recommend this and if so any advice on how you would do it at home. I've heard that most lube shops and regular shops cannot be trusted to do a good radiator fluid flush.

ANSWER: Hi Gary,
The fan usage is complexly dependent upon the engine coolant temp sensor, the ambient air temp sensor, the transmission coolant temp sensor, the vehicle speed, and the a/c pressure transducer which all provide inputs to the PCM which then controls the fan speeds proportional to the need. I would not worry about a connection to wet weather except for the possibility of a water intrusion into the fan relay which is located in front of the radiation on the structural member that runs across the body at the lower edge of the radiation. So long as the engine coolant temp is staying in the 1/4-3/4 of scale area it is not a problem.
Yes, you can do the radiator drain, flush, refill yourself using a kit as you describe. There are several pages from the '04 manual I could copy and attach to an email that give the basic info. Tell me your email address (but don't use @, instead use "at" or it will be erased automatically) if you want those.
Please read the PS (below) and respond to it.

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QUESTION: Ok, I will keep an eye on the fan.  My concern is that the fan will wear out if it stays on for days on end during wet weather. I am guessing it will likely be difficult to diagnose this if it only happens during wet weather. When it's doing this during wet weather, if I shut the vehicle off, and restart it after a couple hours, the fan immediately kicks in and stays on even when the coolant temperature is cold. Funny that it only happens during wet weather with high humidity.  If you think of anything else to consider, please let me know.

Yes please email me the flush info at garnita"at"  Can you tell me what type of coolant to use and how much I will need.


Hi Gary,
Except for if you have the defrost or A.C. activated the fans should not come on immediately after starting the engine. However, why in wet weather is an unknown to me.
I will send the pages shortly. The capacity of the cooling system is 13 quarts if you don't have the rear heater, or 16 quarts if you do have than heater. You mix ethylene glycol with distilled water in equal amounts. It is recommended to use the fluid with hybrid organic corrosion inhibiter if available.
Thanks for the rating and nomination. You can do it again if you so-choose for this answer.

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Roland Finston


Free fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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I have do-it-yourself experience (50+ years) and a library of 100 1982-2011 Chrysler factory shop manuals and 20 multi-manual Chrysler Corp. CD's.

I was voted "Top Expert" 2010-2015, here at AllExperts, and have answered 20,000+ questions.


Five decades as a 'do-it-yourselfer' on domestic and imported cars.

Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

Advanced degrees in Physics/bruised knuckles

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