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Radiator fan always runs when raining at idle

11K views 13 replies 5 participants last post by  Raptor 
#1 · (Edited)
I've noticed when ever it's raining the radiator fan will run when idling at a stop whether the engine is hot or cold. Soon as you start driving the fan will shut down. Nothing seems to change this behavior like fluid temp, A/C on or off, heat, wipers, lights... The fan is pretty quite so you won't hear it spool up or down if the radio is on or people talking. It happens every single time is raining.

I can only think I either have a short caused by the water but if that was the cause I'd think the fan would always run and not shut down once the car is moving. Or, this is some programmed logic I don't understand, perhaps to keep the engine/belt dry or the radiator clear of water droplets. Anyone else notice this?

Update: I've given this a lot of thought and nothing makes sense except for a short on the A/C pressure transducer as the fan should have the same behavior if the A/C was on. Or what ever sending unit controls the fan with the A/C compressor is on, guessing it's the transducer. Guess I'll have to pick a nice rainy day to bring it to the dealer so they can reproduce it, which is slim pickings here in California.
 
#4 ·
I recall a lot of people (with various vehicles) complaining about their radiator "smoking" at a stop in rainy or snowy weather.. I wonder if this is a "feature" to keep water that evaporates from the surface of the radiator from being visible?
 
#5 ·
I ran with that theory and figured there must be an exterior humidity sensor if this fan behavior is intentional. Unfortunately I did not see one in the mopar parts catalog so I'm back to the some a/c sensor must be shorting out when wet.

I think I'm going to get a spray bottle and see if I can activate the fan spraying sensor connections that might get hit by rain. I love a good mystery.
 
#6 ·
I finally got this fixed. Turned out to be a loose/partially connected wire for the PCM low speed signal wire at the fan module. I had to wait almost a year for another rainy day in California to bring it in so I know they could reproduce it. The tech also updated the PCM software which was 5 revisions old just in case, I have an early build on Sept. 2013.
 
#7 ·
Vertrkr, Well I have noticed the same on my Hemi. I can not hear it when car is running, but fan will be running on hi speed for a second or two when I shut the car off. Again only when raining. Never does it when dry. Had it at the dealer to have my front bumper fixed (starting popping out where it meets fender). I explained it to them, but of coarse the found nothing wrong and said it was normal. Not sure if Hemi fan is set up the same as the V-6 but I will certainly look into it. Was the connection that was loose near fan?
 
#8 · (Edited)
Vertrkr, Well I have noticed the same on my Hemi. I can not hear it when car is running, but fan will be running on hi speed for a second or two when I shut the car off. Again only when raining. Never does it when dry...
Turns out mine still does this. You need good hearing to hear it spool up when running. I only notice it when I stop at a light, I can hear it spool up a second later after I stop or when I turn off the engine you can hear it spool down. Like you, only if it's raining and doesn't matter if the engine is cold or hot.

Maybe it's a feature but has sure stumped the service dept. They searched Star cases and even said they pulled both fan relays and the fan still ran which they thought should kill it. If it is a feature I sure as heck don't understand the logic .
 
#9 ·
LOL me either. Only logical thing I could think of is that it had some type of sensor to keep it running if wet so that people did not see steam coming from front of car (water hitting hot radiator) when stopped. Dealer had no idea, said they checked for codes etc. but they blew it off. I'm like you, I like to know the reason behind everything. Maybe its normal. but would certainly like the reason why and what makes it do it.
 
#10 ·
Went back to the dealer at their request so they could record a data stream to send to Chrysler engineering. The manager hooked up a wireless transmitter to the ODB II port then we went back to his office and checked out my car on his computer. The system is pretty cool showing a live stream status of everything from relays to how fast the fan was spinning. My fan was running at a constant 15% power never cycling off. When driving and I come to a stop the fan will jump to 100% for a minute then reduce to 15% after a minute and stay there. He couldn't fathom an explanation so hopefully engineering will have a clue.
 
#11 · (Edited)
I finally have an answer to end this story. My service manager heard back from Chrysler engineering and they said it is working as designed. Engineering said when it's raining they expect you to use the A/C to clear window fog so the fan is always running in anticipation of the A/C being used. Sounds like a waste of energy to me as in my climate my window don't often fog when raining and why the fan can't just stay off until the A/C is in use is beyond me but there you have it for better or worse.
 
#13 ·
There is a humidity sensor so I guess that must be it. The fan is actually always running, just kicks in to high speed at stops or very low speed much like running the A/C in the summer.

I'm not 100% convinced but enough so not to worry about it anymore. I'm still a little surprised we are the only ones to comment on it, I posted this in all the durango forums and some other mechanical auto sites.

Anyway I'm on to the next problem to ponder. I keep having to refill my power steering from the min mark every 4,000 miles. Not visually leaking anywhere so I suspect it's slowly filling up the boots and will eventually show a leak.
 
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