Hi, my name is Ed. Thanks for writing!I think you've followed the problem almost completely to solution and the lack of electric fan operation is almost certainly the cause for your temp gauge fluctuation. The fact that the mechanical cooling fan clutch engages and saps power pretty much proves the point that engine heat is reaching the radiator.... or the fan clutch wouldn't lock up solidly as you've described.
The cause seems to be with the electric fan, but will likely be an output of the fan relay, rather than a control-side issue, which will set codes.
What might be the easiest approach to the problem would be to see if the cooling fan actually spins when power is applied. The ISO-20 relay your Durango uses makes jumpering the circuit pretty easy. Pull the relay from the power distribution center (PDC for short) and locate the two terminals that are parallel to one another and larger in size. These are the supply and output feeds, which if jumpered with wire... paper clip... needle nose pliers... will send power directly to the fan motor. If it fails to fire up, we need to look more closely at the feed or the fan motor it
With the ignition on, jumper in place the fan doesn't come on.
Cool. That's the first step. I figure that the feed to the output is in place to start. You'll be lacking a complete circuit somewhere, whether it's a feed to the motor, the motor itself or the ground.
See if you can disconnect the fan motor connector down at the fan itself. The wire that isn't black will be your power feed from the relay. Jumper power to the circuit like you just did and see if it appears at the 2-wire connector.
The fan motor connector is a little complicated. There is a red slide-lock that has to be clicked to its opposite position before the release tab will be enabled. Once clicked (not removed), the slide lock will allow the connector to be separated.
If checked electrically, testing for voltage at the feed wire when jumpered (connected or not) tells you that relay output is making it that far. Then testing the ground circuit (other wire) when connected at the fan will tell you whether the ground is good.
Lack of voltage at the ground circuit.... and no fan operation... means the motor is bad.
Seeing voltage at the ground wire means the ground is bad. No voltage should be present in amounts over one volt ever on the ground side of operations.
As long as you're in the area, you might just stick a finger inside the fan cage to see if the blades will spin. This is without power applied of course lol!
Physical obstructions will usually cause the supply fuse to blow, which also supplies power to the feed circuit of the relay and will cause a code to be set. Since you have no codes, I don't expect this to be the issue, but it's good to know if something crawled into the fan and stopped it or not. Just because.
Quick question... is there any sparking when you jumper the feed and output circuits? No spark means the circuit is open (broken) and sparking with no reaction from the fan means you have a complete circuit but there might be a short circuit or physical obstruction to the fan blades.
Your are getting way ahead of me. I checked Power at the cable going to the fan but am not getting any power. I have the relay jumped an ignition on.
I am getting power across the solenoid jumper.
Is there something between them?
Is the electric fan 12 volt? I could jump the wires to see if the fan works. have to make sure first/.
No power when jumpered? Check the feed you're using to be sure the circuit is live. One of the two parallel terminals (as opposed to the three parallel terminals) will be powered continuously by straight battery voltage if the feed is good. Let's see if the basic feed is present.
A test light or voltmeter will work for this. Do you have either one handy?
at the relay jumper i have powr
on both sides/
no power on either terminals of the fan
cable coming to the fan
what is between them?
Jumpering is what I described earlier. Locate the two large terminals that are parallel to one another and jump the circuit using something appropriate. A paper clip will work but will likely heat up a bit in your hand if successful, so be aware of that.
Everything (except ignition system output voltage) is 12v on your Durango.
Lemme check. Be right back.
I jumped the plugin for the relay. I'm getting 12 volts on both sided. the plug in for the electric fan is still showing 0 volts on both terminals
The wiring diagram shows output to the fan itself to be uninterrupted by intermediate connectors. It shows it to be direct-wired from the PDC relay itself to the fan motor, so the interruption will be near (or at) the PDC itself it appears. I was wrong in my assumption that the basic feed serviced both the control and output sides of the relay by the way...
Fuse 15 of the PDC shows to be the output source, which if present at one of the two big terminals of the PDC will be intact.
Output of the Fuse 15 circuit (50 amp fuse) follows the light green wire to the fan itself, with the black wire being the ground circuit. If you can't connect jumpering of the fan feed to the fan motor itself on the light green wire, the problem may well be within the PDC itself. Examine the terminal connection area in the PDC for signs of overheating or melting.
my diagram doesn't say fuse #. its the cover to the fuse block.
Yeah, funny how that works.
You'll need to just find the 50 amp fuse that services the fan motor circuit, which should be identified verbally on the under-cover road map.
all the 50 amp fuses work pw seats, start
But if power is supplied at either of the two large terminals under the relay, it's all good. Otherwise, look for a bad fuse, which might not be evident visually since these large fuses can blow without being obvious about it. A 50-amp fuse is a red one I think... but don't hold me to it!
pw windows, & ign
No matter. Do you have power at one of the two large terminals under the fan relay?
It appears you've gone offline. I'll continue this with you tomorrow if you have any questions.
I droped a fuse and can't find it.
found it. I am still not getting power to the wires going to the fan. I have power across the relay as you said but still not power at any of the wires going to the fan motor
That doesn't look good for the PDC itself. The path from your Fuse 15 feed (one terminal) to the fan motor output (the other one) is pretty short. My information has become a bit contradictory by the way....One diagram shows the output circuit to be light green, where another one shows it to be yellow. It might be the difference in engine controllers, but the net effect is the same... no continuity between the output terminal and the fan motor means something between those two points is affected.
My information (and memory) show no intermediate connectors involved at the PDC, which means the PDC is part of the engine wiring harness and isn't serviced separately. We can work out an alternate path for this circuit to work if you're willing to break out the soldering gun and a few feet of wire if it comes to that. It's a lot cheaper than a whole new harness...