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Discussion Starter #1
So heres the story.
2004 F350 CCLB 6.0
Towing my 7k lb trailer on vaca thru indiana..basically flat.
First 2 hours temps all good....EOT 215 ECT 208.
Last hour things go wierd.
ECT drops to 199 and then proceeds to bounce around from 171 to 208...it will not stay pinned. I know it is not 171 though!
and the EOT starts to climb and runs in the 220's and as high as 233.

All numbers are measured using the Torque App.
Truck runs fine thru it all and dash guages never fluctuate.

Also the truck has a tendency at times for the ECT to "lock in" on a temp or 3 and simply move between those numbers. Yesterday it was 204.8, 206.6, and 208.4. Normally if i shut down the truck and restart it she works properly. I just couldn't do that yesterday as we had 2 other tucks with us and i didn't want to stop the others or turn off and on the truck rolling down the highway so i lived with the wierd ECT numbers.
But the climbing EOT temps for no apparent reason....when the numbers had been perfect for 2 hours!

the truck was redone with now head gaskets, studs, oil cooler and much more in 2018 and has 5k miles on it since then.

What are your thoughts on what is going on here?
 

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Fan clutch working normally?


Sent from my iPhone using Tapatalk
 

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Recommend looking at the EOT and ECT sensor For pinched wired oil or any sort of damage. My guess is your ECT sensor pigtail or wiring could be failing.

If you can monitor ECT voltage and ECT and look to make sure the voltage doesn’t freeze as ECT changes. ECT can lie, but voltage can’t. THe sensor uses voltage to measure, if the ECM doesn’t get a correct voltage for what it thinks it should be, the ECM gives an ECT. Inferred mode.
 

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What @ChrisSki said ^^^^

The PCM uses these sensors to operate the fan clutch, fuel rate, etc
 

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The only time I have seen bouncing ECT temps that wasn't electrical was when a large radiator leak caused a very low level in the coolant and the temperature sensor was periodically in an air pocket and, (because of its heat transfer being less) would drop in temperature. How's the level in the degas bottle?
 

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Discussion Starter #6
Degas level is good. When we got to
home i did notice the fans were on with AC not in the ON position...was on VENT setting
 

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Diesel DB
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Watching this thread. I've had the same issue as you described but with both the oil and the coolant but never at the same time. It's not a big deal when the oil temp drops but when the coolant drops (sometimes by 20 degrees) the fan doesn't kick on. I live up a mountain so I'm always watching the coolant temp on Torque Pro. I either need to figure out what's wrong and fix it or get the upfitter hooked up to trigger the fan. One thing I've noticed that seems to work about 75% of the time is (if I see the coolant going way down) punching the peddle at the bottom of the hill. It seems the temp will sometimes jump when I do that. If it doesn't then I just created a lot of extra heat which requires me to take it slow up the mountain. Like you've described, stopping and restarting can reset it but it's iffy for me. I've replaced both sensors for this reason about 2 years ago but it didn't fix it. I guess the next step is looking over the pigtails. I'll let you know if I find anything. Good luck!!!
 

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Discussion Starter #8
USAF93, Glad to hear i am not alone with this issue, sorry to hear youhave it as well I rebuilt the coolant pigtail on saturday. I noticed the wires were rather "bent" so figured why not. The oil temp sensor though, thats in a far harder and tighter location to work on but the wires seem bent there as well from years of heat and vibration right above the plug at the sensor. I ohm checked my connection i made and its good. Started the truck and saw the temp rising but havent driven it yet. Also i figured i would do one plug at a time and look for results. Both sensors are new, well 2 years and 6k miles, but new enough i believe. The problem never arose like this, to and from vacation, until i had about 2 hours of drive time in.I will update results
 
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Diesel DB
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Where did you get your pigtails? Hope that does the trick for you!
 

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Discussion Starter #10 (Edited)
Where did you get your pigtails? Hope that does the trick for you!
My NAPA was able to get them for me. It took them a lil research but they found'em.

Amazon also has them for cheap too.

 
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Discussion Starter #12
for a quick test, swap them around and see if the readings follow the pig tail or the sensor.
swap the sensors? are they the same part? if so, thats a great idea.
i guess ya would lose a touch of coolant as its low in the system but if you removed th ooil sensor first and had it ready to go in the coolant hole the coolant loss would be minimal
 

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Vent the pressure off the coolant first ;)
but, yeah go quick not much coolant loss at all
 

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Discussion Starter #15
I dont have them infront of me, but I thought the pig tails were the same two wire plug
I believe the pigtails are the same. .just was not sure of the sensors being the same. I assumed you meant swap sensors
 

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The sensors are the same, so are the pigtails.
 
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