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Old 10-20-2021, 02:04 PM   #1
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DEF lines

is there a way to tell if the def lines are installed wrong like ive seen In other posts. The original owner said he had to change the def head but did nothing with the lines. Do the lines have anything to do with the def head failures? Thanks
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Old 10-20-2021, 10:08 PM   #2
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Basically the coolant supply line running from the top of the motor (pink line in drawing) should run to the front bulkhead thru frame fitting. What happens with the reversed lines is it can overheat the def to a point that it starts destroying the sensors on the def header unit. The def header has 3 sensors on it, one for level, one for quality and one for temperature.
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Old 10-20-2021, 10:32 PM   #3
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Thanks, ill see if I can trace it
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Old 10-20-2021, 10:43 PM   #4
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Quote:
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Thanks, ill see if I can trace it
It can be tricky to trace and keep track. I used an orange paint pen and marked the line every 6” to keep track of it.
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Old 10-21-2021, 06:16 AM   #5
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Just because a DEF Head was replaced doesn’t mean the coolant lines were, or are, crossed. There is a whole batch of bad DEF Heads out there that are hitting a bunch of folks. My saga with 3 DEF breakdowns returning from our Wyoming trip is well documented. The lines on my rig were not crossed and were checked at multiple FL dealers as early as 9 months before the breakdowns began.
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Old 10-22-2021, 10:29 AM   #6
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What about sensing the temperature of the two lines at the connection INTO the DEF header after starting a cold motor and warming up? I would assume that the one line that gets warm first should be the inlet to the header.

Easier than tracing them along the frame rail?
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Old 10-22-2021, 06:02 PM   #7
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There can be more than one cause for a DEF head failure. As posted a year ago I went through about 3 DEF heater control values which would fail because of reversed heater line in my DEF tank. Then the DEF header failed. Since then June of 2020 I have had no failures or problems with our 2018.5 Seneca. We have put on about 12000 miles. When the hoses to/thru the DEF tank were reversed the DEF temp would go up to around 160 degrees. That was the measurement made when they found my lines reversed. With the lines correctly installed they should not allow hot coolant to run thru the lines when the ambient temp is above 32 degrees. I now run a BlueFire and watch the temp closely. Haven’t yet but do intend to install a shut off valve on supply side of the DEF heater hoses. On warm days you can see the temp go up on the DEF tank and it directly impacts the quality of the DEF as it goes up the DEF % goes down. I never run more than a ½ tank of DEF just in case it gets to low I will drain it and put in fresh. I believe that some of the failures of DEF headers could be from low quality DEF sitting in the tank, and summer operation with the DEF warming up. Just makes sense to me.
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Old 10-22-2021, 09:00 PM   #8
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Thanks, plan getting bluefire also. That tell me for sure if there reversed
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Old 10-26-2021, 02:11 PM   #9
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I cant tell for sure by looking at the diagram , dose the upper hose on the manifold go directly to the def tank or dose that one go to the solenoid just before the tank? Thanks
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Old 10-26-2021, 05:58 PM   #10
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I cant tell for sure by looking at the diagram , dose the upper hose on the manifold go directly to the def tank or dose that one go to the solenoid just before the tank? Thanks
The hose from the top of the motor goes to the forward through frame fitting and then to the control valve.
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Old 10-26-2021, 06:51 PM   #11
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Thanks I'll check again tomorrow
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Old 10-27-2021, 03:52 PM   #12
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Well it appears the upper hose from the top of the motor dose not go to the regulator. Looks like ill need to flip the lines. Hopefully its not to late.
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Old 11-02-2021, 07:52 PM   #13
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The hose from the top of the motor goes to the forward through frame fitting and then to the control valve.
Brian,
where did you get that color illustration? It references other pages, so did this come from a Freightliner manual? Great work posting this for our use. Very helpful, as always.

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Old 11-02-2021, 08:08 PM   #14
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Came across them here.

https://postimg.cc/gallery/Fzp3Rcg
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