Can anyone tell me what this hose is and were it goes?

It's a coolant hose for sure but what its cooling I don't know. It starts on the rear of the egr cooler close to the fire wall and then goes down to the back of the trans were it loops around and heads back to the front somewhere. Also does anyone have an idea on how to fix it other then replacing the entire hose because that is turning out to be a huge pia. 2016 cascadia dd15 10 speed. I downloaded 3 pic and it did what it did but you get the idea.

 

By your description I would think it goes to a transmission cooler, but I have no experience with your truck or engine.

 

Are you sure those aren’t your def tank heater hoses …

 

Looks like that to me too

 

You probably need to replace the whole line. That hose is made by heating the nylon hose and sticking a plastic barb inside of it. If you cut it and put a new barb, it will most likely be too short or make the bends in the hose not line up with the mounting points any more. As a temporary fix, you might be able to splice a rubber hose to connect the broken line to the fitting again. If the barb is broken off inside the hose, then it will allow you to tighten the hose clamps without crushing the nylon line. I've done 3 of the 4 DEF heater line connections like this a few years ago on my Volvo as temporary fixes, and they haven't failed yet.

Another thing I would consider is replacing the threaded connections at both ends with fittings that you can put rubber or silicone heater hose over. But I wouldn't be surprised if the other end of that hose is like a sharkbite connection or something on a plastic nipple that requires O-rings to seal. If that's the case, I would still rather slip a hose over it and then put double hose clamps on it.

 

Well I figured out what it is. Took some pic's to freightliner and found out it was a supply line to the def tank. I guess maybe the pump in the def tank uses the coolant to keep it cool.

I spent hours trying to take the old line off and finally gave up and put the new line in around the old one. Took about 15 minutes. It worked and I was able to get the truck home were I will continue trying to get the old hose off.

All the clamps holding the old hose on are on top of the trans area which means I have to get a socket wrench and vice grips up over it from underneath blind. My hand muscle were continually burning. It was a pain is an understatement.

I was thinking about what you mentioned that is doing some sort of splice connection. I will keep your suggestions in mind for possible future situations.

 

Turns out it was a def coolant supply hose.

 

It was a def tank coolant supply hose.

 

It’s for heating purposes def freezes in winter ..

 

Oh, ok I didn't realize that. Interesting stuff.