Man I’m tired of these rotten DEF systems

[J&JD]

Yep, that should work.

You might want to leave it open and let the DEF header operate normally, and then upon failure you could use the valve. That way you would have an emergency "get out of jail card" to use until you can find a 4th replacement header.

But either way, I'd say your ahead of the game!

It’s not the DEF head that is acting abnormally it’s the valve that controls the engine coolant circulating through the head. When it fails it fails open which can then cause the head sensors to fail and then all hell breaks loose with engine warnings etc. if I don’t need heat circulating through the head why even chance it. I’ll leave the valve closed for now.

 

[redbaron]

It’s not the DEF head that is acting abnormally it’s the valve that controls the engine coolant circulating through the head. When it fails it fails open which can then cause the head sensors to fail and then all hell breaks loose with engine warnings etc. if I don’t need heat circulating through the head why even chance it. I’ll leave the valve closed for now.

I’ve kept mine closed since installing.

 

[Jim]

I’ve kept mine closed since installing.

Then why bother replacing the DEF header? Just put in the valve and call it good. Same end result.

 

[J&JD]

Then why bother replacing the DEF header? Just put in the valve and call it good. Same end result.

No, because the head was damaged and just putting in a valve would not cure all the codes the damaged head was throwing. The new shut off valve will , hopefully, stop a bad coolant circulating unit from damaging the new DEF head.

 

[Jim]

No, because the head was damaged and just putting in a valve would not cure all the codes the damaged head was throwing. The new shut off valve will , hopefully, stop a bad coolant circulating unit from damaging the new DEF head.

I think the damaged head only throws codes when the DEF overheats. A few cycles of not overheating and the code will reset.

If that is the case, and it certainly was the case with mine, then bypassing the DEF header altogether, which happens when you terminate the flow of coolant into the DEF header, will allow the required cycles to occur and the code to go away.

Or am I missing something?

 

[redbaron]

Temp is only 1 value.

Quality and quantity are the others:

When it overheats, it boils the water and changes the quality as there is less water and more pig urine.

This throws legitimate error codes with a working sensor. The sensor can still be good when the Valve is causing problems due to being open at the wrong time.

Eventually the heat will destroy the sensor.

So bypassing the ability for heat to enter will hopefully preserve the sensor.

 

[Jim]

Temp is only 1 value.

Quality and quantity are the others:

When it overheats, it boils the water and changes the quality as there is less water and more pig urine.

This throws legitimate error codes with a working sensor. The sensor can still be good when the Valve is causing problems due to being open at the wrong time.

Eventually the heat will destroy the sensor.

So bypassing the ability for heat to enter will hopefully preserve the sensor.

I get it. That's the reasoning behind not opening the "optional" bypass valve.

But my questions was, why even bother replacing the DEF header if nothing is wrong with it except for the faulty factory valve? Bypassing the faulty valve, and eliminating the chance of the DEF from overheating, eliminates the problem. So no reason to replace the DEF header.

And after 3 cycles, the codes remove themselves.

 

[redbaron]

Jim; I agree. I wouldn’t swap out a functional def head for a failed valve.

 

[Jim]

Jim; I agree. I wouldn’t swap out a functional def head for a failed valve.

After running my rig for the last year with a bypassed DEF header, I’m only going to replace it for resale reasons. Otherwise, I see no reason.

 

[Rd1]

I can certainly appreciate the desire to have a valve to shutoff the coolant flow in case of a valve failure. My 'undrestanding' is, the engine startup up procedure opens the valve momentary, and if the temp is not an issue, then it is closed till the temp calls for the coolant flow thru the DEF head. This also flushes the coolant in the def head.

The question is, with the valve shut permenantly, what happens with the coolant already in the DEF system? Would there be an issue with that coolant remaining in the def for months/years? Should the valve be opened from time to time to flush the coolant in the head?

 

[Rich W.]

I think the damaged head only throws codes when the DEF overheats. A few cycles of not overheating and the code will reset.

If that is the case, and it certainly was the case with mine, then bypassing the DEF header altogether, which happens when you terminate the flow of coolant into the DEF header, will allow the required cycles to occur and the code to go away.

Or am I missing something?

Well you’re both right but kind of mixing up terminology hence the confusion. And it is possible that over heated DEF (at 200+°) could certainly damage the sensors in the DEF header, so it’s a toss up whether or not it will require replacement. The test would be the aforementioned five or six ignition cycles to find out. But either bypassing the DEF header or installing a valve (and keeping it closed) will accomplish the same thing and unless you are traveling in sub 12° temps it doesn’t matter at all.

Stupid that they designed the valve to fail open because while it may seem logical to the climate calamity crowd that frozen DEF won’t work, a system failure due to damage from being overheated is much more significant and a lot of these valves have failed. And of course as previously mentioned, the DEF quality is also reduced by excessive heat, so having the valve fail open accomplishes nothing. And let’s not forget all the chassis that had the hoses reversed from the factory. And while truckers do drive in those low temps, we don’t but we are all lumped together whether it makes sense or not.

 

[JRS]

Please see the following pictures of my 2020 DS Freightliner DEF Head Hoses. Which hose should I shut off to prevent overheating of my fluid? After running for awhile will there be a temperature difference between the hoses? And.... is my thinking that the hotter hose will be the correct one to add a valve?
I know it's dirty and will clean prior to any work in the area.

 

[Jim]

Hi Joe.

Can't really tell which hose goes in and which goes out. But, I'm not sure if would really make any difference. If you stop the coolant from going into the DEF header, then you chose the correct line. If you chose the wrong line, I can't imagine that there would be a problem either as the heated coolant can't really circulate if the exit is closed. Right?

But on another note, if you join the two lines together, then nothing goes in and there is no chance of overheating the DEF. This is what I did, and I've had no issues since.

 

[J&JD]

There are no markings on the top of the DEF head to delineate which is in or out so it seems as if the lines can be switched to either of the head posts. It looks like it’s just a loop for the coolant to circulate. Jim’s remarks make sense to me.

 

[JRS]

Hi Joe.
But on another note, if you join the two lines together, then nothing goes in and there is no chance of overheating the DEF. This is what I did, and I've had no issues since.

I appreciate the comments from Jim and Jerry!
Based on what you and Jerry said, I'll be joining both lines together. What did you use to plug the elbows going into the tank? Any other tips appreciated.