Background on this from another thread is that I was having degas pressure under high load on hot tunes. I suspected (as did others) a small head gasket leak. Mechanic didn't believe it was head gaskets. He checked everything he could and theorized that coolant was deadheading at the back of the heads and causing the pressure. Didn't seem plausible to me so I pressed the issue and he agreed to pull the heads but said he wanted to put a coolant return on it that circulates through the back of the heads back to the thermostat housing. I agreed and had him do a fuel regulated return at the same time, and then got caught up in Odawg Diesel having a 4th of July sale on their intake manifold so I added that to the list of replacements too.

Some on here thought the pressure could be from boost going past the closed egr valve and the welded egr cooler and that my egr cooler (which was deleted by welding on the intake side and a straight up pipe not hooked to the cooler on the back side) was cracked and leaking boost into the coolant system. This wasn't the case. EGR cooler was dry as a bone and there wasn't even a plug on the exhaust intake side so it would have been leaking coolant out the back if that was the case.

Anyway, long story short, there was no leak on the head gaskets, no ruptured egr cooler to cause the pressure. He used Evans waterless coolant and I'm running an Atlas 40 FICM tune with Innovate Xtreme X PCM tune, along with a Powermax turbo. It's all back together now with the coolant return and I cannot get the coolant system to pressurize above 3psi no matter how hard I push it. Before it was hitting 16-18psi and venting off at the cap when I ran it really hard. I'm leaning toward the conclusion that he was correct. I don't understand all the dynamics of it, and I still wonder if the different characteristics of the Evans coolant could have something to do with it, but the coolant return fixed the issue. Nobody else agreed before hand and I still don't understand it completely, I just know truck is running awesome now and there is not and issue any longer. BTW, it has noticeably more power now, whether it be from the regulated return keeping pressure up (had blue spring already previous to this) or from the ported intake manifold, it seems to just keep accelerating where it started to lay down before.

 

Glad to hear you got it resolved.

(Can I get a tenth a point for speculating the head might have a hot spot or micro boiling).

A long time ago on TDS as I mentioned before was a cooling engineer who worked on the 6.0 and went through the Evans debate. He had talked about other motors that had issues with heat transfer using Evans, and about 100 years ago I knew of a situation of the micro boiling on a production motor turned racer. Fluid cooling is weird science and gives me a headache, but you can get into weird situations where altering fluid direction alleviates the issue.

I actually think it's was a problem on the one Ford compact tractor I have. As I go through tractor salvage yards you see a good number of that model, all with a bad head or broken crank. Almost every time. When you pull up the service head gasket for the tractor two of the cooling pathways of the revised gasket are closed off. No TSB, no recall. Just an in-service maturing changed a head gasket, and in the parts book a reference to an updated gasket.

So the builder may have had a very good idea of what was happening. And fix for it. Hope it stays that way.

 

How about 10 points... :-) Thanks for your input. It seems to be a rarely discussed issue as it's mostly a non issue, but seems in my case it did prop up. Curious if it would have done the same with ELC coolant but we'll never know now. The Evans is supposed to be lifetime coolant but I imagine there is a prudent interval to change it out. I'll have to look more into that.

 

No, it was a SWAG. 0.1 point.