2012 Peterbilt 386 Cummins isx 15 485 coolant problems

So I drive for my grandfather who owns a grain elevator here in MN. Always running hopper bottom at 80k. We average anywhere between 40k and 52k miles per year depending on harvest. Bought the truck in 2015 had 246k miles on it out of ohio. It was in great shape from what I can tell though I'm not exactly a mechanic. Changing fluids and filters are about the extent of my expertise. We had the def and egr deleted in 2016 i believe. Gained alot of mpg and power it seemed like, almost 2mpg on avg. ( i have a log I keep of every gallon of fuel i've put in and the date as well as at what miles and engine hours and what the computer said the mpg was. Also I write down every nut i tighten or even wiper i replace. Any work done by mechanics i keep a copy of in my logs.) Nothing else was changed in the computer.

Fast forward to last November on the first cold snap of the year. It was about 10 degrees and i was cruising down I 35W at around 7am when I look back in my mirrors and all of a sudden white smoke for like 300ft behind me so I turn off the engine brake and use the service brakes to stop on the shoulder. I see that it's coming from under the hood so i shut off the engine before i was stopped and grabbed the fire extinguisher, my phone, and my jacket. Im unlatching my hood while trying not to get run over when i hear water running. Sure enough the bottom big coolant pipe is laying on the ground spilling all my coolant. Which meant it's steam not smoke so I finally could catch my breath haha.

Now I know for a fact my coolant gauge had not gone over 210 in the time between the steam and my stopping so I figured I caught it in time and there shouldn't be any major damage I hoped. Called a local wrecker company explained everything and they sent a mobile service truck. Turns out this rubber sleeve holding the pipe on had a small hole in it, like the size of a pea. So he gets a new sleeve and puts it on fills me up we run it up to running temp at 180. It seemed like everything was fixed so after 4 hours of freezing my butt off with cars speeding by I was able to go finish my runs for the day, made 3 trips about 140 miles per trip.

The next day everything was fine until I got down to the elevator I was dropping at. I got out to use the porta potty and come out to a stream of coolant so i run to the truck and shut it off. Again I checked the gauge and it was around 200. Turns out he used the old hose clamps to secure the sleeve on and guess what it broke! So again they come out and replace both clamps which in hind sight i should have suggested but again I'm not a mechanic. Another 4.5 hours in the cold, luckily i dress for standing outside so i had coveralls and 2 jackets and gloves.

Couple weeks later after running like a dream, occasionally needing to add like a Qt of coolant in the mornings. I'm dumping a load and I hear a pop! I look to my truck and the dang thing is smoking again. So I check my gauge and shut it down. It was around 170 or so. It was just spitting out the overflow so I let it cooldown got out of the way and called my mechanic. He had me check some things, like loosening the cap and it was bubbling a little so he recommended I get it towed there so I did. Another 4 hours in the freezing cold. Another 2 getting hooked up and driving to the shop. He ends up testing stuff and replacing basically all the hoses gaskets and reservoir on the passenger side of the engine. Even replaced the big pipe that had fallen off. And changed the filter.

Since then the reservoir appears low in the mornings but when i open it i hear air and it raises the level, i usually add some just in case but then occasionally when idling it will spit out the overflow again. It's not happening every day but often enough to make me nervous. I've also noticed some issues with my air compressor not moving the needle sometimes for a few minutes. Then it builds up like normal and have no issue. At this point we're at about 425k miles. My brother in law is now driving it and he seems to be going through alot more coolant than I did and he seems to think it's happening more frequently. Sometimes I'll look in the yard and its steaming again, coming out the overflow. It's not much and does not make a big puddle. There hasn't been any oil in the coolant or the other way around it's still bright red.

Sorry for the long post but I figured backstory and more information would be helpful. Does anyone know what the issue is? I've read it can be the air compressor or head gasket / cracked head. Obviously I hope it's the compressor but I'd like to know more opinions. I trust our mechanic but everyone can miss stuff from time to time. Are there things I can do to rule out one or the other? Thanks for your time!