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I refurbished the head on the air compressor about six months ago. The mistake I made was cleaning the mating surfaces with an abrasive material. I have had a significant coolant leak most recently at about a gallon per 1000 miles. Obviously I've been concerned about the head gasket, but have baked the dpf, replaced the doser injector, and inspected the crankcase breather multiple times. There was no evidence of coolant during any of these procedures. There also has been no evidence on the dipstick of coolant mixing with oil. Also there has been no combustion or other residue in the surge tank. It is perfectly clean. So I settled on the probability that I damaged the compressor head during cleaning. Additionally, I began to notice moisture around the exhaust port of the compressor head. I had a cab air bag that was 6 months old, but I found multiple pin holes, creating a significant air leak. This caused the compressor to cycle every 2-3 minutes. After replacing the air bag, the compressor cycled much less often, and I noticed my coolant loss was reduced significantly. This, to me, was further evidence of a leaky compressor head.
So I'm home now and doing some maintenance. First on the list was diagnosing the compressor. After removing the steel braided line to the dryer, I did notice some coolant. Second, I removed the intake line, and this is where it got scary. The compressor intake line had a lot of oil in it. So I'm thinking turbo. I disassembled the elbow from the cac and saw a coating of oil in the boot. Freaking out now. I went around and removed the clamp at the turbo outlet. Whew, it's dry.
Back around to the compressor side. I installed the elbow to extend the intake for the compressor and minimize egr from entering the compressor intake several months ago. I realized the oil wasn't coming from the egr side, so I finally concluded that the compressor was forcing oil out its intake. I've seen bad compressors push oil into the discharge stream, but this has me stumped. Obviously I've been concerned with the large amount of coolant loss that it's been going to the air dryer. The purge valve is wet with oil and I guess coolant as well. I'm attaching a pic of the scoring on the compressor cylinder to see if anyone thinks this much oil is getting past the piston. I kind of don't think so, but where else would it be coming from? Is the line for the governor a possibility?

I’ve seen worse. This is what EGR soot does to everything.
If you can’t live with it pushing little to moderate amount off oil to your air dryer, you have to replace it . That’s the only option and right way . Make it right .
When unloader is open the piston pushes air back and forth on intake side and oil can go there. So don’t freak out.
Almost forgot. The blow by and crankcase pressure helps a lot for oil to get true the scoring on top off piston.
The good thing is , you found the source for coolant loss . So you can sleep better.

Just a reminder. Torquing sequence and torque is crucial when installing head .

I'll take a picture of the intake and post tomorrow. It's thick. So the oil is coming from the compressor? I can't think of any where else.
Good info on unloaded valve. I'm going to conclude that oil blowby is excessive. One thing I didnt mention is that iI already bought a new head. Guess I'll return it and get a new compressor. It has 690000 miles on it.
Thanks.

For sure is new compressor time then . Do it right!!!
Don’t forget to change the air dryer filter .

I'm actually thinking of replacing the whole dryer. The purge tank is badly corroded.

My ID-IS does not come with the wet tank. That is a separate purchase item.

I'm actually thinking of replacing the whole dryer. The purge tank is badly corroded.