The Cummins 6CTA engines in my Roamer are aftercooled turbo diesels. The aftercooler housing is cast aluminum, but the core is made of bronze. Since raw water runs through the core, these aftercoolers are notorious for the sort of corrosion problems you’d expect from dissimilar metals in saltwater. Making matters worse, Cummins apparently assembles the aftercoolers dry, with no grease, Tefgel, or anything else to lubricate the joint, isolate the metals, and make disassembly easy. These engines only have 400 hours on them, but they came from New York and ran in saltwater. There’s just a bit of the green verdigris around the lower aftercooler end cap, which is telling me it’s time for service. The diesel gurus at boatdiesel say the aftercoolers should be serviced every two years, and I’ll be following Tony Athens’ method.
After I popped the top off the aftercooler, I found a bit of aluminum and copper oxide outside the o-ring seal. This tells me there was a slight leak at the o-ring. I’m glad I decided to tear into this.
The hex bolts holding the ends on the aftercooler are standard sized. Unfortunately, that brings the edges of the hex heads so close to the bronze castings that a socket won’t fit. This isn’t a good scenario for an aftercooler that was leaking saltwater.
I need to order new galvanized shoulder bolts for when I reassemble this. And they’ll get slathered with Tefgel when this goes back together.
The core tubes are clear now, so water flow won’t be restricted anymore.
The water side of the aftercooler cleaned up pretty well, but the air side is still a question. Because the bronze cores were installed dry into the aluminum housings, I couldn’t convince them to come out. So I brought both aftercoolers down to the house, stood them up on end, and poured some automatic transmission fluid into the air side. Two days later, ATF started dripping out of one and a week later it started dripping out of the other. I flipped the housings over and repeated the process. Finally, after two weeks, some heat from a MAPP torch, and occasional encouragement from a 3# sledge hammer tapping on a block of wood laying across the top of the core, first one then the other core came out.
Fortunately, the fins all look good and the corrosion on the ends was minor.
I’m soaking both cores in degreaser now and will clean them up over the weekend, then I’ll reassemble next week. In the meantime, the window shop finally sent replacement trim rings for my helm station windshield. Adding to the potential drama, a blizzard is forecast for the area tomorrow and Saturday, with 50mph gusts and no less than 12″ of snow predicted. We’ll see how Tent Model XXX holds up.
Next up in our 1969 Chris Craft Roamer 46 Refit: Mid-Atlantic Blizzard 2016