Coolant in heat exchanger core

[workmaster2n]

I was doing the regular engine servicing today when I had to remove the heat exchanger end cap in order to fish out a broken raw water impeller vane. When I took the end cap off, I noticed a couple drops of water fall down (as is expected), but then I noticed there were a couple drops of water that had a yellow/greenish tint. It didn't look green enough to be corrosion, and we use green coolant.

If I took a micofiber cloth and pushed gently against the end of the heat exchanger stack, a couple more drops of this colored liquid came out onto the microfiber.

I haven't noticed a drop in my coolant levels (I don't have an expansion bottle, I just eyeball the level before I start the engines).

The heat exchangers were last serviced 2 years ago. The engines are Nanni 3.75 HE's.

If this was actually coolant, I feel like the 2 ways it could get into the stack would be through a crack in one of the core tubes or around the oring at the end cap.

I'm not sure where to really start with this one and if it's even a problem.

[Shrew]

Originally Posted by workmaster2n

I feel like the 2 ways it could get into the stack would be through a crack in one of the core tubes or around the o-ring at the end cap.

The O-ring on the end cap just seals the raw water in the tube. It doesn't separate the AF from the raw water. The coil pack is isolated from the raw water. IMHO the coil pack has failed.

[fourlyons]

Originally Posted by Shrew

The O-ring on the end cap just seals the raw water in the tube. It doesn't separate the AF from the raw water. The coil pack is isolated from the raw water. IMHO the coil pack has failed.

The o ring most certainly does separate the AF and raw water. I have this exact engine so I know this is true, but it's also true with many other heat exchangers I've met. Given that the AF side of the cooling system is under pressure when hot, the AF will want to leak to the raw water. But, as it cools it can produce a slight vacuum and pull raw to AF.

On this engine, the o ring sealing surface at the outlet end, is a known failure point due to corrosion of the aluminum heat exchanger housing. I installed an anode in the end cap to address this two years ago. Only time will tell, but so far it's good.