Crystals at heat exchanger end cap

[workmaster2n]

The last time I took the boat out, I noticed that the coolant in one of the engines was a bit low. Looking in the bilge, which is usually dry, I noticed a small amount of green liquid. I figured the planets had aligned and somehow the engine heated up a bit more than normal, and some coolant had boiled off (I don't have a coolant reservoir, just a drain hose from the pressure cap).

I topped up the reservoir with a couple dashes of coolant (call it 100 milliliters), and went out sailing for the day. The next day, the coolant was again back to its lower level.

I took a closer look and on the end cap of the heat exchanger, I noticed a ring of crystals. I can't tell if they are salt water or coolant (maybe I should have my noisy neighbor do a taste test...). My guess is the oring at the end of the heat exchanger tube assembly has perished and needs to be replaced.

I've read up on the manual and this seems like a fairly straight forward process, but are there any other things I should keep an eye out for? Given that I'm low on coolant and there is coolant in the bilge, I'm inclined to think the coolant has been exiting the system and not that salt water has been entering the coolant reservoir.

It's a Vetus M4.45 if that makes any difference. Salt water cooled.

[tkeithlu]

The coolant is going into the bilge rather than out the raw water discharge or exhaust, so a link between raw water and coolant does not sound likely. You've found a leak, so pull it apart and see if indeed that O-ring is damaged. Good hypothesis.

As a matter of avoiding confusion "salt water cooled" is usually reserved for engines that use raw water itself in the coolant passages, a practice that soon results in the engine becoming semi-attached bits of iron. It is common in freshwater only engines. Your engine is cooled with a heat exchanger.

[SkipperRichard]

I am about to service my heat exchanger which politely announced its needs by taking out my starter solenoid. Have removed the unit and it has some salt deposits and scaling and minor pitting around gasket surface. I can see this is solid copper and have located a person who can braze and resurface. My motor is a Volvo Penta 2002b.

Has anyone done this project on this motor? Anything I should be looking out for?

[Compass790]

As a matter of avoiding confusion "salt water cooled" is usually reserved for engines that use raw water itself in the coolant passages, a practice that soon results in the engine becoming semi-attached bits of iron. It is common in freshwater only engines. Your engine is cooled with a heat exchanger.[/QUOTE]

I'd dispute that salt water cooled engines necessarily disintegrate. There are plenty of sub 1980 raw water cooled engines run in the sea locally still in good shape corrosion wise as long as the owners keep up with the anode maintenance

Not looking for an argument, just IME.

[Mickeyrouse]

I used to have a boat with a raw water-cooled Atomic 4. It sailed in the Gulf of Mexico for 30 years. At the end it became a pile of rust that resembled an Atomic 4.

[Squanderbucks]

End caps are typically sealed with large flat rubber gaskets with a central hole. The crystals you are referring to are salt crystals that slowly build up over time. That is normal. Periodically the gasket is supposed to be removed and the end of the exchanger cleaned and the gasket cleaned and expected and replaced. The little rubber or copper o-ring under the bolt requires replacement a little more often. Some people use a little white Teflon based sealer from Prmatex around those.
The big gaskets are not totally waterproof and with the heating and cooling of the engine thin films if water get under the gasket. When it dries the crystals form. If not cleaned from time to time the salt will build up and expand enough to push a gap big enough to leak or weep.
I always have one rubber gasket and o-ring in my parts box. Maybe replace it every 4 or 5 years.

[tkeithlu]

Hey, Squanderbucks - That was a really informative response. I learned something today.

[Jolly Roger]

I am just re-assembling all the water system parts on my 40-year-old Perkins 4.236, after removing and cleaning all the pipes, including the heat exchanger, exhaust, and both raw water and fresh water pumps. It has probably never been done in the life of the engine, and clogged up is an understatement!
The heat exchanger has 100 1/8” tubes inside, of which I think only 20 or so actually passed water. It only has one end openable with a round rubber gasket, the other end is sealed. (Read squanderbucks post), I dissolved much of the blockage using Rydlyme Marine dissolving fluid, then, (very carefully), rodded the tubes with a long 1/8” drill. Perkins are not renowned for being easy to work with on a boat, whereas my three-cylinder Kawasaki generator diesel has caps both ends of the heat exchanger, and it’s easy to clean and they don’t leak.
The heat exchanger on freshwater cooled engines is a very important, delicate, and vulnerable piece of equipment, very often overlooked—until an overheating occurs.
I am hopeful that this time-consuming and expensive exercise will cure a long-held overheating problem.

[Q Xopa]

It's not commonly done but a periodic fresh water, or even mild muriatic solution treatment of the heat exchanger can be done by some mechanics with varying degrees of success, depending on how bad it has been allowed to get.

Or if your really dedicated to the care of your boat engine.

Permenantly plumb into your Raw water system a freshwater flush system. Three Tees and a couple of valves plumbed to regularly fresh water rinse all of the saltwater systems- galley faucet, anchor wash down, main motor, dinghy outboard, even thru hulls etc. Its reasonably cheap and simple considering the expensive corrosion issues you could eliminate, or at least reduce.

Obviously best if you have ample fresh water, like a Watermaker installed.

Just a thought.