Cooling System Losing Water

[S.V. Taco Truck]

My 1996 Volvo Penta MD22L is losing all of the freshwater in the cooling system.

While running at 2,400rpm we Heard a loud pop and then the engine began to overheat. When we looked in the radiator there was no water in the freshwater side, which was full when we started. There was no water at the bottom of the hull and no water in the oil. When we filled it back up and ran the engine it drained in 5-10min.

Any idea what the issue may be? All ideas are appreciated!

[Rumrace]

Sounds like the heat exchanger is broken internally and your exhausting the water. Make sure it does not back drain into the engine. That’s my best guess

[tkeithlu]

Rumrace is 99 & 44/100% right.

Quick test: Dump a bottle of food coloring into a bucket of water and then use it to fill the cooling system. Start the engine, and watch the raw water where it leaves the boat.

[Shrew]

You could also check the oil to see if you 'grew' any more while it sat in the oil pan.

Check the bilge.

If the coolant isn't in the heat exchanger, isn't in the oil and isn't in the bilge, then the most likely probability left is that the coils in the heat exchanger are passing from the higher pressure closed cooling side, to the low pressure raw water cooling side and evacuating with the exhaust.

[sailormed]

Check if the leak is not in the coil in the water heater. Mine had a pinhole and wall water ended up in the engine coolant system.

[Rumrace]

Use red food colouring and scream out “ shark”

[Gary Matthesen]

Ha!
Had a similar problem of losing fresh water, couldnt figure out where it was going. Did all the similar investigation you outlined, no luck. Mine was a slower loss than yours.
Made my way into the aft cabin yesterday to tighten some lag bolts on the rear
motor mounts, when a slow drip from the HE hit me on the hand. It was green, culprit found!
Interesting is you would expect to find such a leak as colored by the antifreeze, must be so diluted by the time it hits the bilge I couldnt see it.

[Lancerbye]

Also check the hot water after applying a dye, if you have engine heated hot water. I have seen this happen when the coils in the hot water tank corroded.

[sailon46]

In my similar situation I was in Curaçao and ended up with a freeze plug having a big draining hole. Because was under the Turbo in. Yanmar 100 permatexed it and 5000 miles later still there no leaks

[Siberian Sea]

Most likely as the freshwater side of the pump produces higher pressure then the saltwater pump as the engine was running the freshwater side was forced into the saltwater side and out the exhaust as a result of a failure in the heat exchanger.

[boatpoker]

Originally Posted by S.V. Taco Truck

When we looked in the radiator there was no water in the freshwater side, which was full when we started.

Any idea what the issue may be? All ideas are appreciated!

Are you running water in your closed cooling system rather than coolant ?

[S.V. Taco Truck]

I will try the food coloring idea when I get back to the Marina. If that doesn’t yield anything, I will pull the tube bundle (what apparently the Brits l LLP call a tube stack). If that doesn’t yield anything, I’ll move on to pulling the whole heat exchanger. Just frustrating, as I just replaced the water pump on the same engine and was planning on rebuilding the whole thing in a year anyway. Thanks for all the suggestions!

[S.V. Taco Truck]

Problem solved. Somehow a path from the freshwater side to the exhaust port flange formed. I assume age and casting imperfection. This allowed the coolant to drain into the exhaust.