Volvo MD2030D Heat Exchanger - oopsie

You know what a boater doesn’t like to hear – their bilge pump going off. The bilge pump, non-boaters, takes water that has somehow worked its way inside the boat and pumps it out of the boat. This water could be something relatively innocuous like interior humidity condensing and dripping into the bilge until it reaches a level that triggers the pump. Or it could be something of moderate concern like a leaking point in the deck of the boat. Or it could be something of major concern like a hole in the boat.

When we go away from the boat for a few weeks the bilge dries out, completely, even if it is raining. This tells us that we don’t have any deck leaks (or none big enough to get any real water) and the only water we get is condensation. Our condensation water doesn’t accumulate in enough quantity to cause the bilge pump to go off.

So, imagine our distress when our bilge pump went off twice in a very short period of time, while we were under sail, in a narrow channel near Tofino. We had been revving the engine a bit while exiting a harbor to check our speed instruments (how fast we are going in the water vs. how fast we are going over ground). We put up the sails and started sailing in relatively light air. The bilge pump went off. I check under our floor panels and saw a tiny trickle of water coming from the back of the boat. We figure that jostling the boat around caused pockets of still water to run into the bilge. I open the engine compartment – looks fine.

But, not long later, it went again. I check the bilge and engine and see a puddle of watery orange liquid under the engine. Our coolant…very diluted with water.

Carol takes the watch and I start grabbing books off the shelves, looking at my diesel engine repair notes, troubleshooting by putting my hands on various parts of the cooling system to see if there is a cold spot (blockage or failed sensor/valve). Carol calls our mechanic who says that the most likely problem is a pinhole leak in our heat exchanger which means that we have saltwater in our engine. Not good for its longevity.

We switch places. Carol goes down and begins exercising his navigation skills and I go up and exercise my short tacks in heavy wind skills because, of course, the wind has built up considerably. This is a good thing actually because it means that we know we can make way under sail and won’t end up drifting into land. It also means several hours of tacking every 5 minutes so we can make our way to Tofino. We ran the engine for the last few minutes as we entered the tricky back channel to the anchorage and dropped anchor.

After some further advice by phone, very kind offers of help from fellow boaters via the SSB who offered to drive us places and suggested possible fixes, we found (via some internet searching) that the black cuff (you can see it hanging loose with two blue round hose claps dangling from it - below left) which directs sea water through the tubes sometimes comes unseated allowing salt water to go on the outside of the heat exchanger, adding volume to the coolant, which then comes out of the pressure release tube. PLUS, this salt-water coolant is now circulating in your engine. Some engines are designed to be cooled internally by saltwater, but most modern engines are not and the salt water can seriously damage the engine if allowed to sit. The biggest problem is when people don’t know salt water has entered their engine and don’t flush it and their engine corrodes internally. The only thing holding the cuff in its seat are the two hose clamps.

 

For the non boaters, who know something about cars, the heat exchanger is your radiator except that the coolant is cooled by sea water pumped through the heat exchanger rather than air pumped over the radiator. That sea water is supposed to stay inside of these long skinny tubes while the coolant bathes around them in the larger radiator tank.

As you can see below the sea water causes a build up inside the heat exchanger (our build up is actually very mild, our engine is relatively young, and was easily flushed out). Eventually corrosion causes pinhole leaks (or larger cracks) in one or more tubes. Depending on the manufacturer they will tell you what percentage of tubes you have to have for the engine to work effectively. If one or two tubes crack you can often have a welder plug those tubes which means the heat exchanger doesn’t cool the coolant as well, but stops sea water from entering your coolant through the cracked tubes and thus entering your engine. This build up is also a problem for circulation and that is why you flush and clean your heat exchanger.

 

Why did ours fail? The hose clamps were loose and when we revved the engine we wiggled them further loose. Why didn’t we tighten the hose clamps? Somehow the existence of a thick layer of Volvo paint over them caused me to ignore their presence, as simple as that. Simple and stupid. I’ve checked the hose clamps on every other inch of our boat and yet two of the easiest to check I didn’t check because they were covered in paint. Oy.

We flushed the engine, ran it and tested the new installation. Flushed it again…and flushed it again. Many engine hours later, everything is running smoothly.

In the midst of the crisis, with the knowledge that the most common problem is a leak in the core (it is the most likely thing, our experience not withstanding), we bought a heat exchanger insert for an exorbitant sum so now we are also the proud owners of an expensive spare part.

Welcome to boating :)

((This occurred in August 2010))