Steam in the Exhaust: Our First DIY Engine Repair

Last Friday, after deciding to abandon our anchorage at Smuggler’s Cove on Santa Cruz Island, we started the engine, weighed anchor, and got underway for Prisoner’s Harbor on the other side of the island.

As we increased the throttle, we noticed something troubling: Our exhaust was white.

Now, forget any mental images you have of tugboats belching out black smoke or ships puffing white from their stacks. A modern marine diesel, just like a car, should have invisible exhaust.

White exhaust can be either smoke or steam, and each one has a number of possible causes. With help from Peter Compton’s Troubleshooting Marine Diesels (my favorite quick reference; Nigel Calder’s book is my favorite slow one), we decided our white exhaust was likely steam. And there are many causes for steam in the exhaust—but the most common one is a shortage of cooling water.

(OK, time for a quick lesson on marine diesels. All engines generate heat. Cars, trucks, and motorcycles have no choice but to cool the engine with air. But boats are surrounded by cool water, which can be pumped through the engine to remove most of the heat.

If there’s not enough water being pumped through, it’s a problem. And if it gets bad enough, the engine’s heat has nowhere to go—the engine overheats and must be shut down. But in our case, some cooling water was getting through (just not quite enough) so the existing water was being superheated and turned into steam. And there you go: Steam in the exhaust.)

Back to our already-stressful sunset trip from Smuggler’s to Prisoner’s: Since the engine was not overheating (just steaming), we decided to continue on and deal with the problem when we got to our new anchorage.

The first thing I checked was the sea strainer. This is a mesh basket, like a collander, that prevents seaweed and other debris from getting into the engine. It was pretty well clogged up, so I was optimistic that I had fixed the problem.

The next morning, somewhat rested after a rolly night at anchor, we fired up the engine—and everything seemed good. Success! But when we got underway and increased the throttle, the steam was back.

We continued on (toward Los Angeles), going slow to avoid overheating the engine. But my anxiety got the best of me. There were a few more engine components I wanted to check, and we started to think of places we could stop to do some more troubleshooting.

We were torn: We could continue, and it would probably be OK, but it’d be a long day since we had to go slow. Or we could stop, which would take time, but if we fixed the problem, we could go fast! And at least we’d know what was going on.

So we pulled into Scorpion Anchorage (Santa Cruz Island has the nicest sounding bays). I opened up the seawater pump (which pulls cooling water into the engine) and inspected the rubber impeller. It was fine.

The next step was to check the intake itself—the hole in the hull where cooling water is sucked into the boat. Time to go swimming. I set up a safety line, jumped in the water, put on my mask, and dove under the boat to check the intake for obstructions. It was also fine.

Ready to dive the boat and check the engine cooling water intake.

I gave myself a quick rinse (with hot water!) and we got underway again. But since we hadn’t fixed the problem, I was disappointed. And there was one still more place to check—the section of hose between the intake and the strainer—but it wasn’t something I wanted to tackle at sea.

So we limped to Los Angeles, going slow and holding our breath.

The next day I removed that section of hose and looked inside. A ha! I found some chunks of styrofoam and a few blades of kelp. With all of this debris in the hose, it’s a miracle that any water was getting through.

It was a big relief to find (and fix) the problem, but as our friend Mark (from s/v Windward Passage) reminded us: “It’s not usually that easy.” He is right. We were lucky.

And finally, since this wouldn’t be a proper Particular Harbor post without a cat photo… here are two pictures of Guinny helping me take apart the seawater intake.

“Whatcha doin’?”

“Here, let me get a closer look.”