Friday, February 3, 2012

A Girl's Guide to Diesel Engines: The Octopus in Our Water Intake

That's our water strainer. Not pretty.

Engines are finicky things. They have to be hot enough to start up, but they can't get too hot or else they self-destruct. Raw seawater in conjunction with fresh water keeps the engine cool. Because you don't want salt water corroding the inside of your engine, some marine diesels use a heat exchanger, much like a car's radiator, where the fresh water and the seawater are able to run past each other. The seawater cools the freshwater, which cools the engine without corroding it.

Here's how the basic system works. The seawater comes in through the seacock, then goes through a strainer to the raw water pump, which pumps the seawater through the heat exchanger. Then, the seawater dumps overboard through the exhaust. If you don't have water coming out through the exhaust, that spells B-A-D-N-E-W-S. 

The above situation is exactly what kept happening to us. For some reason, seawater wasn't coming in to cool off the engine, and we'd be greeted with the dreaded screech of the engine overheating alarm, a truly ear piercing experience. Obviously, something was impeding our water flow, and obviously that something had to be an octopus. What other conclusion could sensible people come to?

So, in order to banish the octopus, we cleaned out the entire system starting at the seacock. We cleaned the strainer, checked the water pump and the impeller and flushed out the heat exchanger. Our friend Raymond was even nice enough to don a wetsuit and scrub the thru-hull with a bottle brush. Thanks, Raymond, and sorry about the cold water! And there was some not nice stuff floating around in our water intake system. A few other people we spoke with about the water issue said they had also had problems in Galveston Bay, especially with little mullet fish getting caught in the strainer. I guess that's probably what the octopus was eating.

Now our water flow is the best it's ever been, and no more overheating alarm! We never actually saw the octopus, but since the water is now coming through like a champ he has definitely moved on. It's that whole correlation and causation thing. Obviously.


  1. An invisible octopus in the exhaust.....that's a bad night out.

  2. "It's that whole correlation and causation thing. Obviously."

    Oh of course!

    Oh the joys of boat ownership... I can't wait!

  3. I've got to admit, it's pretty fun to own a boat. Plus, you get to pretend that you have an octopus living in your house. Can't do that on land!

  4. Well, an octopus is a really good excuse for having trouble with the water intake. I keep reading about how people go into the water to check on these things. Brrrr. I fear a wetsuit may be on our list of 'to gets' for the future.
    We are well familiar with the whole water intake-engine overheating alarm thing. And impellers. We're really familiar with those. Mike found a good source for our ancient Westerbeke and we keep a few on hand. He's getting pretty good and changing them out quickly. Is that a skill we really WANT to have to be good at? You haven't lived until your engine alarm goes off in light wind, close to dangerous rocks. Boy howdy, that's some fun!
    Keep up the good work on these Girl Guides. I love it. I need it.

  5. I hope we never have to hear the overheating alarm near rocks, but that's wishful thinking, no doubt. Just the thought gives me chills.

    Ah, the impeller. I've helped Vlad change ours out once, but man, is it a pain to get to. Come to think of it, I'm probably shooting myself in the foot with this whole "learning how to fix an engine" thing!

  6. The overheating near rocks has happened to us on a number of occasions. It certainly gets the adrenaline pumping, I can tell you. And you can hear some mighty creative words coming from the cabin, too. On the other hand, I'm really handy when it comes to light air sailing! You learn very fast when the rocks are looming.
    Yes, you very well might be shooting yourself in the foot learning about engines, but just think of all the guilt you won't feel when you are helping Vlad change those damaged impellers. That will be worth it. Good times!