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This page updated:
March 2011


BoatSafe's "Engine Cooling Systems Explained"
Engine cooling system articles in DIY Boat Owner magazine issue 2000 #1.
"Keeping It Cool" by Don Casey in 1/2001 issue of Blue Water Sailing magazine.
Article by Ed Sherman in 9/2001 issue of Cruising World magazine.
Don Casey's "Replacing a Cooling Pump Impeller"

Speedseal: quick-release cover for cooling pump impeller. And I didn't realize at first: the best thing about it is that the bolts are retained by the cover, so you can't drop them into the bilge.

From Stuart Burgess:
Inserting new impeller:

You don't have to have the vanes facing the right way. The first time the engine turns will spin them into position. Here is the easy insertion method:

Lube the new impeller with silicon lube, and then tie an electrical cable tie around it until it is formed into a slightly smaller shape than you need to insert. Push it in and the cable tie will slide off as the impeller goes into place.
I couldn't find a cable-tie strong enough to compress my 12-vane impeller.

Installing a hot water heater in the engine coolant loop,
from Shaun Sweeney on IRBS live-aboard mailing list:
... Install a coolant filter in the line.

... The coolant filter can be picked up at any good truck supply shop and comes in two varieties - cheap and expensive. The cheap ones are recommended for starters as you'll find they plug up quickly if your engine is not new. The more expensive ones help keep the pH level and are selected based on your tests of pH. You won't find a diesel truck on the road today without a coolant filter so why don't we find them in more boats? ...

From Norm on The Live-Aboard List:
Cleaning your strainer every week in the Tropics is not at all unusual. When anchored in Key West I cleaned mine, mostly plugged with marsh grass, every two days.

Several points:

Remove the slotted strainer on the outside of the boat. Don't even bother with it because you have to go under water to clean it.

Connect the strainer and the seacock with about a foot or so of hose. You can pull the hose off the strainer and then ram a piece of PVC pipe (capped at the inboard end) through the hose, seacock, and thruhull to rod it out.

Get a strainer with a good solid monel basket so you can clean it. The bigger the strainer, the less often you have to clean it.

Arrange the output hose to the pump straight too, and the manifold, so you can rod it easily.

The idea is that you are going to have to rod out these passages periodically so set up your system to make it easy.

You could also try setting up an acid rinsing system for the hard to rod sections. Something you can set up and use just by putting a 5 gallon bucket of acid solution in place with two hoses in it then set the valves and run the pump to circulate the acid mix through the system. You cannot acid clean the input seacock so you will still have to rod that. But the acid can clean the places you cannot rod.

You could install air-cooled condensers.

The bottom line ... the seawater lines are going to foul, there is nothing you can do to stop it. The only thing you can do is to make it easy to evict the squatters.
From John / Truelove on The Live-Aboard List:
I have never had problems like this, even when we were in that nasty, shallow water in the ICW and its tributaries. And, I don't recall ever finding much in the strainer basket. The inside of the seacock has always been clean, too, probably because we paint with AF as far up as we can reach.

Maybe our intake is deeper and so doesn't get the growth. At any rate, I strongly disagree with removing the slotted strainer on the hull, unless you want to fill your piping and strainer with baggies and jellyfish.

So there you have it ... two widely differing opinions!

Cleaning the heat exchanger, from BT on Cruising World message board:
Here is what a radiator shop guy told me: Get some CLR which is sold at places like ACE Hardware and Echard's. Use that to clean the fresh water side. Use it outdoors because the gas it makes is poisonous. Get some swimming pool acid which you get at the swimming pool supply store. Use that to clean the salt water side. Worked great for me.
From SlowButSteady on Sailnet forums:
A word of caution: using chemical engine flushes can sometimes break stuff loose w/o completely dissolving it, particularly in engines with a lot of crud in them. These undissolved bits can clog smaller channels in the engine, or more likely in the heat exchanger, causing problems much larger than having the original deposits. If you can do so w/o danger of getting water into places it really doesn't belong, I would try back-flushing the system (you will have to remove the impeller) after such a treatment to make sure there aren't any such clogs.

From Norm on The Live-Aboard List:
Install a strainer. I have one of those little blue Rule strainers sold to install in the domestic sweet water suction line, at the outlet of the seawater pump. When (not "if") the blades on the pump's impeller disintegrate, the pieces will be visible and easily removed from the strainer. MUCH easier than disassembling the downstream parts to clean out all the many bits of rubber. Experience speaking here ...

And while you're at it, put some kind of shield around the seawater pump shaft area (I use duct tape), so when (not "if") the seal starts leaking the water won't be sprayed into the nearby alternator.

From Bob Clinkenbeard on The Live-Aboard List:
... not all heat exchangers have zincs installed. ... people have added pencil zincs to their exchangers by drilling and tapping a hole in the end cap where it doesn't interfere with the tube bundle inside. ...

Some engines have a lot of zincs: pic.

From article by Ed Sherman in 9/2001 issue of Cruising World magazine:
A bad engine ground can cause electrical current to flow through your cooling system. This can destroy the corrosion-inhibiting properties of the coolant.

To check for this problem:
  1. Turn off all AC and DC systems.
  2. Attach negative probe of voltmeter to battery negative post.
  3. Dip tip of positive probe of voltmeter into coolant in reservoir and check for AC or DC voltage; both should be zero.
  4. Turn on AC circuits one at a time and check voltages. Never should see more than 0.3 volts.
  5. Do same for each DC circuit.
  6. Close coolant cap, attach positive probe to engine block, and check each circuit again, one at a time.
  7. Leave positive probe attached to engine block, crank engine for a few seconds without starting, and check DC voltage while cranking.
  8. Leave positive probe attached to engine block, start engine, and check each circuit again, one at a time.

Any problem found likely is due to either a corroded connection or an undersized cable.

Idea: would be nice to have a transparent cover on the raw-water impeller, so you could inspect it easily. But I've never heard of such a thing. Would have to be high-temperature-tolerant and abrasion-resistant material.

From article by Don Casey in 4/2006 issue of Sail magazine:

From Brett in Benner Bay:
If leak from fresh water (antifreeze) coolant system into oil system, drain both systems and refill both with oil (lightest possible is best in coolant system). Engine will run a bit hot, but leak will now be harmless.