Installation of Indigo Fresh Water Cooling

This article is copyright 2003 by Ralph L. Vinciguerra. Contact me for permission to use it elsewhere.


The Blue Angel's Atomic Four gas engine (and all A4's for that matter) deserve an upgrade from salt water cooling to fresh water cooling. Running salt water through the engine block causes constant corrosion, and subsequent blockage of cooling passages. This A4 was rebuilt recently, and even after only 3 years of running with salt water has started to become blocked with scale and rust flakes again. I even tried to flush a corrosion preventer into the block after each days run to stave off the damage, but it still wasn't sufficient.

Indigo Electronics makes a nice complete fresh water cooling system kit, and I decided to try and fit this system into the engine compartment. I also sprang for the adjustable thermostatic control, that allows closed-loop temperature control. No more fooling with automotive-style thermostats in the engine head.

To get started, the engine needed to be flushed and cleaned out, so after an initial flush through with Marsolve (a non toxic solvent), the water galley side plate was removed. Look at the strange deposits on the back of the side plate! Also note the extensive salt water corrosion of the side plate where the water worked under the gasket. Running salt water against unprotected iron is a "bad thing". The salt water was killing this fine old iron genny! The hard part is deciding to spend the money to get this worthy system upgrade.

Here's a couple peaks inside the water galley. Note the wierd deposits and scale. Down in the bottom, (I was too dirty at the time to take pictures at the time), there's about an inch thick layer of sandy black rust deposits piling up. Also note the water passage between the center cylinders. This was being blocked at the lower levels. The camera makes the engine paint and the rust deposits look the same color. In reality, the engine paint is pretty, and the rust is ugly. Really.

Here's a new couple views of the water galley, after flushing with Marsolve and scraping, and then fresh water flushing with a hand pump. It took a while to drive all the debris out of the lower areas. That pipe coming out to the lower left leads to a small radiator-style drain cock. This has been handy to drain away some of the debris as it was building up, but it couldn't keep up.

Here's the cleaned and smoothed side plate ready for reinstallation with permatex gasket sealant. There was enough corrosion that the possibility of a leak was worrisome. Also, once clean antifreeze is circulating in the A4, this plate should never need to be removed again. A non-hardening permatex sealant was used.

Now that the cleaning was complete, its time to place the new heat exchanger and the updated plumbing. The exhange fits very nicely is this open space just to the starboard of the A4. Also, that's the optional advanced thermostatic control (adjustable!!) attached to the aft end of the heat exchanger. It controls the mixing of hot and cool antifreeze that is fed into the A4. The exchangers included metal straps fit perfectly against the starboard wall edge, secured with a couple lag bolts. Also, that yellow valve handle at the bottom is a nice low point in the antifreeze loop coming out the bottom of exchanger. This will be used to drain the coolant during flushing.

I also took this opportunity to replumb the entire system starting at the through hull intake. The red handled valve is the new main intake valve, placed immediately after a 90 degree street elbow. I wanted to keep the valve as close to the hull entry point as possible. By using the elbow, I managed to tuck the successive plumbing elements right along the hull down low, preserving splace alongside the A4 to allow future access for maintenance. After the value, is a T, with one hose barbed connector to lead to the new salt water intake pump. The straight part of the T then leads to another value and another open hose barb connector. This is a special purpose access intake for flushing, or in an emergency a hose can be attached and used to drain the bilge!

This is the first test setup to verify the two pumps are working. Each subsystem (salt water and fresh water) is drawing from, and returning to it's own bucket. This is when I discovered that the old engine pump with a new impeller was working poorly. Apparently the new impeller was slightly narrowed than the original and causing leakage around the vanes. I put the old impeller back in and things are working nicely now. That green anti-freeze is "Low Tox", a propylyene glycol formula that's environmentally safe.

After running for about 20 minutes, I disassembled the temporary filter in the anti-freeze loop, and discovered some interesting sludge caught by the polyester filter patch; it was white originally, now it's dark gray. A quick rinse, a new filter patch, and back to testing.

The job is done! Here's the complete installation after numerous hours of tinkering. Valves that should not normally be used are tied off for safety. All the extra valves support special operations like winter prep, and flushing. There's that temporary filter (the long silver assembly at the back of the engine) that cleans the anti-freeze coming out of the exhaust manifold, before it enters the "sparkomix" temperature control valve. The new sea water pump is down behind the alternator.

From further away, you can see the anti-freeze overflow tank. I placed it outside the engine compartment for 2 reasons: easy to fill, AND I can always keep an eye on the fluid level. If the anti-freeze loop ever develops a leak in a hose, or leaks through the head gasket into the cylinders, it should be evident by the level in this tank in plain view. Form follows function; after all this work, it now looks attractive!

A larger image with text labels, and a Diagram are also available for your viewing pleasure.


Blue Angel