Reprinted by permission of

by Hugh Straub

I guess I'm not much of a sailor. After racing in doldrums for a large part of my life, I find irresistible joy in turning to my reliable Atomic 4 whenever my GPS reads less than 4 knots. A friend gave me a drifter for my Easterly 30, but I gave it to someone very much more committed to wind power than I. So you will appreciate my consternation as I watched, over a period of months, the normal operating temperature of my ancient, raw­water-cooled auxiliary climb from the optimum 150' to 165°F. Some might say the temperature increase is normal, considering Lake Ponchartrain water temperature ranges from below 50°F in winter to more than 9O°F in late summer. And they have a point.

My Atomic 4 has a manual thermostat. I removed the spring-loaded automatic thermostat that never seemed able to cope with our lake's temperature fluctuations, and I installed a simple manual valve in its place. The thermostat (whether automatic or manual) works by
opening a cooling­water bypass line. When the engine is cold, the bypass is open and cooling water bypasses the engine block and head. As the engine warms, the thermostat gradually closes the bypass line, forcing cooling water through the block and head. The 140'F thermostat recommended for raw-water operation starts opening at its rated temperature and generally should keep the engine temperature in the 150° to 160°F range, which is the maximum allowable temperature to minimize the precipitation of certain seawater minerals in the cooling passages.

  Manual valve
For long motoring passages, I simply adjust the manual valve in the bypass line to get precisely the needed cooling to maintain the preferred temperature. (The acknowledged Atomic 4 guru, Don Moyer, recommends against removing the automatic thermostat even if a manual valve is installed in the bypass line. I've not followed his advice on this point and to date am pleased with my arrangement.)

But, lately, instead of my usual precise temperature control, the engine temperature had been rising, and I guessed it was time to clean the engine-
  cooling passages. I needed to clear away the accumulated rust scale, mineral deposits, and assorted crud that was insulating my engine from the meager cooling capability our hot lake water otherwise provides. Here's how to do it.

The plan is to introduce fresh water mixed with muriatic (hydrochloric) acid into the inlet side of the engine and remove the water/acid/crud-laden mix from the cooling-water discharge at the engine-exhaust manifold.

Close the cooling-water through­hull valve. Locate the water pump. See the hose leading from the pump to the