We monitor a few online forums and try to help out where we can. Recently a few questions came up on the Great Loop forum about zincs for your engine and what to do about the occasional pieces of zinc that break off, possibly blocking water flow through the heat exchanger. That’s usually as simple as popping a new one in. The old zinc – operative word old as in used up – often will crumble with the force of the new zinc replacing it. But you may have to take off the end cap on the heat exchanger and remove the debris using your fingers or even some long tweezers.
So let’s talk about what a pencil zinc looks like and where to find them on your engine….yup, them as in more than one zinc to find.
Most propulsion engines with raw water cooling have heat exchangers. Think of this as a water cooled radiator.
Just like a radiator there are tubes inside the shell or housing. Anti freeze or coolant runs between the tubes and raw water, fresh lake water or salt water run inside the tubes. This is the conductive cooling method needed to cool the coolant or oils in the engine.
Because the tubes are silver soldered into place, and this soldering is a softer metal than the tubes themselves, you must protect the solders from being eaten away and causing a fluid leak. Either raw water leaks into the engine system or engine fluids leak out into the raw water and out the water cooled exhaust.
The way to find the zincs on your engine is to look at the heat exchangers and locate an unpainted hexagonal or square brass bolt head. Chances are this is your pencil zinc.
When you unscrew it raw water may drain out depending on elevation above water line of your boat.
The many locations you may have pencil zincs include coolant heat exchanger, reduction gear transmission oil cooler, air cooler after the turbo charger and possibly an active fin stabilizer cooler. You may have more coolers than I described here but chances are they are not zinc protected.
Generators may not have zinc protection in their heat exchangers.
Ideas on how many zincs per engine?
- Some Caterpillars have 3 in the coolant heat exchanger, 2 in an air cooler and 2 more in a fuel cooler.
- Cummins may have 2 in the coolant heat exchanger and 2 in the turbo after cooler.
- Perkins just has one located in the coolant heat exchanger.
- You can see no two engine brands have the same amount of zinc protection in their designs.
- BTW, you can purchase engine zincs from most boat stores.
Read the engine owners manual, ask your mechanic where the zincs are located and attend a DIY boat owners maintenance class. (and check out an older story with a few more photos right here)
Do you know how to change dirty fuel filters and replace failed raw water pump impellers? Do you have correct spares onboard?
Ask Captain Chris this and so much more at our seminar Introduction to Boat Systems. Learn more here about when and where you can attend our next program.