3116 and 3126 Marine Engines Caterpillar

Corrosion in sea water circuits can result in premature deterioration of cooling system components, leaks, and possible cooling system contamination. The corrosion may be caused by the lack of zinc rods in the sea water system.

Zinc rods are inserted in the sea water cooling system of the engine in order to help prevent the corrosive oxidation that is caused by sea water. The reaction of the zinc to the sea water causes the zinc rods to oxidize rather than the cooling system components. Rapid deterioration of zinc rods may indicate the presence of uncontrolled electrical currents from improperly installed electrical attachments or improperly grounded electrical attachments.

The zinc rods must be inspected at the proper intervals. The zinc rods must be replaced when deterioration occurs.

Inspect the Zinc Rods

The zinc rods are red for easy identification. Table 1 shows the locations of the zinc rods and the quantities of the zinc rod:

Table 1

Locations of the Zinc Rods
Location	Quantity
Heat Exchanger	3
Transmission Oil Cooler(1)	2
Exhaust Elbow(2)	1
Aftercooler(3)	5

(1)	Zinc rods will only be located in marine transmission oil coolers that are cooled with sea water.
(2)	Exhaust elbows that are aftermarket may or may not be equipped with zinc rods.
(3)	3126 Engine Only

1. Remove the zinc rod.

2. Inspect the zinc rod.

   Ensure that the zinc rod will remain effective until the next scheduled inspection.

   1. If the zinc rod has deteriorated excessively, install a new zinc rod.
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      Illustration 1	g00481100

   2. Tap the zinc rod lightly with a hammer. If the zinc rod flakes, install a new zinc rod.

3. If the zinc rod will be reused, scrape the layer of oxidation from the zinc rod before installation. The layer of oxidation reduces the effectiveness of the zinc rod.

Replace the Zinc Rods

1. Unscrew the old zinc rod from the plug.

   If not enough material remains or the zinc rod has broken off, drill the old zinc rod from the plug.

2. Clean the plug.
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   Illustration 2	g00480345
   (1) Shoulder of the zinc rod (2) Threads of the zinc rod (3) External threads of the plug

   Note: DO NOT apply adhesive or sealant to threads (2) of the zinc rod.

3. Apply 9S-3263 Thread Lock Compound to shoulder (1) of a new zinc rod. Apply the compound ONLY to the shoulder of the zinc rod. Install the zinc rod onto the plug.

4. Coat external threads (3) of the plug with 5P-3413 Pipe Sealant. Install the zinc rod. Refer to the Operation and Maintenance Manual, "Torque Specifications" topic (Maintenance Section).