D346 MARINE ENGINE Caterpillar

Electrical System


Battery Installation

Preparing Dry Charge Batteries

One day before installing a new dry charge battery, add the electrolyte solution to each cell.

1. Fill each cell to the bottom of the vent with electrolyte solution.


If the battery is initially filled with water by mistake, the battery is ruined and must be replaced.

2. Allow the battery to sit for several minutes to permit the battery plates to absorb the electrolyte.
3. Add make-up electrolyte solution until the level stabilizes. Once the level stabilizes, never add anything but water.
4. Install the vent caps.
5. Remove the tape covering the vent hole in each cap.
6. Slowly charge the battery on a battery charger until the specific gravity of the solution is at least 1.240 at a temperature of 80°F (27°C).

NOTE: If the electrolyte solution temperature nears 125°F (53°C) reduce the charging rate. Temperature in excess of 125°F (53°C) will ruin the battery.

Preparing Wet Charge Batteries

The electrolyte solution was added by the manufacturer. Make-up solution must be water; never add electrolyte or acid to a wet charge battery. If necessary, slowly charge the battery before using.

Using A Battery Charger

A desirable charging rate can be calculated by multiplying the amp-hour rating of the battery by .07 (7%).

Shut off the battery charger before disconnecting the booster charger clamps from the battery terminals. While the battery is charging, hydrogen gas is being given off through each vent cap. When hydrogen gas is mixed with air, the mixture is highly explosive and will explode in the presence of a spark or small flame.

------ WARNING! ------

Never smoke near the area where batteries are being charged.


Installing Battery

1. Be sure the tray is free of objects which may puncture the battery case when the hold down straps are tightened.
2. Be sure terminal posts and cable clamps are clean.
3. Place the battery in the tray. Tighten the hold downs evenly until the battery is snug. Do not overtighten.
4. Connect the "hot" terminal first.
5. Connect the ground terminal last.


Always connect the "hot" terminal first.

When the "hot" terminal is connected first, no arcing can occur if the wrench accidentally contacts both the terminal and the frame or tray. The part that is contacted will take the same polarity as the battery terminal.

By connecting the ground terminal first, the frame or tray is connected to ground. Then, if the wrench accidentally contacts the frame while connecting the "hot" terminal, a circuit is completed through the wrench. A hot spark will occur which could burn the person holding the wrench, or possibly explode the battery if an excess of hydrogen gas is present at any one of the vent holes.

After connecting both cables, apply a thin coating of grease over the cable clamps, terminals and hold down fasteners.

Battery Maintenance

Testing The Electrolyte Solution

The general condition of a battery can be determined by measuring the specific gravity of the electrolyte solution and adjusting the reading to 80°F (27°C). If the electrolyte level is too low to allow taking a hydrometer reading, add make-up water to the correct level and then charge the battery 2 to 4 hours before taking a reading.

1. Insert the hydrometer into a cell. Fill the hydrometer barrel while holding it vertically. The float must not drag on the wall of the barrel.
2. Read the hydrometer:

1.250 or above - fully charged battery cell

1.250-1.225 - full to half charged battery cell

1.225-1.150 - half to low charged battery cell

Below 1.150 - dead cell

1.000 - water

3. Test each cell in the same manner.


4. If there is more than .050 (50 gravity points) variation between the highest and lowest reading, the battery should be replaced.
5. Adjust the readings to 80°F (27°C).
a. For every 10F° (5.5C°) the electrolyte temperature is above 80°F (27°C), add .004 (4 gravity points) to the specific gravity reading.

Example: Electrolyte temperature = 100°F; 38°C

Corrected temperature = 80°F; 27°C

Difference: = 20°F; 11°C

Increments: 10; 5.5

20 ÷ 10 = 2; 11 ÷ 5.5 = 2

2 × 4 gravity points = 8 gravity points

Add 8 gravity points to your hydrometer reading to obtain the adjusted reading at 100°F. If the uncorrected hydrometer is 1.240 the corrected reading would be: 1.240 + 8, or 1.248

b. For every 10F° (5.5C°) the electrolyte temperature is below 80°F (27°C), subtract .004 (4 gravity points) from the specific gravity reading.

Example: Electrolyte Temperature = 10°F; -13°C

Corrected temperature = 80°F; 27°C

Difference = 70°F; 40°C

Increments: 10; 5.5

70 ÷ 10 = 7; 40 ÷ 5.5 = 7

7 × 4 gravity points = 28 gravity points

If the uncorrected hydrometer reading is 1.210 the corrected reading would be 1.210 - 28 = 1.182

The corrected reading is of most importance during cold weather when the hydrometer reading is always corrected to a lower specific gravity reading. A low reading signifies the battery has less available power to crank the engine and that booster batteries may be required.

Checking Electrolyte Level

Check the electrolyte level of each cell and the general condition of the battery.

1. Maintain the electrolyte level to the base of each vent well.
2. The make-up water must be one of the following (in order of preference):
a. Distilled water.
b. Odorless, tasteless drinking water.
c. Iron free water.
d. Any available water.

------ WARNING! ------

Never add acid or electrolyte.


Reading The Ammeter

1. After starting the engine, the ammeter indicator should register to the right of zero, but should never be "pegged".
2. After the engine has been running, the indicator should be just to the right of zero.

If the indicator either "pegs" to the right, or remains to the left of zero with an increase of engine speed, have the electrical charging system checked.

The alternator charging rate maintains the battery's electrolyte specific gravity reading, and the battery's performance. An undercharge rate cannot maintain a desired 1.250 specific gravity reading. An overcharge rate will boil the water from the electrolyte solution. A proper charging rate should require no more than one ounce (30 cc) of water per cell per week to maintain a fully charged battery.

Cleaning Battery

1. Mix a weak solution of baking soda and water. Apply the solution with a bristle brush.


2. Thoroughly rinse the battery and battery tray with clean water.
3. Apply grease to the battery cable clamps and terminals and to all threads.

Cold Weather Battery Maintenance

The following instructions aid in obtaining maximum performance in cold weather:

1. After adding make-up water, charge the battery.

The added water will dilute the electrolyte. This will lower the specific gravity of the solution, raise the freezing point of the solution and lower the charge of the battery.


2. Keep the batteries fully charged either by operating the charging system or by using a battery charger.
3. Keep the electrolyte warm when the battery is not in use. The heat from an electric light bulb usually is sufficient.


Do not lay cloth or any flammable material in contact with a lighted bulb. Charring, or fire, can result.

4. Use starting aids as instructed when starting.
5. Use booster batteries as required. Connect as instructed below.

Connecting Lower Voltage Batteries In Series For Booster Starting

To obtain 30 volt starting, connect five 6 volt batteries in series as illustrated below.


To obtain 24 volt starting, connect four 6 volt batteries in series as illustrated below.


To obtain 24 volt starting, connect two 12 volt batteries in series as illustrated below:


1. Using jumper cables, connect fully charged batteries in series: Connect the positive terminal of one battery to the negative terminal of a second battery.
2. Using a pair of jumper cables, connect the red jumper cable to the "hot" terminal of the booster batteries.
3. Connect the black jumper cable to the ground terminal of the booster batteries.


Keep the red and black cable terminals from touching each other.

4. Connect the other end of the red jumper cable to the "hot" terminal of the engine batteries.
5. Connect the other end of the black jumper cable to the ground terminal on the starter motor. DO NOT connect this cable to the engine frame.
6. Start the engine using starting aids as instructed.

Removing Jumper Cables

As soon as the engine starts:

1. Disconnect the black jumper cable from the engine battery ground terminal.
2. Disconnect the red jumper cable from the engine battery "hot" terminal.
3. Disconnect the black jumper cable from the booster batteries.
4. Disconnect the red jumper cable from the booster batteries.
5. Disconnect the booster batteries. Charge them to full capacity with a battery charger.

Charging Alternator

Checking Alternator Belts

1. Check belt wear.
2. Apply a 25 pound (11,34 kg) force, perpendicular to the belt, midway between the driver and driven pulleys. Measure the belt deflection.


3. Proper belt deflection is 9/16 to 13/16" (14 to 20 mm). Adjust the belt tension as required.
4. If one belt in a set requires replacement, always install a new matched set of belts-never replace just the worn belt. If only the worn belt is replaced, the new belt will be carrying all of the load-as it will not be stretched as much as the older belts-and all of the belts will fail in rapid succession.

Adjusting Alternator Belts

1. Remove the belt guard.
2. Loosen the alternator mounting bolts.
3. Push the alternator outward until the belt is properly adjusted.
4. Tighten the mounting bolts.
5. Check the belt adjustment.
6. Install the belt guard.


Glow Plugs

Testing Glow Plugs

1. Stop the engine.
2. Disconnect the lead harness wire from the magnetic switch.
3. Connect an ammeter of sufficient capacity between the magnetic switch terminal and the lead harness wire.
4. Push in, turn and hold the HEAT-START switch in the HEAT position.
5. The ammeter reading should be approximately equal to the number of glow plugs multiplied by 5, the approximate amperage used by each glow plug.

A deviation of 5 or more amps from this reading may indicate one or more defective glow plugs.

Locating Defective Glow Plugs

1. Push in, turn and hold the HEAT-START switch in the HEAT position. Observe the ammeter reading.
2. Pull the lead from a glow plug. Observe the ammeter reading.

NOTE: If the ammeter reading does not change, the glow plug was not drawing current when connected and can be assumed to be defective. If the ammeter reading decreases, the glow plug is working properly.

3. Release the HEAT-START switch.
4. Connect the lead to the glow plug.
5. Test each glow plug individually.

Installing Glow Plugs

1. Disconnect the lead wire at the defective glow plug.
2. Remove the defective glow plug.
3. Apply anti-seize compound to the threads of the new glow plug.
4. Install the new glow plug and tighten to a torque of 10 to 12 pounds feet.
5. Turn the HEAT-START switch to the HEAT position and observe the ammeter reading.
6. Release the switch.
7. Install the lead wire.
8. Turn the HEAT-START switch to the HEAT position. The reading should be increased. If the reading is the same, check the glow plug wiring.
9. Disconnect the ammeter.
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