D346 MARINE ENGINE General Caterpillar

1.1. Safety Precautions
2.1. Cold Weather Starting
3.2. Glow Plugs (Attachment)
4.2. Starting Fluid
5.2. Air/Fuel Ratio Control with Over-ride
6.2. Jacket Water Heater (Attachment)
7.2. Dipstick Oil Heater
8.1. Engine Horsepower Ratings
9.2. Continuous and Prime Ratings
10.2. Intermittent Pleasure Craft Rating
11.2. Standby Rating
12.1. Pre-Start Checks And Procedures
13.1. Priming The Sea Water Pump
14.2. Centrifugal Sea Water Pump
15.2. Rubber Impeller Pumps

Proper engine operation and maintenance are essential for long engine life and maximum performance. The basic operation and periodic maintenance procedures are outlined in this OPERATION GUIDE. Before starting the engine, familiarize yourself with these procedures.

Your AVSpare dealer is available for troubleshooting, testing and servicing when required.

Safety Precautions

Safety is basically common sense. A general guide of safety precautions may be listed, but each installation has its own peculiarities which cannot always be predicted and covered by rules. Past experience and common sense are needed for the necessary safety measures. Lack of attention to safety can result in serious accidents. Be alert. Watch for hazards. Use preventive measures. Correct deficiencies promptly.

The following safety precautions are a guide to safe operation:

1. All electrical equipment must be grounded according to Coast Guard regulations.
2. Install guards over all exposed rotating parts. If guards are missing, inadequate or in need of repair, have corrective measures taken.
3. Wear ear protective devices if working inside an enclosed engine room with the engine running.

4. Wear a safety hat when working in the area of overhead equipment.
5. Do not wear loose clothing whenever working around engines or machinery.
6. Keep the engine room and deck clean. Wipe up spilled oil or fuel.
7. Provide adequate waste oil disposal.
8. Keep batteries in a well ventilated area. Hydrogen gas, which is present in the area of the batteries, is highly explosive.

9. Do not smoke around batteries.

10. Store oily rags in containers. Don't leave rags on an engine.
11. Remove all tools and electrical cords from the engine before starting.
12. Disconnect and tape the ground battery lead before working on an engine. Be sure an automatic start-stop system cannot operate and start the engine while working on it.

13. Never start, nor attempt to run, an engine with the governor linkage disconnected.

14. Never try adjusting or repairing either the engine, or the driven equipment, while the engine is running.

Cold Weather Starting

Many variables can affect cold weather starting. Use the above chart as a guide, but actual experience will determine when aids are necessary and how they should be used. The following starting aids are available.

Glow Plugs (Attachment)

Use glow plugs before cranking the engine, immediately after the engine has started, and until the engine is running smoothly.




1. Push in and turn the HEAT-START switch to the HEAT position and hold for the approximate heating time shown in the Cold Weather Starting Chart.

2. Turn the HEAT-START switch to the START position.

3. As soon as the engine starts, turn the HEAT-START switch to the HEAT position. Hold the switch in this position until the engine is running smoothly.

4. Release the switch.


Never use glow plugs when the engine is warm and running.

Starting Fluid


Spray starting fluid only while cranking the engine.

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

Starting fluid is volatile and must be stored away from heat and direct sunlight. If an aerosol container is used, follow the instructions on the container.

1. Heat the glow plugs for the approximate heating time shown in the Cold Weather Starting Chart.

2. Turn the HEAT-START switch to the START position. While cranking, discharge a spray of starting fluid into the air inlet or air cleaner.

3. If necessary, repeat the procedure.
4. After the engine starts, it may be necessary to return the HEAT-START switch to the HEAT position until the engine runs smoothly. Then release the switch.

Air/Fuel Ratio Control with Over-ride

The large V-type engines are equipped with an air/fuel ratio control which has an over-ride lever. During extremely cold weather, more fuel and a richer fuel mixture may be necessary when starting.

If the engine is blowing white smoke, but will not start:

1. Release the start switch.
2. Move the over-ride lever to the START position.

3. Use starting aids and crank the engine.

As soon as the engine starts and runs, the lever will return to the RUN position.

Jacket Water Heater (Attachment)

In very low temperatures, the lubricating oil must be warmed to allow starting. A jacket water heater maintains jacket water temperature at approximately 90°F (32°C). The warm jacket water will keep the oil in the upper part of the engine block warm enough to flow while starting.

Dipstick Oil Heater

Contact your AVSpare dealer before installing a dipstick crankcase oil heater.

Engine Horsepower Ratings

There are two general horsepower ratings for marine engines and two for electric set engines. They are intermittent pleasure craft or continuous; and standby or prime, respectively. These ratings are the recommended engine horsepower settings which are based upon the load requirements and the type of engine operation.

Continuous and Prime Ratings

Horsepower settings for these two ratings allow operating a constant load for long periods of time without shortening engine life.

Intermittent Pleasure Craft Rating

Horsepower settings for this rating requires the engine to be operated for periods no longer than 5 minutes at full speed position followed by an equal time, or longer, of operation at reduced speed.


If an engine is set for an intermittent rating and is operated for longer periods of time at constant full engine speed, the engine life will be shortened.

Standby Rating

Horsepower settings for this rating allows the electric set to supply rated power for a period of time, after which the engine is stopped.

Contact your AVSpare dealer if there is doubt as to which rating your engine has.


Horsepower settings should only be done by authorized personnel.

Pre-Start Checks And Procedures

1. Make a "walk-around" check of the engine and components. Correct minor adjustments before they develop into major repair jobs.
2. Check the crankcase oil level. The oil level must be between the ADD and FULL marks on the dipstick. See the LUBRIAVSION AND MAINTENANCE PROCEDURES.



D379 and D398 Engines are equipped with a combination sump pump and prelube hand pump. After a prolonged shut down, or after a filter and oil change, operate the hand pump to fill the lube system oil passages before starting. See the LUBRIAVSION AND MAINTENANCE PROCEDURES for further details.

3. Check the marine gear oil level. Oil level must be at, or just slightly above the FULL mark with the engine stopped. Add oil as required.

4. Check the day fuel tank level. Keep the fuel tank full.

5. Check the engine jacket coolant level. The coolant level must be at the base of the fill pipe with the engine cold.

6. Open the sea water valve.
7. Reset shutoff devices. See the topic ATTACHMENT, Emergency Shutoff Devices and Alarms.
8. Open the fuel supply valve.


The fuel return line must be open to prevent engine damage.

9. If air has entered the fuel system, prime the fuel system. See the LUBRIAVSION AND MAINTENANCE PROCEDURES.

PRIMING PUMP - 4.75" (121 mm) Bore Engines

PRIMING PUMP - 6.25" & 5.4" Bore Engines

10. Disconnect any battery charger which is not protected against the starting motor drain.
11. Place the marine gear control lever in neutral, or open the circuit breaker on a marine generator set.


Do not start an engine under load.

12. Vent the air from the sea water pump suction line. The suction line must be filled with water to allow the pump to prime.

Priming The Sea Water Pump

There are two types of sea water pumps: a centrifugal pump which is used on 5.4" (138 mm) and 6.25" (158 mm) bore engines; and a rubber impeller pump which can be used on all bore size engines. The centrifugal pump must be filled with water before starting; the rubber impeller type pump is a positive displacement, self-priming pump.

Centrifugal Sea Water Pump

1. Before starting, carefully loosen the fill plug on the priming chamber.

If water appears while loosening the plug, immediately tighten the plug: the system is full.

If water is not present, continue removing the plug and fill the system as instructed below.

2. To fill the water system, add water through the priming chamber opening until the chamber is full.


The suction line must be vented to be sure air is not trapped in the suction line. Air in the suction line will cause the pump to lose prime while operating.

3. Close the vent line and install the fill plug.
4. Check for water leaks in the water line and pump. Have repairs made to prevent possible engine damage.
5. Move the governor control to half engine speed position, and start the engine as instructed in the topic, STARTING THE ENGINE.

Rubber Impeller Pumps

If the water lines were drained either for storage, or because of repairs being made to the engine or vessel:

1. Remove the pump cover and gasket.

2. Remove the plate, if necessary.

3. Squeeze, or flow, hand cleaner or liquid detergent between the impeller blades. Do not use a cleaner which contains grit. The purpose of the cleaner is to lubricate the impeller blades before the water is drawn into the housing.

4. Install the plate, if it was removed.
5. Inspect the gasket on the cover. Install a new gasket if necessary. Install the cover.
6. Move the governor control to half engine speed position.
7. Start the engine. This is a positive displacement pump which will prime itself at low engine speed. See the topic, STARTING THE ENGINE.