The CJ-3A Information Page | The CJV-35/U Page

CJV-35/U Underwater Ventilating System


CJV-35/U 10328 in the "test tank" at the Willys plant. The driver is wearing a dive suit without the helmet.
The test tank was actually just a low road within the plant that was dammed up to hold water.
Thanks to Bill Norris for the photo.

The CJV-35/U Underwater Ventilation System is very similar to the M-38 system. Some of this information is taken from the M-38 Ventilation System Article since many of the components are the same.

2. Drivetrain

3. Carburetor venting

4. Distributor venting

5. Windshield wiper venting

6. Fuel tank venting

7. Master cylinder venting

Ventilation of internal combustion engines is necessary to prevent harmful condensation, to relieve internal pressures set up by the action of rapidly moving hot parts, and to rid the crankcase section of volatile vapors. When the CJV-35/U was built, engines usually were vented directly to the atmosphere through suitable openings or vents. The CJV-35/U engine was a standard 4 cylinder jeep engine with the added components to make it waterproof, or watertight, which also makes it airtight. Therefore, the method used to ventilate the engine is different than most engines of the time period. It has the same system utilized by most modern automobiles, the PCV (positive crankcase ventilation) system. A PCV system is a closed system within the normal engine intake air and exhaust systems. During normal operation with the engine running, the vacuum created in the engine intake manifold draws fresh air into the ventilating system through the upper crankcase vent control valve on the air intake crossover pipe assembly. The flow of air enters the oil filler pipe. The air then passes downward into the crankcase. The contaminated crankcase air leaves the cylinder block at the side valve cover through the series of parts that include the lower crankcase vent control valve and the metering valve (PCV valve). The air is then drawn into the engine intake manifold and continues on into the cylinders, where it is burned, and then exhausted into the engine exhaust system. During normal operation the two vent control valves are open and play no part in the ventilating system. The metering valve (PCV valve) however, operates to automatically control the amount of vacuum developed within the engine crankcase regardless of the engine speed. Prior to entering deep water, the vehicle operator closes the two vent control valves by pulling out the fording control cable on the dash. Closing the vent valves renders the entire engine ventilating system inoperative. This does not include the vent systems of the carburetor, wipers, master cylinder, fuel tank and the distributor, which are vented independently. When the vent control valves are closed, with the engine running, the unrelieved pressure within the engine builds up to approximately 2-psi. Internal engine pressure will rarely go higher than 2-psi. At higher pressure, leakage occurs through the crankshaft front and rear oil seals. This internal pressure offsets the external pressure of the water surrounding the engine and effectively prevents the entry of water into the engine past imperfectly sealed joints or through the front or rear oil seals.

The gear boxes would normally be vented to the atmosphere to eliminate internal pressure or vacuum from forming as they heat and cool with use. On the CJV-35/U the transmission and transfer case are internally connected by passageways and vent to the air filter. The transfer case has a tube that extends to the air filter by way of the right dash tee fitting on the passenger side of the firewall. The axle housings do not have a connection to the underwater venting system. This seems odd since they are similar to the other gearboxes. Axle breathers are located on both differential covers. A few illustrations, from the service manuals, show vent tubes from the rear axle and transfer case going inside the right frame rail. These vent tubes do not actually exist on the V-35 nor are there any parts listed for them.

3. Carburetor venting

The upper section of the carburetor must be open to atmospheric pressure to maintain a balanced condition in the carburetor. Therefore, the carburetor is vented by means of the vent tube that connects the top of the carburetor to the air intake pipe.

The distributor needs to have a supply of fresh air to eliminate moisture due to condensation and to remove oxides, which develop in all equipment where an electric spark is formed. The front edge of the distributor cap is connected to the air crossover pipe by a metal tube. This tube supplies clean air to the distributor. The lowest point of the distributor is connected by a metal tube to a special elbow fitting in the vacuum wiper supply Tee. The special elbow has a .043" restriction to limit the amount of vacuum in the distributor to a predetermined value.  It should be noted that since the wiper supply line is directly connected to the intake manifold it creates a vacuum leak to the carburetor.  The .043 restriction controls the vacuum leak and keeps the engine idle quality acceptable. Later in M-38 production, the restriction was made smaller, to .040”.

The vacuum supply to operate the windshield wiper comes from the intake manifold. To insure a constant vacuum regardless of engine speed the vacuum booster section of the fuel pump is connected in series between the intake manifold and the wiper supply tee fitting. Since the vehicle can be submerged, the wiper needs to have a fresh air source to avoid ingestion of water. This fresh air comes through the tube on the right side of the windshield frame which is connected to the air filter housing.

6. Fuel tank vent

The fuel tank is vented by a tube that runs from the top of the fuel tank to the left dash tee fitting on the driver's side of the firewall. Another tube crosses the firewall to the right dash tee; from there, a tube continues to the air cleaner. Although other tubes in the ventilation system are steel the fuel tank vent tube, from the tank to the left dash tee, is special thick walled copper tubing.

The brake master cylinder is vented through a tube that extends up between the foot pedals to the left dash tee, mounted on the driver's side of the firewall. Since the fuel tank vent is also connected to the left dash tee it is possible that gasoline could contaminate the brake system. With a full tank of fuel expansion could force gasoline up the vent tube to the left dash tee where it would drain into the master cylinder. This potential problem was eliminated in the next generation of underwater ventilation systems. The M-38 fuel tank vent ran directly to the air filter housing.

Parts

Using the Parts Catalog and an existing vehicle I attempted to locate every part associated with the ventilation system. Click on the images for a larger view with descriptions and part numbers. A database of all ventilation system components is found below the images.

   Distributor, engine ventilation, right side of engine

   Vacuum tubes, engine ventilator, left side of engine

     Carburetor vent, engine ventilator, left side of engine

    Intake and exhaust snorkels

    Dash tees and tubes, firewall right side (passenger), air filter removed

     Master cylinder

   Air filter connections, rear view

Special thanks to Harold West for all his help in writing this article. He has spent countless hours researching the CJV-35/U and has been incredibly generous with his time and efforts.

More information and comments are welcome,
Bob W.
Click here for contact information