Usage:
3406B Truck Engines (7FB35917-Up)
A new air-to-air aftercooler arrangement is now used in the 310 hp Family of 3406B Truck Engines (7FB35917Up). Formerly, a jacket water aftercooler was used.
The aftercooler is used to cool the inlet air after the air is compressed and heated by the turbocharger. With the former jacket water aftercooler, the amount of cooling is limited by the temperature of the coolant in cooling system. Currently, the coolant is approximately 90 °C (195°F).
The new air-to-air aftercooler uses ambient air to cool the compressed and heated inlet air. A separate air-to-air aftercooler core is mounted in front of the truck radiator core. Ambient air is drawn through both cores by the engine fan. The ambient air flowing through the aftercooler core, cools the inlet air. The new air-to-air aftercooler provides significantly lower average engine inlet air temperature over the entire operating range than the former jacket water aftercooler.
Some of the benefits of the cooler inlet air are better performance, increased fuel economy, anticipated reliability improvements and reduced emissions.
Illustration 1. Typical location of air aftercooler.
Illustration 2. Components of air-to-air aftercooler system.
The air-to-air aftercooler system is simple, reliable, effective and uses commercially available components. Most of the components in the system are provided by the OEM. Caterpillar provides the elbow at the turbocharger outlet. The OEM provides the tubing, aftercooler core, clamps and the elbow at the intake manifold. Therefore, the warranty of these parts is handled by the OEM.
The 310 hp Family of truck engines is the first rating to use the air-to-air aftercooler system. Other ratings such as 350 hp, 400 hp and 425 hp will also soon use air-to-air aftercooling.
When the engine arrangement is changed from jacket water aftercooling (JWAC) to air-to-air aftercooling (ATAAC), the following other changes are also made.
Maintenance
The maintenance of air-to-air aftercoolers is not difficult. Externally, debris or salt can be removed from the aftercooler core fins with a firm stainless wire brush and soapy water. Internally, the core can be cleaned with a solvent and flushed with hot soapy water followed with clean water. Caustic cleaners should not be used.
FT1984 lists the pieces necessary to plug the core for a pressure test to determine leakage. Attach an air supply line, air pressure regulator, relief valve, gauge and shutoff valve.
Pressurize the core to 207 kPa (30 psi) then close the shutoff valve. The air pressure trapped in the core should not decrease more than 34 kPa (5 psi) is 15 seconds.
The core can be checked for internal blockage by monitoring the pressure drop between the turbocharger outlet and the intake manifold. The pressure drop should not exceed 10 mm Hg (4 " Hg).
The air-to-air aftercooler was designed to provide 43°C (110 °F) intake manifold air temperature at rated power with 25° C (77°F) ram air at 48 kmph (30 mph).
Troubleshooting an engine equipped with ATAAC is similar to troubleshooting an engine with JWAC. When checking for low power or low inlet manifold pressure, you must check for air leaks in the core and air lines.
A complete audit procedure for the air-to-air system is included in Caterpillar Truck Engine Application and Installation Guide dated March 1985, Form No. LEGT5087.
When testing an air-to-air aftercooled engine in high ambient temperatures on a chassis dynamometer, there is a potential of adding a greater heat load to the jacket water cooling system. Therefore, jacket water temperatures should be monitored during the test.
The FT1438 Dynamometer Testing Aftercooler provides an air-to-water aftercooler to be used for engine dyno testing an air-to-air aftercooled engine. The instructions for this tool call for maintaining 65 °C (150°F) maximum inlet manifold temperature, but this is not correct for the 3406B Engine. The correct temperature is 43.3 °C (110°F).
Miscellaneous
Caterpillar discourages the use of winter front and shutters on air-to-air aftercooled engines. If a winter front must be used, a minimum of 20% of core surface must remain open to air flow under all operating conditions.
To maintain an adequate water pump cavitation temperature for efficient pump performance in an air-to-air aftercooled engine, Caterpillar recommends that the coolant mixture contain a minimum of 30% ethylene glycol, but no more than needed for the desired temperature protection. Dowtherm 209 Full-Fill Coolant cannot be substituted for ethylene glycol due to its inability to raise the water pump cavitation temperature.