Compressing air raises its temperature, which reduces change density and tends to defeat the purpose of supercharging. Sophisticated turbocharger installations include a heat exchanger, or aftercooler, between the compressor outlet and intake manifold. The cooling medium can be air, engine coolant, or—for marine applications—water. The plate and tube seawater-fed aftercooler used with the Yanmar 4LH-HTE boosts output to 135 hp, or 30 hp more than an identical engine without aftercooling.
Air-cooled heat exchangers work most efficiently when mounted in front of the radiator. Engine coolant should be taken off at the pump discharge and returned to some point low on the water jacket.
Air-cooled units require little attention, other than an occasional dust off. Liquid cooled heat exchangers should be cleaned as needed to remove scale and fouling, and periodically tested by blowing low-pressure (25-psi maximum) air through the tubes. Water intrusion into the intake tract can be expensive.