Engine Service in Palm Beach

Insured & Factory Certified Technicians


The gear cooler (or transmission cooler) is a simple seawater cooled element responsible for cooling the transmission oil.  The transmission oil pump sends oil to the element where it passes over tubes with seawater flowing through them.  The heat from the transmission oil is transferred to the seawater and the oil continues its path back to the transmission.  The gear cooler is an often overlooked maintenance item because, being a part of the transmission, it isn’t always listed in the engine manufacturer’s maintenance plan.  The gear cooler element has relatively small diameter tubes.  These tubes are more likely to clog with growth and debris than that of the other components of the seawater system.  Between the smaller tubes and unintentional neglect, gear coolers often become very clogged.

The most common failure associated with the gear cooler is a rupture in the element which allows the oil to escape into the seawater system.  When this occurs, the transmission will pump itself dry very quickly.  As the oil runs out, the pressure drops, and the clutches inside the transmission begin to disengage.  If this occurs while the vessel is under a load, it is disastrous for the transmission.  As the clutches disengage with the drop in oil pressure, they are able to begin slipping.  This creates excessive friction and quickly destroys the clutch pack.  The vessel operator has almost no chance to catch the problem as it all happens too quickly.  By the time a problem is realized, the damage is done and the transmission will likely have to be removed from the boat and be rebuilt.

Many times a cooler that is close to failure can be caught during the cleaning process because the ultrasonic acid bath and subsequent pressure test can be enough to cause an already weak area to finally leak.


Gear cooler maintenance is usually just a matter of removing the cooler and having it ultrasonically cleaned at a radiator shop.

Gear Coolers