Why Pressure Test Your Outboard’s Gearcase

Simple maintenance isn’t always so simple when it comes to outboard motors, but pressure testing the lower unit is pretty straightforward.

Outboard lower unit pressure test

A gearcase pressure test is one of those jobs “even a kid can do”. Pressure testing the lower unit tells you whether any of the motor’s seals are leaking. A leaking seal in the lower unit allows oil to escape from the gearcase, which robs the gears of the cooling and lubrication they need, and increases wear to all the internal components. 

Outboard gearcase pressure testing

Leaking seals also allow water to enter the gearcase, which leads to corrosion and even more damage inside the lower unit. Discovering milky oil when you change the gearcase lube is a sure indication that a seal has failed and plenty of water has mixed in with the oil. Pressure testing an outboard’s lower unit allows you to catch a leaking seal early, before too much water enters the gearcase.

To pressure test the lower unit, simply drain the old gearcase lube, hook up a gearcase pressure tester and measure whether the gearcase is capable of maintaining stable pressure. If you pressure test the lower unit every time you change the gear lube (every 100 hours or once per year), you’ll kill two birds with one stone, so to speak.

Another Reason to Pressure Test an Outboard

Leaking seals might cause oil to spill out of the engine. Spilling even the smallest amount of oil into US waters — even by accident — is a federal offense that carries (as of this writing) a $10,000 fine. 

Pressure testing an outboard’s lower unit doesn’t take much time, and the diagnostic benefits it provides saves you a whole lot of trouble down the line. Whether your outboard is a Yamaha, a Mercury or another make, watch the videos provided above to see how to perform a simple lower unit pressure test. 


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