Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 197Get this manual
Theory Of Operation The Power Trim system consists of an electric motor,
pressurized fluid reservoir, pump and trim cylinder
The remote control (or trim panel) is equipped with switch that is used for trimming the outboard "up" and "down", and for tilting the outboard for shallow water operation (at slow speed) or for "trailering"The outboard can be trimmed "up" or "down" while engine ;s under power or when engine is not running
Excessive engine trim angle will result in insufficient water supply to water pump causing water pump andor powerhead overheating damageMake sure that water level is above gear housing water intake holes whenever engine is runningOperating "Up" circuit will actuate the "UpMrelay (located under engine cowl) and close the electric motor circuitThe electric motor will drive the pumpthus forcing automatic transmission fluid through internal passageways into the up" side of the trim cylinderThe trim cylindertrim rod will position the engine at the desired trim angle within the 20 maximum trim range The power trim system is designed so the engine cannot be trimmed beyond the 20 maximum trim angle as long as engine RPM is above approximately 2000 RPM The engine can be raised beyond the 20 maximum trim angle for shallow water operationetc by keeping the engine RPM below 2000 RPM If engine RPM increases above 2000 RPM, the thrust created by the propeller (if deep enough in the water) will cause the trim system to automatically lower the engine back to the 20 maximum trim angleTRIMMING OUTBOARDDOWN" (" IN" )