Suzuki DF 40 Service Manual page 233

8-23 POWER TRIM AND TILT
THERMAL VALVE
The PTT system incorporates a thermal valve for protection of the internal components, should excessive
downward force be exerted on the lower unit with the motor in a tilted position, or (in the case of an impact in
reverse gear), the outboard clamp/swivel brackets and the boat transom.
Should the propeller strike an underwater object whilst in reverse gear, a build up of pressure will be induced
in the lower cylinder chamber, whereby the outboard mounting bracket and/or the boat transom may sustain
damage. To prevent this, the thermal valve will open to relieve the oil pressure, thereby softening the impact.
Internal PTT circuits are protected, as the thermal valve will open to reduce oil pressure (caused by either hot
climate or abnormally heavy usage).
Tilt rod
Piston
Thermal valve
Lower
cylinder
chamber