1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 320Get this manual
Troubleshooting Flow Diagram Outboard will not hold tilted position in reverse andor trails out during high speed decelerationInspect Manual Release ValveResult Result
Manual release valve andor O-ring damage
Manual release valve and O-rings appear to be OKReplace O-rings and proceedInspect Trim Rod Piston Check ValveResult Result