I noticed just prior to being ready to launch the boat for the season that the port outdrive would not stay up in its raised position.  Normally, the outdrive will stay in a raised position indefinitely.  So, I had to do some diagnostic work to figure out the cause of the problem.  I first checked for leaks, both outside and inside the boat and there was no sign of leakage.  This left the probable cause being blow-by within the trim cylinders or within the pump.

I needed to isolate the problem, hopefully, to either the cylinders or the pump.  I raised the outdrive and then tied the hydraulic lines together to see if the trim cylinders alone could hold up the outdrive.  Time will tell . . . I measured the extension of the trim cylinders and then monitored then over the course of 8 hours.  The outdrive did not lower.  So, this would indicate a problem with the pump.

I researched various pump rebuild approaches, but in the end decided to order a new trim pump and then rebuild the old pump to have as a spare.  Pictured below is the new pump.

I found an OEM equivalent pump online from one of my favorite part sources at a very good price versus a rebuild kit.  So, it made sense to get a new pump. (below left).  I removed the old pump and it looked like the mounting bracket need some attention due to an extensive amount of rust around the base. (below right)

I treated and painted the bracket, then installed the new pump and worked any air out of the lines.

Then it was a matter of testing the new pump to see that it could hold the outdrive in a raised position for an indefinite amount of time.

I set the outdrive to the trim limit and took a measurement of the trim cylinder extension (21-5/8”) .  I would look for this measurement not to change with the drive left overnight in that position.

The next morning I got the same measurement.  So, it looks like the outdrive trim issues was fixed.

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