Power trim not operating correctly

The power trim on my Mercruiser 888 does not operate correctly. When the rams are pushed in manually and everything properly bled, the hydraulic lines connected, and the UP button pushed, the rams go out normally. When the DOWN button is pushed, the rams return normally the first time. But on each successive try, the rams retract less and less until they are fully extended and will not return at all.

I had the pump rebuilt and the valve body checked by API Marine. The hydraulic rams are new by Sierra Marine. All bleeding procedures have been performed repeatedly, but the problem continues.

Any suggestions?

Use straight 20 weight oil if you are not already.

The old style pumps like heavier oil then the newer one.

I put 5w30 in. Is that too thin?

try straight 20w........5 w is too thin........