Overfilling tilt/trim system?

Question

I have a 1990 Sprint Pro Bass 266 with a 1990 115 HP Mercury outboard. I recently replaced a broken trim motor, but one day after I installed the new one, it failed. When I took it off, I discovered that trim fluid had gotten into the electric motor, causing it to fail. I sent it back to the vendor (who is sending me a replacement). However, they told me that the fluid got into the motor because I overfilled the system. I told them the the Merc Service manual says that you should fill the system until fluid is visible at the threads of the fill reservoir. So, you CAN'T overfill it. Any excess would just run over the top. They told me that you have to fill the system with the motor trimmed DOWN.

Now that is completely contrary to what I see in the Mercury manual. In fact, there is a big warning sticker on the boat that says you shouldn't open the fill plug with the unit trimmed down.

Does that sound right to anyone?

Answer 1

It is true, you fill with the engine (out-drive) down. The reason, if you fill with the engine up you have extra oil in the Rams (Hydraulic Cylinders), then when you lower the out-drive that extra oil only has one place to go; into the Reservoir.

But, if you not know and the manual is not clear on this. It be easy to be confused.

It good they give you another pump.

How I do this is fill with it down, raise it and lower it back down and let air settle, then top up. I aways left it just below the threads (Not touching the hole). The pumps I used had a very small vent hole under the fill s***w. Make sure it clear of paint and leave the rubber seal up so it will vent (Not s***w down all the way). It should not leak.

I would write/call the manufacture about the manual and clarify what it should say, it could have a misprint and need corrected.

Answer 2

The basic model has a high and a low mark on the side.  With the trim down the level should not drop below the low mark.  This could suck air into the system.  With the trim up the level should not go above the full mark.  If you overfill the unit most of the time it just makes a mess.  The fluid should not get in the motor if overfilled.  For fluid to get in the motor there would have to been a faulty seal or o-ring.  That is the basic model that I have worked with.  It is important when installing the motor/unit that when you fill it you know where it is trimmed at.  That way you know how much fluid to put in.  Run the trim a couple times and fill if needed.  Good luck