Help w/ Power Trim issue on Mercury Outboard

Hello all,

I have 1998 255CC Sea Pro w/ twin outboards.
Engines are 2004 MERCURY Carbureted Saltwater 200 HP CXL SW.

One of the outboards (Serial No. 0T816342, if you need more information) was leaking trim fluid from the power trim pistons, so w/ the help of a friend I bought a repair kit, took it down from the boat and replaced all the o-rings, screws, etc.
We put it back together and for the last 2-3 days (!) I have been in the process of adding the fluid/bleeding the air out and making sure it works as it should.

I have tried several procedures:

1. Trim it all the way up
2. Remove the plastic screw and add fluid till it starts to go out.
3. Do not close the fluid opening and trim down/up for up to 30 mins-40mins in order to get rid of the trapped air
=> Didn't work


1. Trim it all the way up
2. Remove the plastic screw and add fluid till it starts to go out.
3. Close the fluid opening and trim down and up.
4. Remove screw to let air flow out every time it is on the up position.
5. Repeat for 30-40 mins !
=> Didn't work


1. Trim it all the way up
2. Remove the plastic screw and add fluid till it starts to go out.
3. Close the fluid opening and trim down.
4. Use the manual release on the side to let the air escape.
5. Trim up.
4. Remove screw to let air flow out.
5. Repeat for 30-40 mins !
=> Didn't work



I uploaded a video so you can see my problem. Please let me know what am I doing wrong. What is the correct procedure to fill the trim fluid/ bleed the air out?

Here is the link to the short video (made w/ my phone, sorry for quality issues):
Power Trim Issues on 2004 Mercury Outboard 200 HP - YouTube

Thanks!

Re: Help w/ Power Trim issue on Mercury Outboard

Gee,I recommend: Trim up. Fill it. replace plug. trim down and then up and let her set 3 min. Now fill and repeat down/up wait cycle.

Re: Help w/ Power Trim issue on Mercury Outboard

Thanks. I tried today for a good 1 hr+, leaving the outboard in the up position for way longer than 3 minutes. No luck so far. The pistons are still stuck out (they do not get in while trimming down and the outboard itself is not being held if I trim up.. it slowly goes down on by itself.

Re: Help w/ Power Trim issue on Mercury Outboard

it looks to me like two problems in trim cylinder(s).

A) Top cap inner seal isn't working. That's the one inside the aluminum cap that holds in oil pressure when fluid pushes down on piston.

B) Piston is jammed. Usually caused by worn or wallowed top cap that allows piston shaft to wobble. Even with a leaky top seal, the weight of engine should lower itself. Since engine did not appear to lower then trim piston might be jammed. I would expect one of the trims to keep retracting and I would identify the bad piston simply because it ends up being the only one still holding up engine. Try a bucket and run the system longer to see if a 1/4" gap develops one one of the trim rods.

it could also possible but unlikely that the fluid path is plugged. The video indicates a complete blockage. Hydraulics do not have separate trim and tilt circuits. All three rams work together during trim. When end of trim is reached the tilt takes over because it is the only piston left. It moves faster simply because all fluid is directed into it instead of across three cylinders. If it was a hydraulic blockage or valve then you would expect to see failure of tilt ram as well.

Re: Help w/ Power Trim issue on Mercury Outboard

@RRitt:

B) sounds very possible => The top cap shows damage from previous abuse. Maybe somebody used a hammer to unscrew it(?).
I have 2 other units laying around with some good parts on them, I'll see if I can swap the caps and will report back. The o-rings on the caps and pistons were replaced as part of this process, but I'll inspect them again.

Thanks for your help.