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2000 merc 125 Trim

J

Jhanratt

Regular Contributor
I need some advice with a trim pump problem on my 2000 mercury 125 outboard. It trims up and down without load perfectly on the trailer or in water. It also trims up under full load every time (against full throttle torque). Trim down under full load works fine and it holds against reverse just fine as well. The issue only occurs when I trim up and out just a bit too high under full load. After a certain point it will not trim back down. If I let off on throttle or turn the boat it will trim down and work perfectly again. It's trims just past optimum operating trim and then will not trim back down again.

How do I go about fixing this? I have had the boat since it was almost new and the Trim motor and pump are original. The boat is fairly high use-age. I have 1200 hours on this fish finder and I would guess the boat at 1500 hours total. It is primarily a fresh water boat but it does go to the salt for a week or two a year. It is very well maintained and is in excellent overall condition. I do all my own work including a complete re-seal and bearing of the leg a few years ago but I have never tied into a trim pump and I am looking for advice. I own the full manual and have reviewed the chapter on dis-assembly and rebuild but the troubleshooting section does not describe this particular symptom.

BTW about 5-7 years ago on the first trip out of the season the leg refused to move. The pump was running but it would not trim up or down. I "fixed it" by lifting up on the leg while my wife activated the switch. It moved immediately and has not malfunctioned again until this year.

Is there a complete rebuild kit I can buy for this?
Should I wait till winter and do a full tear down and rebuild?
Is this likely to degenerate over the summer and strand me?
I'm guessing I could use the bypass to set it and limp home?

Thank you all for your sage advice and wisdom.

Jeff
 
Last edited:
Update:

I drained the oil by opening the bypass and fill screws and removing them and refilled with new fluid. The oil that came out was dark red and by colour appeared to need changing but it was clean and water and corrosion free. I have not been able to water test it since the oil change so I don't know if it helped but I would doubt it based on the lack of any corrosion or water issues.
 
Update:

I water tested it yesterday and the problem remains unchanged. On trim up if I miss the peak of efficiency and it starts to cavitate or porpoise I cant trim it back down unless I back off throttle then it will trim down?

When I changed the oil I had the fill and bypass screws out and lifted the leg manually several times. No Hang ups at all.

Any advice???

Full rebuild over the winter???
 
Thank you I will try that but I'm pretty sure that's not it because it's smooth as silk when I lift the motor and lower it by hand. (With the oil fill and bypass screws removed). Also I regularly lube it in my maintenance so it has not been neglected.

I will try it for sure though!
 
So Tried lubing the pivot tubes and bleeding the oil and changing it several times.
Problem was solved over last winter with a new manifold and popet set. Also changes the seals on the ram.
In retrospect it might have been worth changing the entire trim pump set.
Regardless the manifold set, seals, and popets solved it.
Confirmed with several trouble free rides this spring.
 
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