Trim pump or rams issue?

[Toddavid]

Last season I hit a submerged log at speed, ripped the outdrive off. No hull damage, so a brand new DPS-B outdrive, transom assembly, rams, etc. were installed by a VP authorized dealer/repair center.

About halfway through this season, I started to notice that despite trimming up when on plane, and the gauge accurately reflecting my inputs, I’d glance down after a while at speed and notice my gauge showed I was trimmed fully down. It’s happened a couple dozen times since then.

Along with the new drive assembly came a brand new trim sender, and the gauge was replaced a couple seasons ago, so I don’t think this is a false reading. The gauge doesn’t fluctuate, either, which tends to happen with a flaky sender.

No external oil leaks.

I store the boat on the hard, and left the drive 3/4 down and monitored it for a week, and it did not drop further.

Checking the dipstick on the drive, I see it is a bit overfilled, but the oil looks clean, no water fouling. I think this trim pump design uses the drive fluid for hydraulic action? Maybe the overfill is causing cavitation which causes loss of pressure underway?

Thanks.

 

[Bondo]

Ayuh,...... Look closer at the trim pump,.... it should have it's own oil supply, as it doesn't use drive oil,....
It's usually Atf, or hyd. oil, or motor oil,.....

 

[Horigan]

Even if the trim pump reservoir is full, you could still be leaking internally across the piston seals. Note that you need to trim the drive all the way up before you open the reservoir. At other positions the reservoir is pressurized.

 

[Toddavid]

Even if the trim pump reservoir is full, you could still be leaking internally across the piston seals. Note that you need to trim the drive all the way up before you open the reservoir. At other positions the reservoir is pressurized.

Are you sure it needs to be up? This post says the opposite:

https://forums.iboats.com/threads/checking-oil-for-trim-motor-volvo-penta.535610/post-3853403

And if fluid was leaking past the piston seals, shouldn’t that cause the drive to slowly drop on its own when partially trimmed down? It didn’t do that when I watched for a week, trimmed down 3/4.

 

[Horigan]

Good point. The SX-M manual says the opposite, and I assumed it was the same on later drives/trim pumps.

On the seal leakage, gravity puts a much lower load on the seals than drive thrust, so it still could be the seals.