Re: 1994 115HP merc trim issue - wont go down all the way
systems that go up but won't go back down are typically a broken manual release valve. It can also be a water leak through motor or top of cylinder that causes system to have too much fluid.
In case of water leak, your trim fluid will be milky. Eventually, the overfull condition will cause your reservoir or cylinder to split.
In the case of MRV you need to extract the old MRV and examine it.
MRV is the slotted plastic fitting in side of pump base. There is a hole in transom bracket to access it. Make sure to use a very large screwdriver blade (or an old 3/4" chisel ground into a flat blade screwdriver). Your system is likely to spew oil all over everything when you remove the MRV and then continue dripping as much as another pint. Shielding rags and buckets are handy. Try to relieve pressure by running system up, blocking into place, and bumping the switch back down onto the blocks. If it does not lower at all then let it sit for a few hours hoping to release some of the pressure.
Once removed look to see if the MRV has three orings. If it does have three healthy orings then the MRV is okay. If it only has two orings but three slots then examine the fluid in drain bucket for the missing oring or pieces. System will not run for long with debris floating around. once you account for all debris then put in new mrv ay or orings. If the MRV has a broken off tip then you need to do a complete system rebuild. The old tip needs to be removed without damaging the aluminum. I use a very long and skinny drillbit along with a jig to keep it centered followed by a very long and skinny screw-extractor. Once extracted, the pump assembly needs to be completely broken down, washed, polished, greased, and assembled. The pump is almost certain to fail if you miss a particle of debris or scratch any of the metal parts.
If it is not water intrusion or MRV then I do not know what it could be. My own personal approach to do complete rebuilds instead of trouble shooting. Electric motors, relays, switches, and fuses are worth fixing one problem at a time. Hydraulics aren't. Troubleshooting individual hydraulic problems is a waste of time. If you fix one problem at a time then you end up with a system that keeps needing repairs every year or two. It is better to rebuild it all from top to bottom at the first sign of trouble.
