Can water in lower unit be so bad it impedes performance?

spoolin01

Seaman
Joined
Jul 30, 2002
Messages
60
Can water in the lower unit cause the oil to emulsify so badly that it gums up the works?

After a few trouble-free trips, a new issue arose yesterday with the old '74 Sportcraft with Merc 165 and L6 250. The boat now can't get much past just on plane, 12-13 kts. At higher throttle settings, the engine noise becomes deeper and more throaty, but no increase in speed. Many times in the past that has meant the fuel filter needed replacing, and I had just switched to the forward tank which hadn't been run in a few trips, but that didn't change anything this time.

I recently installed a proper NOS carb, which has worked well over a handful of trips and been a great improvement over the original. I took off the spark arrester and sloshed a few cc of gas from the old filter into the throat while the boat was running in gear and with the throttle set past the stage of proper response, but all the extra gas did was cause the engine to stall briefly before resuming its poor performance. I don't know if that was a good test or not, it was the only thing I could think of as a check for fuel starvation.

Up until the point where the boat stops accelerating, I doesn't appear to have less power than normal, and the motor will rev high quickly when out of gear.

I checked dwell and it was middle of proper range, but I didn't have the means to verify timing. Idle and slight throttle sound and feel normal to me, and we trolled for many hours with no sign of issue aside from this power limit.

So I'm wondering if the water intrusion issue in the drive could be the problem. Last season the shift bushing broke on the original lower unit, and the shop said they couldn't get it out. I bought a used replacement that pressure tested OK, took the upper and new lower to the shop to have them assemble and pressure test the whole. They replaced some upper seal where the driveshaft fits in, appear to have packed a bunch of grease up there I later found out, said something about how worn things looked in the upper, and said it was good to go. I put new gear oil in and after one outing it was clear there was water intrusion. I rechecked the empty lower for vacuum/pressure (can't recall which I used, maybe both), and it held overnight.

Figuring whatever problem there was at the upper end wouldn't be easy or cheap to fix, I decided to manage the water intrusion just with frequent oil changes, every 3 or 4 trips.

When I went to change the oil before this last trip, it was different than the opaque creamy brown usual stuff, it was darker and separated into a low viscosity liquid and some very thick stuff. It came out of the drain hole like curdled milk. There appeared to be some water droplets in the pan, which had never been the case. There was also some oil dripping off the prop mouth, which I've never had before.

This kind of thing is outside my experience, I've never left an outboard or outdrive run with water in the gearbox. Could the emulsified oil be so thick it won't let the gearbox rev? Could the water have damaged the internals? There was no sign of metal shavings in the old oil, or anything I recognized as rust.

I'm considering an outdrive swap to either a used Alpha One, or a new SEI clone. That at least hopefully solves the water issue for good. Before taking another tack with the performance issue, like pulling the carb and opening it up, I thought I'd check whether it's possible the outdrive is the issue.
 
Last edited:

77GlastronMT

Petty Officer 2nd Class
Joined
Aug 17, 2013
Messages
100
I wouldn't think it would be the oil/water mix, but more like the internals are starting to rust and creating friction which will rob lots of power plus destroy the internals.
 
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