Water Inside Cowling of Mercury 250 ProXS

[Bass Cat Boats]

Where do this boat come from? Or have you owned it since new, and what reservoirs do you Fish? There is no deflection from Power Poles or Talons, we have multiple videos debunking that myth.

[oldtimer57]

Is your speedo working. If that connection pops loose, it is usually connected inside the rigging tube and at speed, that will dump a ton of water inside the cowl. If it is not coming in around the cowl, which seems impossible if the seal is in even close to reasonable condition (the powerhead is WAY above the surface of the water and usually only gets drops of water on it), then it has to either be a leak in the water lines under the cowl, or else the speedo. Since the dealer cant see it leak when running it out of the water, Id strongly suspect the speedo tube. At 70+ mph, the water pressure is around 70 PSI. This is not a linear curve, in that at 110mph or so, pressure is over 200 psi. 70PSI will dump a ton of water out that tube.

[louie3252]

Maybe your coming off plane too fast? water coming in the back some how? I had my compressor reed valve recall done at 30 hours, by a old mercury racing guy, and he said from looking at the reed valve/ water spots and light corrosion that I had been over trimming and the spray was getting stucked in there at WOT. Can you see water marks or corrosion on the block or some where on the engine? The thermostat code/ issue on the pro xs, IMO is kinda nature of the beast, its not the best of designs and needs to be monitored/ service checked often.

[oldtimer57]

If the gasket around the cowl is good, which the dealer said it was, then there is not much room for water to get in through chopping the throttle. Might wash over the rear deck, but wont flood the motor. Merc designs these things to prevent water intrusion as some saltwater users back up rapidly which will let waves wash over the back of the cowl.Something is wrong/broken, most likely speedo-related since the dealer saw nothing running on muffs. There are at least two junctions/connections. One where you remove the lower unit for service. One somewhere between the area inside the cowl and the rigging tube where the tube to the speedo is routed.

[Roostertail1964]

The boat was purchased new from Bass Cat in 2014. The speedo has NEVER worked.

[Bass Cat Boats]

That might explain the excessive water intrusion the service tech mentioned, then…It is easy to follow the black speedo tube. Comes up from the lower unit close to the shift shaft. Also other end should come from boat through rigging tube. It will be much smaller than the oil line, the fuel line, and the oil tank pressure line. You should have four tubes coming through the rigging tube. Also large + and – cables for motor, and then at least one other one (main wiring harness) as well as a possible CAN bus (blue) wire if you have anything like a mercmonitor or other smart instruments. Last two things are the shift and throttle cables which are obvious.

[Bass Cat Boats]

Alright, the water has a source… Again what reservoir?

[Roostertail1964]

Raystown Lake south central Pennsylvania most recently.

[jcdogfish]

I had a leak on the engine right below the flush out below the lower cowl. It never overheated or gave low water pressure but it put out enough water to fill the lower cowl. The water would go from the cowl, down the cable rigging tube and into the boat. I looked for leaking hoses and pumps for a couple of weeks. One day I picked up the rigging tube and heard the water dump in the boat. I looked at the engine running with the cowl off and never saw the leak. It was hidden behind the flush out hose and lower cowl. and the water skeeted down so unless you looked in with a light I never noticed it.

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