2001 Santego Merc 8.1s Horizon raw water cooling

[2001santego]

Pro active maintenance performed for the new boating season. Replaced impellers and orings for raw water circuits on both engines. Brass pump housing was smooth and clean on the interior, I also used a generous amount of silicone paste lubricant on the impeller.



Start port engine and expect to see flow out my exhaust port within 15-20 seconds, after 30 seconds no water. Waited another 20 seconds and shut engine down. Verified 1.Raw Water Thru hull is open and flow is unobstructed
2. Strainer free and clear

Removed the raw water pump and verified no issues with plumbing of hoses and new impeller and oring. All was still good.
2nd attempt to start and same result.

Closed raw water seacock, removed hose and connected a city water supply, started engine and after 15-20 seconds I can hear the muffler downstream of the exhaust manifolds filling and see exhaust water flowing. At this point I am thinking somehow the circuit was air bound and the pump could not overcome a pocket of air.
Re attach hose to thru hull, open thru hull, start motor and once again, no raw water after 45 seconds.

Out of frusrtation and day light burning I attempt the starboard motor and to my dismay same problem, but when city water was fed through the 1st hose after the thru hull, the water flows through and exits the exhaust port.

I am really scratching my head here, has anyone experienced any thing like this. Any help is greatly appreciated.

[Viper]

Tony, did you try chopping the throttle a few times? Usually that's all it takes.

[tomschauer]

When starting from dry, I have to bring my mercs up to about 2000 rpms for a few seconds to pull the water up to the pump.
I've had to do this on every merc boat i have owned that has the engine mounted pump.
Alpha out drives have the pump below the water line, so no problem with them.

[2001santego]

Qr Bbpost Tony, did you try chopping the throttle a few times? Usually that's all it takes.

Yes, I revved from idle to 2000 then 2500 a couple times. I dug up my service manual and the flow diagram for raw water. On either side of each engine is the actuator that you would use to air pump any seawater in the circuit. I suspect it has a ball/ spring check assembly that’s stuck open or closed. I’m goiing to troubleshoot further today

[bud37]

Unless they were already bad the problem seems to have started with the impeller replacement......the only thing that sticks out to me from your explanation is the use of lots of silicone grease.....now that may be fine but generally liberal dish soap is the ticket and the soap suds let you know when success is achieved if the exhaust ports are hard to monitor. One side would be one thing but you have both sides the same, curious.......good luck man.....you may be onto something if that air fitting is something that was disturbed.

[Viper]

Qr Bbpost

Qr Bbpost Tony, did you try chopping the throttle a few times? Usually that's all it takes.

Yes, I revved from idle to 2000 then 2500 a couple times. I dug up my service manual and the flow diagram for raw water. On either side of each engine is the actuator that you would use to air pump any seawater in the circuit. I suspect it has a ball/ spring check assembly that’s stuck open or closed. I’m going to troubleshoot further today

Make sure you relieve the pressure by pulling the ring on the relief valve in case the system is still pressurized.

[buster53]

Ok, the same thing happened to a buddy this past weekend. Way different engine, but an impeller is an impeller. He forgot to put the key in. Without the key, the shaft just spins and won’t turn the impeller. Any chance you did the same?

[Cooler]

I had a similar experience at launch. The main reason was an air lock in the hose coming from raw water inlet. Loosened hose near t-stat housing and could hear the pressure hissing out. Now have good water flow, but t-stat needs replacing. Engine was running 20 degrees hotter than normal. ( 160 is normal ) My starboard engine ran 10 degrees cooler than normal, probably because of water temp in bay. Replacing both t-stats this week. er

[Viper]

Qr Bbpost Ok, the same thing happened to a buddy this past weekend. Way different engine, but an impeller is an impeller. He forgot to put the key in. Without the key, the shaft just spins and won’t turn the impeller. Any chance you did the same?

No key in a Merc

[2001santego]

Hey folks. Finally got some time to trouble shoot The new impellers are fine and working great. I have flow from output of raw water pump thru trans cooler thru oil cooler thru fuel cool and thru heat exchanger. I removed the 2 hoses on the manifold inlet and the top two outlets on the riser before it dumps into the exhaust elbow. Hooked up city water to inlet to flush and clear and prove flow and activate a ball check that moves either up or down when the raw water pump is running. Flow was good so reconnect all hoses and start engine and at idle rpm, after 15-20 seconds I hear the muffler filling and finally the exhaust has water flowing.

I’ve winterized this vessel myself the last 5 yrs but never broke the prime of winterizing fluid before launching in the spring

I’m thinking the ball checks got jammed into position when I removed the raw water pumps and the pump did not have enough power to unseat it and allow flow

BB3FD781-A69D-46C9-B521-CF792E1D3AFE.jpeg

I want to thank all you guys for taking the time to send feedback and info.

Wishing all boaters a great season. Cheers. Time for a beer