R21EC Raw Cooling Water

[bymiller]

Just returned from an extensive "shake down" trip (working on a report) and noticed that some mornings it seemed to take a long time (several minutes) before cooling water was visible at the exhaust. I checked the raw water strainer every evening and removed and cleaned it almost every day. Mine has the very fine screen. Is it possible that removing the strainer causes the pump to lose prime?

The last day of the trip it took at least 5-10 minutes of running at idle and slow speed before water appeared. There was no gurgle, the exhaust sounded completely dry. The pump housing was very warm to the touch. The exhaust was getting quite steamy looking before water finally appeared. Once water appears the flow seems normal the rest of the day even with many stops and starts. I never had a temp alarm the whole trip.

Is there a thermostat that has to be satisfied at start up before water flows?

When I remove the strainer water flows into the bilge unless I shut off the thru-hull which I usually do when cleaning the strainer.

What do I need to check?

By

 

[Texas_Steve]

That sounds like a long time for exhaust water. I would check the impeller located under the round brass cap on the front of the engine to be sure all the fins are intact. Enjoy your boat. Great economical head turner!

 

[Capt’nKarl]

You should see water coming out of the exhaust port within 10 seconds of starting the engine. I would check the raw water impeller to make sure all the blades are intact.
Karl

 

[bymiller]

Impeller is good and I get what seems to be good flow once the flow starts.

 

[SlackwaterJack]

Assuming the boat is in the water...
check the inlet for obstruction...also, wouldn't be the first time I've seen the inside layers of a suction hose partially collapsed either. You could have an air leak that's effecting suction, is the little water-strainer's gasket missing? or the seal for the coolant-flush fitting?
Until engine operating temp is reached the Thermostat doesn't circulate much to the exchanger but some bypasses the thermostat and exchanger and goes right to the mixing elbow...that hose or it's mixing elbow connection may be obstructed.
because the pump housing gets very hot but the impeller isn't damaged I would check the pressure side (pump to elbow) first

 

[knotflying]

The thermostat is in the closed cooling system and should not have anything to do with raw water cooling. It sounds like you are getting poor water flow. My thoughts are there may be a blockage after the impeller. If it were before the impeller I would think with such low water flow the impeller would burn up. I am also surprised that your engine temperature is staying cool with such poor flow. I would check for a blockage after the pump.

 

[SlackwaterJack]

his inquiry is about lack of exhaust cooling water(raw) not about engine overheating

 

[bymiller]

Thanks for all of the comments. I also received several private messages and here is what I now think is happening.

The belt is tight.

After working some more on it this afternoon I think it may be caused by my cleaning the strainer. Here's what I did. I have a bucket with a hose that I attached to the hose port in the raw water line just past the strainer. The engine had not been started for several days and water came out the exhaust almost immediately. A while later I opened the strainer, put it back together and reconnected the bucket and hose. The hose is clear and there was quite a large air bubble in it. I started the engine to see how long it would take for the pump to clear the bubble and start pumping water. It appears that the pump does not have real strong suction as it took maybe 10 or 15 seconds for the air to get out of the hose. Same symptom I was seeing on the initial start each morning.

Al Coombs, from whom I purchased the boat, suggested opening the garden hose fitting in the raw water line to fill the strainer. Because the strainer and fitting are below the water line this would eliminate the air in the line from having the strainer off.

Next time I take it out I plan to run through the scenario of opening the hose fitting to remove air from the supply line.

The impeller is good, the o-ring on the housing is good, the cover screws are tight, and the belt is tight. The weird thing is that as soon as I start seeing water in the exhaust, no matter how long it takes on the initial start, the cooling system worked perfectly the rest of the day. There were many starts in a typical day because of the numerous locks and water would be in the exhaust each time as soon as I started the engine. I really think removing the strainer is what caused the delay.

Thanks for your thoughts.

 

[abcandjrc]

......
Al Coombe, from whom I purchased the boat, suggested opening the garden hose fitting in the raw water line to fill the strainer. Because the strainer and fitting are below the water line this would eliminate the air in the line from having the strainer off........

I am not certain the strainer is below the water line but suspect it is since the cockpit sole is. At any rate, getting that trapped air out of the system should do the trick. Some would still be in the line between the water line and the inlet of the raw water pump, but it would be minimal and should draw into the pump more quickly.

I mentioned to By in an e-mail that I also would generally throttle the engine up to about 1000 rpm on a new start when launched off the trailer if the seacock had been open. For instance if I drained the system because cold weather was a possibility. That would be similar to the situation when the strainer has been opened for cleaning. I suspect that pulls any air-bubble into the raw water pump a lot faster.

To do that, just hold the shifter interlock button in on the shifter/throttle control. That prevents the gear change and gives independent control over the throttle. One shouldn't throttle up too far for that, since the engine and engine oil are cold at that point. Just a bit above the normal idle speed to encourage the flow. Once the exhaust is burping normally, throttle back to the "neutral" point in the shifter and the shifter will re-engage.

 

[bymiller]

AHA! I found it! Went out on the boat today it had last been run three days ago. When I started there was no water coming out the exhaust. Let it idle about 5 minutes and still no water. Increased the idle to 1,500 rpm for several minutes and occasionally a couple of drops would come out but no gurgling sound.

Since the ramp was not busy I decided to pull the discharge hose at the raw water pump. Started the engine and immediately had a good flow from the pump. Put my finger over it and the pressure seemed good. Next I took the raw water hose off of the elbow at the exhaust manifold. Again there was good flow and the water was very warm. Pulled the 90 degree elbow from the exhaust pipe and could see it had some carbon. I could blow through it but I didn't see light. Cleaned it out with my screwdriver and could now see light. Next I stuck the screwdriver into the hole in the exhaust pipe and could feel "stuff". Moved the screwdriver around to free up the stuff. Put everything back together, started the engine and immediately had a good flow out the exhaust pipe!

My thinking is that when the pipe was completely cold, like first thing in the morning, the carbon was hard and clogged the water flow. Once the engine was started and the exhaust got hot it loosened up the deposits and allowed water to flow. It would stay warm enough all day, even with starting and stopping the engine, to continue to allow water to flow. Some days it was clogged in the morning and some days it was not. It never clogged during the day once the flow had started. I never had a high temp alarm.

Now I need to pull off the exhaust hose so I can look into the 180 degree elbow and see what I can see. I'm hoping that the only significant deposit will be right where the 90 degree fitting screws into the pipe. At any rate I feel confident the mystery is solved.

I also need to check the impeller. Hopefully it is not damaged. It was never really run dry. There was always water in the pump it just wasn't getting out of the pump. The housing would get warm but the impeller was still being cooled and lubricated by the water.

Thanks everyone for your thoughts on this.

I am once again a very happy boater!

 

[abcandjrc]

Good diagnostic work. I hadn't even considered that as part of the water-flow problem in my earlier posts.

I wonder if the trip through the canals added significant carbon deposits. I expect a lot of that was at fairly low throttle, wasn't it? Even in the Christmas boat parades I used to uncouple the throttle from the transmission and throttle up to 2000-2500 or so for a couple minutes every half hour or so to keep carbon deposits from forming in the head. That may have kept the exhaust elbow clear, too. I imagine that is a "cool spot" at low throttle settings and carbon might be inclined to build up.

 

[bymiller]

Most of my running this summer was done at 2,100 - 2,200 rpm for a speed of 7.0 mph. I admit I didn't often exceed that as I guess some recommend running full throttle for intervals. Spent very little time running less than 2,000. Some of the Canadian canals are speed limited at 10k which is about 2,000 for me.

Will know more after pulling the hose and checking inside of the elbow today.