Air in Raw Water System?

[BozSail]

I started our Perkins 4-108 engine this spring, having installed a new water pump">raw water pump over the winter. The engine started within 10 seconds and ran well (as it always has). However, after running for about 20 to 30 seconds, no water was coming out the exhaust, so I shut it down. I hooked up a 5 gallon tank in the cockpit to the raw water intake hose so it would gravity feed water to the raw water pump. Still couldn't get water exciting the exhaust. I re-checked the impeller to make sure it was okay. Then I removed the heat exchanger and cleaned it and installed new zincs. The exhaust elbow is new and clear. Still no water exciting the exhaust. QUESTION: Could the system be airlocked, preventing proper raw water flow? I'm at a loss to diagnose the problem. HELP.

[Marc1]

A nasty trick the flexible impeller can play you is to detach from the driving bush. All looks good but the rubber comes off the grooved bush and therefore no pumping.
You can open the front of the pump and see if the impeller turns if you crank the engine (not starting it) and also if water comes out. Make sure the seacokc is open

[BozSail]

Thanks Marc. I did all that and still no raw water out the exhaust. Is it possible for the Vetus valve to have a blockage. My gut says maybe there's either an air block or a physical blockage of some sort, after the heat exchanger... still stumped.

[Sailmonkey]

Is your strainer above or below the waterline?

Does water readily flow into the boat with the seacock open?

Is the lid on your strainer a tight seal? Ie, not allowing the pump to pull air instead of water?

The impeller pimps won’t get “air locked” as they’re a semi-positive displacement pump.

Once you confirm that water is able to reach the pump you can start looking further downstream of the pump.

[a64pilot]

I’d be suspicious of that new exhaust elbow.
You sure the water exit point is clear?

Disconnect the hose and blow air through it. The water hose of course.
Or disconnect the water hose and start the engine.

[sailah]

Be careful about running a bucket of water up in cockpit as I assume it's above the engine.

When you shut the engine down it can siphon the water in the bucket and end up doing unpleasant things like hydrolock your engine.

I also use the bucket and when I am using it on the hard or end-of-season to run antifreeze thru engine, I suck the bucket dry with intake hose and hold the hose up while engine is still running. I let it gargle until I can hear the raw water pump starving for 10 seconds dry.

Then I shut the engine down.

2 years ago during winterization I messed up somehow and an entire hose full of antifreeze ended up in my sump and chocolate milk oil. My uncle was less lucky and ended up with 2 cylinders full of water and bent con rods.

[Squanderbucks]

Any “air lock” would have to be before the pump. Flexible impeller pumps pressurize the system and would push out any air.
Wear plate or face plate could be worn or not sealed.
Close thru hill, remove impeller, put face plate back on and attach water hose from dock and put water through the hoses and see if water out exhaust. If not then likely the riser is blocked.

[Qayaq]

Turn over the engine and check the impellor shaft is turning. If you removed the pump from the outer set of bolts which requires re-alignment when refitting you may have snapped either the drive ears on the pump shaft or the drive peg on the injection pump. Hope thats not it.....

[bobgatz]

I have a 34 catalina, same thing happened to me last year upon launch, The raw water impeller looked good, but I changed it to another used one, that didn't pump either, finally put a new one in I had as a spare and started to pump water, not sure what it is where the impellers look good but don't pump, maybe cover was leaking I don't know for sure but the new impeller was the trick. I always suck the water out of a bucket now before launch so when I'm lifted in, I know I can start and move to my slip.

[t588143]

This happens almost always when the pump is completely dry. If the impeller does not seat 100% around the entire circumference, which a new impeller never does, and the inside wall of the pump is not 100% smooth, it will not be able to pump out the air and create the vacuum required to draw the water in. Moisture in the pump is required for cooling but also for sealing. The solution that most of the time works is to take the impeller out and "lubricate" it liberally with something that has some consistency and is water soluble (do not use ordinary grease) like green soap.

[bil56]

the new impeller has to prowl the pump body.
mount the new impeller with silicone grease.
check the sea water filter cover ...

[Stu Jackson]

Make sure the inside face of the faceplate is smooth.

[BozSail]

Originally Posted by Stu Jackson

Make sure the inside face of the faceplate is smooth.

Well... problem has been solved. The solution is embarrassing, but I'm posting it in the hope that someone else may avoid my dumb mistake. When I installed the new raw water pump over the winter, I installed it in the position that seemed to be appropriate. The inlet and outlet fittings were at the top of the pump, as was the cam on the inside cylinder of the pump. It did not pump raw water properly in this position (hence my reason for the original post). So... I decided to try mounting the pump upside down so that the inlet and outlet fittings were on the bottom of the pump. I then started the engine and had a healthy flow of raw water coming out the exhaust. I let the engine run for 20 minutes to bring it up to operating temp. All is good. I'll certainly remember that if I ever have to replace the whole pump again. [emoji5]
Thank you to everyone who offered their suggestions. Sometimes, I guess I learn things the hard way.

[redneckrob]

Originally Posted by sailah

Be careful about running a bucket of water up in cockpit as I assume it's above the engine.

When you shut the engine down it can siphon the water in the bucket and end up doing unpleasant things like hydrolock your engine.

I also use the bucket and when I am using it on the hard or end-of-season to run antifreeze thru engine, I suck the bucket dry with intake hose and hold the hose up while engine is still running. I let it gargle until I can hear the raw water pump starving for 10 seconds dry.

Then I shut the engine down.

2 years ago during winterization I messed up somehow and an entire hose full of antifreeze ended up in my sump and chocolate milk oil. My uncle was less lucky and ended up with 2 cylinders full of water and bent con rods.

I'm at a loss for how you could hydrolock your engine or end up with antifreeze in your sump by simply pulling antifreeze in through the intake hose such that you feel the need to run it dry? How is it any different to pull antifreeze through the raw water intake hose than to pull raw water through the raw water intake hose? You never run the thing dry when you're just pulling raw water through in normal operation, right? Am I missing something here?

[sailah]

Originally Posted by redneckrob

I'm at a loss for how you could hydrolock your engine or end up with antifreeze in your sump by simply pulling antifreeze in through the intake hose such that you feel the need to run it dry? How is it any different to pull antifreeze through the raw water intake hose than to pull raw water through the raw water intake hose? You never run the thing dry when you're just pulling raw water through in normal operation, right? Am I missing something here?

I run with large intake hose up to cockpit. The year it happened to me I was pumping antifreeze thru during winterization. I shut down too early and it siphoned out the rest of bucket which then backs up through exhaust elbow and into any open valves, down into cylinder. Vs normal operation it needs to suck it up through the strainer.

At least that's how I *think* it happened. Because I was questioning myself if I did it right all winter since I know better. So in the spring I made a note to myself to pull dipstick and sure enough it was chocolate milk and smelled like antifreeze. Then I decided to be real careful and pull all glow plugs before cranking engine. Had a couple blast of antifreeze come flying out so it was sitting in at least 1 cylinder all winter.

I had to run 4-5 oil changes back to back to get it running clear oil again.

Same way it happens if you try to start the engine too much, the pump pumps water but it doesn't have combustion exhaust to expel it.

So that's why I always let pump run dry for 5-10 seconds after the last bit of antifreeze is in engine. I replace my impeller every year anyways. Running it dry is probably overkill but that's my system to know for sure I won't have any head pressure.

At end of season I finally dealt with my bad head gasket and there were no signs of cylinder wear so I assume it was fine.

My uncle was not so lucky and cranked him Yanmar over with water in cylinders, bent some con rods. Said he could hear water sloshing around when turning over by hand

Always take safe route before cranking a diesel is my plan.