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Trekka · 02-12-2018, 19:40

Need help on a procedure to deal with a raw water cooling issue.

Have a Perkins 4-108 that was not run for 3 years.

Before starting I drained lube oil, added new oil and filter. Drained about 20gals of old diesel fuel, added 24gal new and new filter. Coolant drained when heat exchanger removed and cleaned. New coolant added. Seacocks, including raw water intake were disassembled, cleaned, lubed. Strainer checked and rinsed. New impeller in Sherwood pump.

After typical bleeding issues the engine runs, now seemingly like normal. Except there is no water in the exhaust. And none seems to be reaching the sherwood. Have a SpeedSeal so am able to easily check.

So, the seacock is open. Boat in water. But water not being pulled up by Sherwood and entering system.

What are likely issues? Best way to troubleshoot?

On next visit I plan to disconnect hose that joins an elbow about 2ft before the Sherwood. I will add a hose that goes in 5 gal pail of water and see if that is sucked up. If so, the problem will be somewhere between seacock and that point. What likely? Anyone had similar issue ever?

TIA for any productive thoughts...

**Don C L** · 02-12-2018, 19:52

My buddy had the same issue with a Volvo MD7A... wasn't the engine though, the seacock handle was broken and though it looked open, it wasn't. There could be growth in the thru-hull also.

Uncle Bob · 02-12-2018, 19:53

Quote:

Originally Posted by Trekka

Need help on a procedure to deal with a raw water cooling issue.

Have a Perkins 4-108 that was not run for 3 years.

Before starting I drained lube oil, added new oil and filter. Drained about 20gals of old diesel fuel, added 24gal new and new filter. Coolant drained when heat exchanger removed and cleaned. New coolant added. Seacocks, including raw water intake were disassembled, cleaned, lubed. Strainer checked and rinsed. New impeller in Sherwood pump.

After typical bleeding issues the engine runs, now seemingly like normal. Except there is no water in the exhaust. And none seems to be reaching the sherwood. Have a SpeedSeal so am able to easily check.

So, the seacock is open. Boat in water. But water not being pulled up by Sherwood and entering system.

What are likely issues? Best way to troubleshoot?

On next visit I plan to disconnect hose that joins an elbow about 2ft before the Sherwood. I will add a hose that goes in 5 gal pail of water and see if that is sucked up. If so, the problem will be somewhere between seacock and that point. What likely? Anyone had similar issue ever?

TIA for any productive thoughts...

My 2c worth, air in the hose between inlet and pump, Prime pump so no air in the inlet side and see how it goes.

AndyEss · 02-12-2018, 19:59

Check if your raw water hoses got reversed at the pump at re-assembly. I found this to be the problem on my boat when I first purchased it - no raw water at exhaust, even after changing impellers, etc.
The pump won’t pump if the hoses are reversed. Mark which one is which.

**Wotname** · 02-12-2018, 21:22

Quote:

Originally Posted by Trekka

.........

So, the seacock is open. Boat in water. But water not being pulled up by Sherwood and entering system.

What are likely issues? Best way to troubleshoot?

On next visit I plan to disconnect hose that joins an elbow about 2ft before the Sherwood. I will add a hose that goes in 5 gal pail of water and see if that is sucked up. If so, the problem will be somewhere between seacock and that point. What likely? Anyone had similar issue ever?

TIA for any productive thoughts...

Presumably there is a raw water strainer in the raw water circuit - either inside the boat or outside (i.e. external to the seacock).

Should be easy to find out why raw water isn't making it's way to the Sherwood.

Pull the hose off the open seacock - water should flow into the boat.

If there is an strainer inside boat, is it above or below the water line?

If below, water should flow out of it when the top is removed?

If above, is the seal in good condition; if not the Sherwood will be sucking air, not water.

Is the Sherwood above or below the water line?

**a64pilot** · 03-12-2018, 06:55

I’d bet impeller. I have seen one that the brass inside spun in the rubber part meaning the paddles didn’t move.

However it ought to be easy to trouble shoot, removing the cover of the strainer with the seacock open should have water flowing freely as most I think are under the water line.
If you get a free flow of water there then I’d remove the pump output hose and temp fit a hose on it and crank the motor, if the pump pumps a lot of water like it should, then something is blocked in the motor, perhaps the exhaust elbow.
Reinstalling the pump output hose and disconnecting the hose at the elbow will determine if the blockage is the heat Ex or the exhaust elbow

kmacdonald · 03-12-2018, 08:02

If the raw water pump is not in good shape it won't self prime. It could be a worn cam and wear plate or end cover in addition to the impeller.

billknny · 03-12-2018, 08:03

If you have checked the hose arrangement, and are sure it is right, try two things:

Grease the impeller with a good dose of silicone grease.that will help it generate suction which is hard when it is dry, and protect the impeller while you are running it dry troubleshooting it.

If that doesn't do the trick, you can prime it by pouring water into the outlet of the pump. That will also help get it primed. If the water drains quickly back through the pump, you might have the wrong impeller.

Cheechako · 03-12-2018, 08:15

With a 4-108 I have had an air lock after having it apart. I removed the thermostat housing and filled it up with hot water. But that was the closed loop pressurized side not the raw water side.
Is the raw water pump below the water line? It must not be and you need to prime it somehow. Or is the strainer too high/above water line not allowing water into the pump? If so, try filling it.

t588143 · 03-12-2018, 09:29

A common cause is a leaking strainer gasket. Strainers are most often fitted above the water line. This means that if a gasket leaks air is drawn in preventing water to be drawn up in the filter.

MV Wanderlust · 03-12-2018, 10:05

As others have said, it could easily be an air pocket in the intake. I'd recommend starting simple to rule out a couple of things.

With the seacock "open," is the strainer filling with raw water? If not, the seacock may not actually be open or there could be a blockage in the through hull. This can be tested and possibly eliminated by hooking up a hose to the output side of a wet/dry vacuum and forcing air into the mouth of the strainer. You might have to cup your hand or something around the hose to seal off the strainer. Close the seacock, open the strainer, set up the vacuum and turn it on, then open the seacock. If you hear air bubbling against the hull, you have an open and clear pathway from the strainer to the outside of the hull. That'd be a good thing. If you remove the vacuum, water should flow into the strainer and fill it. Close the strainer.

If you got that far and have water to the strainer, the problem lives between the strainer and the raw water pump intake. That's where my vapor lock turned out to be after a hose change. Remove the hose from the raw water intake, stick a garden hose into the raw water hose, and fill it to the brim with plain water. This will prime the raw water intake hose. Put a little white grease around the flange of the raw water intake on the pump and reinstall the now-filled hose. The grease isn't necessary for the test; it just helps get the hose off the next time.

With an open circuit from the through hull to the strainer and the hose from the strainer to the pump already primed, you should have water flow out the exhaust. If you don't, start by inspecting the pump, since it's next in line.

John

Siberian Sea · 03-12-2018, 10:14

Sounds to me like a problem with the raw seawater pump. Perhaps as easy as replacing the impeller. If left ideal for extended periods of time the impellers can become brittle, crack and once the engine is started the impeller virtually falls apart to the point it pumps nothing. I would remove the hose going to the pump and see is water is getting there first and if so then close the sea cock and open the pump and inspect the impeller. If nothing is wrong there and impeller will rotate when engine runs then I would assume there must be an obstruction after the pump perhaps in the heat exchanger. I feel confident your going to find the problem very soon and in short order your engine will be up and ready to go

Sophia1 · 03-12-2018, 16:01

I have had similar issues with my impeller sticking after being installed.. You might try attaching a water hose to the hose leading into the raw water pump and then turn it on. That should get the impeller moving. Do not leave hose on for long.