Cooling System Blockage?

[Cpt. Bronze]

Model 5411, new to me Catalina '27. I am an amateur sailor as well as mechanic, so I need some hand holding...

When I bought the boat the cooling system was operating fine, with water discharging out the back. After running full throttle for 20-30 min water ceased to flow through the system.

--Pulled the outlet hose from the water pump and confirmed a healthy flow when engine is running, so I know all is well from the sea water inlet to the block.
--Pulled the hose from the thermostat to the exhaust and got zero flow.
--Removed the thermostat entirely and got zero flow.

I therefore assume there is some kind of major blockage happening inside the engine itself. Is there any other explanation? Is it reasonable that a blockage would impede 100% of the water flow?

Assuming I'm correct, what is the best way to clear the obstruction? Can I some how "back flush" by pumping water into the top of the engine and draining at the bottom? I saw a video of a guy doing something similar using an electric drill pump.

Thanks in advance for your thoughts.

[Dave Neptune]

First welcome to the MMI forum. If you have a blockage a back flush may free it up for a while bit it is still there and will return again.

You stated that you had good flow to the pump so that can be eliminated. From the pump the water is pumped into the block via a "tee" fitting on the side of the block below the alternator. Remove the line from the tee and check for flow and or an obstruction there. At the "tee" the water either flows into the block or around the block to the thermostat housing, this is the bypass and there may be a valve for adjusting as most have removed the t-stat and adjust engine temp with the "bypass valve". From there into the manifold which is notorious for plugging on the exit fitting.

Checking the pump itself is a good idea as if it was run dry for a time the veins on the impeller may have broken off and they will often plug things down stream.

Also if you have a strainer on the cooling system be sure it is not plugged or leaking air which will drastically reduce flow.

Follow the lines from the pump and check at the fittings for blockage.

Dave Neptune

[joe_db]

First welcome to the MMI forum. If you have a blockage a back flush may free it up for a while bit it is still there and will return again.

You stated that you had good flow to the pump so that can be eliminated. From the pump the water is pumped into the block via a "tee" fitting on the side of the block below the alternator. Remove the line from the tee and check for flow and or an obstruction there. At the "tee" the water either flows into the block or around the block to the thermostat housing, this is the bypass and there may be a valve for adjusting as most have removed the t-stat and adjust engine temp with the "bypass valve". From there into the manifold which is notorious for plugging on the exit fitting.

Checking the pump itself is a good idea as if it was run dry for a time the veins on the impeller may have broken off and they will often plug things down stream.

Also if you have a strainer on the cooling system be sure it is not plugged or leaking air which will drastically reduce flow.

Follow the lines from the pump and check at the fittings for blockage.

Dave Neptune

The 5411 looks like this:


I don't think the cooling system is the same as an Atomic 4.

[Dave Neptune]

Oops, thought he was referring to a Catalina model number, not a Westerbeke diesel.

Sorry, out

Dave Neptune

[ndutton]

Most marine engines, gas or diesel, have cooling systems that function much like our Atomic 4. That is, restrict the coolant flow through the block when cold but at the same time bypass it to the exhaust hot pipe by way of a dual action thermostat. This system provides critical full flow to the exhaust at all times.

I recently converted a Yanmar 1GM from RWC to FWC and in the design phase the original bypass with dual action thermostat was obvious. You should check yours carefully to see if it is the same type of system. If it is, it suggests to me the blockage is right before or at the exhaust injection point.

[Cpt. Bronze]

I recently converted a Yanmar 1GM from RWC to FWC and in the design phase the original bypass with dual action thermostat was obvious. You should check yours carefully to see if it is the same type of system. If it is, it suggests to me the blockage is right before or at the exhaust injection point.

I pulled the thermostat and still no water flowing. I also disconnected the hose going to the exhaust and nothing is coming out. This suggests to me the blockage/issue is occurring in between the block intake and the thermostat.

[ndutton]

Without know the details of your engine's cooling system any further comments from me would be speculative guesswork = not helpful. Do you have an engine manual? Can you get one?