Exhaust/Raw Water cooling troubleshooting

[Dan3121]

I have an O'Day 31 with a Universal M-18 diesel. While starting to motor out the other day, I realized there was almost no water coming from the exhaust. Immediately checked and replaced the impeller. Took the heat exchanger out and brought to a radiator shop to have it boiled out and pressure tested, as I could see some debris inside. Reinstalled the heat exchanger and still almost no water out of exhaust. Pulled the hose from the impeller to the heat exchanger and there is water flow. Disconnected the from the heat exchanger to the siphon break and cranked the engine, water was flowing. Checked the Mixing elbow; looks clear.

Anyone have any other thoughts?

When I loosened the exhaust flange, coolant came out. Not sure this is normal as I don't think coolant would normally be flowing through the flange. Anyone know for sure?

 

[Marmalade]

Sounds like you have checked a lot... I imagine you have tried most of these too, but I'll throw them out just in case.

1) close the seacock, pull the hose from it, and reopen... good water flow? (I once had a piece of seaweed get sucked in, and stuck right there in a 90-deg bend)

2) Reinstall hose to seacock, follow hose to the next connection... make sure these are no kinks! Next connection should be sea-strainer. (You have checked the strainer to make sure the basket isn't full of crap, right?)

3) With seacock closed, Remove inlet hose from strainer... open seacock and confirm good flow. Is your strainer above or below the waterline? If above, you'll have to drop the hose below the waterline.

4) Reinstall the inlet hose, follow the outlet hose from the strainer to the raw water-pump inlet. Make sure no kinks. Assuming your raw water pump is below the waterline, and assuming you have the strainer and hoses fully primed (if strainer is below waterline, this should basically be automatic)... you should get water flow here with the hose disconnected and the seacock open.

Question... when you replaced the impeller, did you make sure the strainer and hoses were fully primed? If not, and if your strainer is above the waterline, there's a chance you cooked the new impeller.

Did you install the impeller with the fins angled/deflected the right direction)? I've seen impellers break a fin or more because the stress in the fin "flipping" to the correct direction caused over stress/tear of the rubber... I ruined a new impeller this way once...

Good luck... keep us posted what you find!

 

[Dan3121]

Sounds like you have checked a lot... I imagine you have tried most of these too, but I'll throw them out just in case.

1) close the seacock, pull the hose from it, and reopen... good water flow? (I once had a piece of seaweed get sucked in, and stuck right there in a 90-deg bend)

2) Reinstall hose to seacock, follow hose to the next connection... make sure these are no kinks! Next connection should be sea-strainer. (You have checked the strainer to make sure the basket isn't full of crap, right?)

3) With seacock closed, Remove inlet hose from strainer... open seacock and confirm good flow. Is your strainer above or below the waterline? If above, you'll have to drop the hose below the waterline.

4) Reinstall the inlet hose, follow the outlet hose from the strainer to the raw water-pump inlet. Make sure no kinks. Assuming your raw water pump is below the waterline, and assuming you have the strainer and hoses fully primed (if strainer is below waterline, this should basically be automatic)... you should get water flow here with the hose disconnected and the seacock open.

Question... when you replaced the impeller, did you make sure the strainer and hoses were fully primed? If not, and if your strainer is above the waterline, there's a chance you cooked the new impeller.

Did you install the impeller with the fins angled/deflected the right direction)? I've seen impellers break a fin or more because the stress in the fin "flipping" to the correct direction caused over stress/tear of the rubber... I ruined a new impeller this way once...

Good luck... keep us posted what you find!

There is good flow to the impeller. There is no strainer on the boat yet. Good flow to and through the heat exchanger

 

[dmax]

If you have good flow into the mixing elbow it has to be something downstream from there, mixing elbow, muffler, exhaust hose. See if there's water in the muffler - if so, drain it out and see if it fills back up when the engine runs. The answer will tell you whether it's the elbow or the muffler exit/hose. The exhaust flange covers ports in the manifold which will leak coolant if exposed - you need to drain the manifold first.

 

[Dan3121]

If you have good flow into the mixing elbow it has to be something downstream from there, mixing elbow, muffler, exhaust hose. See if there's water in the muffler - if so, drain it out and see if it fills back up when the engine runs. The answer will tell you whether it's the elbow or the muffler exit/hose. The exhaust flange covers ports in the manifold which will leak coolant if exposed - you need to drain the manifold first.

Thanks for confirmation about the manifold. Muffler has water and refills

 

[Ward H]

As @dmax said, the exhaust flange closes off coolant channels in the manifold. You will need to ensure the engine coolant is at the proper level.
Since you had debris in the heat exchanger you could possibly have it down stream also.
How did you check the mixing elbow? On my M25XP it is about 3/8" ID. I find a piece of hose that you can push through it to ensure there isn't a pice clogging that.
Did you check for water coming out of the hose from the siphon break to mixing elbow?
Maybe try a different impeller? How is the cover plate? If corroded where it contacts the impeller try putting some fine grit sandpaper on a very flat surface and sanding the plate clean.
Also, did you replace the plate gasket or O-Ring? I had a failed O-ring which drove me nuts trying to find the cause of poor water flow.

 

[Johnb]

I have had scale block up the raw water exit on my exhaust manifold and cause problems. I found that just using lung power to blow through the various components you can diagnose whether it is the heat exchanger, exhaust manifold or mixing elbow.

After a comprehensive rebuild you can blow through them with almost no resistance