Catalina U12 not flowing water through Motor

[2xcrash]

Posted this in the wrong place, maybe I can get some advice here.


All right here we go. My 82 Catalina 30 has been slowly loosing flow off the back side exhaust over the last few months of use. After a couple months of sitting due to an charging problem. I got that fixed and it seemed that my thru hull cooling water inlet valve froze closed. I was able to tap it open and noticed that my inlet line and the outlet line from my thermostat had some scale. Cleared my inlet line my line from the thermostat that goes back to the fresh water inlet,also the line that goes from the thermostat to the exhaust.
they had scale but not what I would think would cause blockage.

More info. Its a fresh water system. No filter. I had checked the pump impellers a few weeks ago to see if it needed changing and it looked good. No missing veins.

So here is what Im dealing with

I have water to the inlet of the pump, and Id say it flows about a gallon in 3 min.

When I take the outlet to the pump hose off, water will spurt out pretty good. cant say how much but it was enough to move the towel that I used to keep from getting water all over the place.

Now I worried I have plugged in the block because I have taken the thermostat off to see if it was clear,it was, and if I was getting flow back there and I'm not getting anything.

Can my water pump be putting enough water out to make me think it's working and its getting backed off by the exhaust?

the exhaust and where the water meets the exhaust is clear of any scale. The inlet to the muffler is clear. I didn't check the outlet of the exhaust but I also ran the motor without the water line connected to the exhaust and nothing came out. Also my muffler was dry. I figures it should have something in it but nothing.

Thanks in advance. Still new to sailboats and their motors learning as I go ...

[Compass790]

When you say you have no filter do you mean the sea water is not filtered? It could be a plugged up heat exchanger .I'm not too good at verbal descriptions so I might not understand your problem correctly.
It may help if you post the make & model of your engine & then the CF users that have that engine would be better equipped to help

[2xcrash]

It’s a universal diesel 12. It doesn’t have a heat exchanger.
I rebuilt the water pump and if I start the motor with the discharge disconnected it’s shooting water pretty good.
Now today I disconnected the water line that leaves the motor and try to blow through the engine block it’s blocked solid.

[Compass790]

Ok, unless broken off impeller vanes are blocking your cooling galleries somewhere you probably need to descale the block. But try blowing thru the block with a garden hose first. Try in both directions
Use the google custom search to look up descaling or look on youtube. Plenty of info available