raw water blockage

[HalcyonS]

hi everyone,
I haven't been here for a while - all sorts of life complications.
So Today, I started the engine - having accidentally left the raw water intake open for a week - ran nicely with cooling water, then no cooling water. Took the water pump cover off - good impeller.
I've got a big bronze thru hull and valve, and as I recall - it been a while - a perforated plate over the intake. Nav le goes via about 4' of 1" hose to a big bronze strainer - ~ 10" x 4" original Wilcox Crittenden. So I'm guessing the blockage is in the thru-hull or in the line between valve and strainer.
How should I test? Thinking aloud here - I guess I'll disconnect the strainer to valve hose at the valve and drain back from strainer into bilge, and I can open valve to see flow from outside. If the blockage in in the thru-hull, I guess I need to dive, right?
That should isolate blockage location - unless the blockage is in the block, or the v-drive. Does this happen? How would I diagnose/cure?
Any suggestions much appreciated.

[JOHN COOKSON]

You could try disconnecting a cooling system hose somewhere at the midpoint of the water flow inlet -> to final outlet them start at that point and work back to the inlet or forward to the outlet until you find the blockage. The alternative is to start at one end of the cooling system and work from that end to the other end until you find the problem.
Manifolds have a nasty habit of becoming blocked.
This would be a good time to plumb for the Thatch Modification if you don't have it already.
You're RWC I presume?

ex TRUE GRIT

[Peter]

I was warming up my engine one day when the exhaust stopped spitting water. Took the cap off my winterizing tee and no water with thruhull open so must be plugged thruhull. Removed hose from winterizing tee and tried to blow it clear. No luck.

Thought about going to get an air compressor to blow it out but then it occurred to me to try connecting the bilge pump outlet to the hose and pumping water back through it. Had to dump a few pails of water in the bilge but it did the trick. A large jelly fish came up once it cleared

No diving required

Hope that helps

Peter

[Dave Neptune]

I was motoring across the Catalina Channel one winters day with my dog. About half way across the engine temp began to spike, no water! I spent the next hour or so trying to get the offending obstruction out of the intake without diving. When I finally decided I needed to dive I sat down below looking at the engine and took a shot in preparation for the dive. Well I got another idea and with some duct-tape and a fire extinguisher I managed to blow it out. However the extinguisher popped loose on the second "ga-dush" and blew water and powder all over the cabin. Popped the hose back on and was underway. I had a bit of a mess but was running cool. As I was cleaning up I noticed an outline of me that was clean against the starboard bunk and overhead.

Dave Neptune

[edwardc]

Another old trick: If you have an open thru-hull (not one with a slotted cover), you can ream it open from the inside with a small piece of rebar.

[Al Schober]

I've never been a fan of external strainers on the water inlet. I've had blockages in the past, and been able to clear them by removing the inlet hose and pushing a piece of dowel down through the ball valve and the hull fitting. Close the ball valve while you reconnect the hose, then you're good to go.

[romantic comedy]

I ran the engine using the washdown hose as a source of seawater just to see if it would work. it did.

Can also us the washdown hose to shoot thru the thru hull and try to clear the obstruction.

I also have a dowel to be used as a ram rod thru the hose from the thru hull.

have not had to do it yet. But then again, I put on my rain gear when it is sunny so it wont rain.

[HalcyonS]

Another old trick: If you have an open thru-hull (not one with a slotted cover), you can ream it open from the inside with a small piece of rebar.

yeah but - boat is in the water ....

[HalcyonS]

thanks everyone for helpful suggestions, I'm going to have a go at it today. Will report back.

[JOHN COOKSON]

Maybe Not

yeah but - boat is in the water ....

Leave the hose on the through hull fitting after removing it from the water pump. Support the hose in an upright manner (I taped it to a bulkhead) so the open end is above the waterline. Open the through hull ball valve, use a piece of rebar and ream through the ball valve.
Might not work on your boat because of access restrictions.

ex TRUE GRIT

[HalcyonS]

dodged a bullet?

I traced the raw water line to the engine, all sorts of skinning knuckles pulling hoses in the bilge - blockage was in the engine. I took the line off the manifold. Oddly, the first gallon or two of water was white like skim milk. But not the kind of oily white of an oil/water emulsion. (I think). I ran the engine for 15 minutes, all good, but I did not think to check the oil
Still its had salt water running through it for 50 years, one of these days its going to rust through. Any comments gratefully received.

[JOHN COOKSON]

Was the white milky stuff mineral deposits from with in the engine?
How often do you do an acid flush?

ex TRUE GRIT

[edwardc]

yeah but - boat is in the water ....

Exactly. if the boat was out, it would be easy to access the thru hull from outside.

With the valve closed, you remove the hose. If opening the valve does not produce water, you ream out the barnacles with a short piece of rebar and a small hammer if needed. The actual amount of water that comes in between removing the rebar and closing the valve, although scary, is quite small.

Of course, when dealing with thru-hulls, the prudent mechanic would have functioning pump(s) and a wood plug at the ready!

[HalcyonS]

Was the white milky stuff mineral deposits from with in the engine?
How often do you do an acid flush?

ex TRUE GRIT

err, a what? Seriously though, with 50 years of salt water running through it I don't want to do anything that might compromise the remaining iron

yes, I think it was 'mineral deposits' and it was certainly doom within the engine. It came out superfine not like scale in a teapot, so it seems like a fine white powdery buildup that didn't calcify/harden into lump.

Any idea what it would be? Oxide drop out from interacting metals?

[HalcyonS]

Of course, when dealing with thru-hulls, the prudent mechanic would have functioning pump(s) and a wood plug at the ready!

anyone who messes with thru hulls while in the water without an excess of precaution and care is asking for a very unwelcome surprise.