Raw water intake blocked

[Paul Montgomery]

I have a Universal M3-20 diesel in my 1990 Catalina 30 which is running hot; I have checked out the usual suspects and I am pretty sure the problem is between my raw water filter and the through hull - when I open the shut off valve with the filter removed all I get is a trickle of water - I am thinking it should be gushing out. There is lot of weed at our marina at this time of year and my theory is that the intake into the boat has been partially blocked; I have tried to clear using a piece of wire but no luck.
Am I right in thinking the water should gush out with the thru hull valve open?
Is there some sort of cap on the hull that is preventing me from clearing the blockage out?
How do I clear the blockage?
Paul
Collingwood, ON

 

[Old Skool Neil]

The expected water flow with the filter removed and thru-hull valve open depends on the height of the filter. Near the waterline it won't flow much, above the waterline it won't flow at all, below the waterline flow should be good. The waterline on our boats is very near the fiberglass seat top of the dinette.

As an acid test, with the valve closed remove the hose from the thru-hull, then open the valve. You should have a frightening flow of water. If not, it's likely you have an external strainer that's clogged and prevents you from rodding it out from inside the boat. Time to go swimming or hire a diver.

It's for this exact reason that I removed my external strainer in favor of an internal raw water strainer and increased the thru-hull size from 1/2" to 3/4" at last haulout.

 

[Bob S]

Could you use the foot pump from a dinghy to try and blow it out from the inside? I don't have an external strainer. I did upgrade to a Perko strainer per Mainesail's recommendations. Much easier to clean grass from the inside.

 

[shipwreck66]

good suggestion. I just had mine out and noted how easy it would be to block up that external strainer. I even took a pic of it for people on here to reference since it keeps coming up as a topic. Luckily, where my slip is located doesn't have a lot of detrius in the water, but up near the marina restaurant and office there is so much algae and trash I'm amazed that the wealthy boatowners actually want those slips.

 

[Paul Montgomery]

thanks Neil-my boat does have an internal raw water strainer-I don't think there is any external screen-which is why I can't figure out why I can't just push whateever's clogging it out from the inside; time go for a swim and see what I can do from the outside.

 

[Bob S]

Paul,

I had a good sized barnacle at the entrance to the pump out thru hull. Maybe you have the same?

 

[Kings Gambit]

It's been a while so memory fades some of the detail here, but when my 11 hp Universal diesel on my 1980 P30 started running hot (totally raw-water cooled--no heat exhanger), I did the things that have been suggested and found that water flowed in at the sea cock with the hose off. The internal filter was also clear. When I detached the incoming hose from the engine block and back flushed, it was also clear. Looking in the other direction (direction of flow), I eventually found on the starboard side of the engine down low, a little cock valve in the piping. When I disconnected it for examination, a bit of rusted metal just big enough to block water flow into the engine itself through that valve fell out. After that was fixed, there was normal flow through the engine and it didn't over heat.

 

[shipwreck66]

Thanks KG, that's the engine I have and info that will probably keep me from chasing a dead end in the near future.

 

[Paul Montgomery]

it worked!

Bob - thanks for the suggestion to use the dinghy foot pump-worked perfectly-saved me a swim in some grungy water. Paul

 

[mortyd]

ok louis, who were the usual suspects? i changed my impeller without an exit visa and the problem either committed suicide or was shot trying to escape from the same problem you seem to have.

 

[Bob S]

Glad you had good results! Not too much fum swimming under in murky water.