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Water flow

pugwash

Contributing Member
Well my boat is now out of the water and winterized. Now here is my dilemna:

Every spring so far I have trouble getting the raw water pump primed. Once it's primed, it is fine, but I have to pour copious amounts of water down the tube from the U-cooler into the water pump.
The reason is that the pump has to SUCK water through an 8' pipe to the v-drive cooler then back through another 8' hose back to the pump. When the hoses are empty, the pump can't pull water through.

My question: Why is it designed this way, why can't the pump just suck it from the through-hull fitting and pressure it through the v-drive cooler and back to the u-cooler? Is it maybe that the v-drive can only handle negative pressure?:confused:
 
I am guessing that something is inhibiting the normal operation of this pump. I probably have the exact same setup on my Silverton 34C and my routing from the pump is also the same. In the 12 times we have hauled and launched the boat over the years and in the 4 winter storages we have had, our pumps prime themselves near instantly. My next guess is that you have your intake seacocks operating smoothly... and that your hoses are not collapsed until they are filled with water ...possibly?
 
How does one check for collapsed hoses?

Once the pumps are primed, the flow out the exhaust is pretty healthy (I haven't actually measured it I must confess) although I do get some steam from both sides.

Co-incidentally, the riser temperatures on each engines vary by about 20 deg's. Strangely enough the port side of the Starboard engine and the starboard side of the port engine run around 150 degs and the outside are around 130-140, do you think it may be connected?

The boat is similar to your except it's the Silverton 34X.

The only other thing I might mention is that I completely drain all the hoses from the thru-hull to the water pump as I can't remove the drain plugs from the V-drive. I use a wet-dry vac.
 
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The collapsed hose is just a thought but I have read about delaminations in the layers and then either by suction or pressure the ID of the hose diameter gets reduced by the inherent collapse of the wall. As for your temperature dispcrepencies, it sure seems like a restriction of cooling water flow (steam). There are several things to rule out regardless. Like service intervals on your elbows (risers) Heat exchangers (assuming FWC) U-cooler blockage seawater strainer air leaks....The possibilties can mount up cumulatively.

We had an air leak ( a very small air leak) around the cap of a seawater strainer that introduced a small stream of bubbles into the water flow causing a rise in temperature at cruise of about 10 degrees. Another slight blockage in our exhaust elbows and together, they were causing temp problems. I will almost guarantee that to this day, I did not need to change the elbows despite the 4 yr mark in the time line. I really believe the air leak alone contributed to the majority of the problem. So, demonstrating the cumulative effect of little problems, I think you need to accurately gauge a few things first. Check the water flow with a bucket as described in the forum. What I thought LOOKED like a good deal of water, obviously was NOT. Sure looked it. Try cleaning the Heat exchangers, also as described here as well as the u-coolers and once YOU KNOW you have a flowing system, re-think the problem from another perspective.

Seems prudent anyhow..
 
I have a similar setup on my 350s... raw water cooled....and in the winter I drain the blocks and manifolds and then turn the engine on and run the "pink antifreeze" through the engine/V-drives until it comes out the exhaust pipes.......In the spring I flush the engines out with a garden hose attached to the sea cock and run the engines. In this manner I always have a "fluid" in all parts of the engines including the water pump........never had a probelm.
 
Thanks guys, you have given me food for thought. Incidentally, it is raw water cooled, but that doesn't make too much difference in regards to the suggestions.
I appreciate your help and will certainly look into it a bit further in spring...can't wait.
 
Typically the pump doesn't have very far to go to get water since most setups have the hoses laying below the water line. When the boat is sitting in the water, chances are there is water almost up to your pump. After she gets splashed in the spring, pull the intake hose off at the pump and slowly lower it into the bilge. That will tell you what level the water is at and how far your pump must go for it. Have seen many of these set ups with no priming issues. I also suspect there is a problem somewhere. When was the last time the pump was serviced?

To answer your question, the water goes through the v-drive first to keep it as cool as possible. It also minimizes the length of hose needed thereby shortening the cooling circuit; it would be more hose if done as you suggested. When running propperly, the set up works fine.
 
The pump was serviced the winter before last and checked again last spring when I had the problem again, the first time I assumed it was because I had serviced the pump and it needed priming for that reason.. The hoses as you say are below the waterline, however, the V-drive isn't, so I guess i'm just going to have to fill the hoses and v-drive before plunging the boat into the melted ice next spring.
 
If you have a sea water strainer(bronze type with the see thru cylinder) I'll bet you don't have a good seal at the top and it's sucking some air. That happened to me one spring and I replaced the rubber impeller, put it back on and still nothing. After some swearing I just wondered about the sea water strainer, put some blue rtv on the cork gasket and away it pumped.
 
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