No raw water in exhaust - troubleshoot

[Elie]

The strainer need to be well sealed(air tight) or else no pumping will occur. To help a bit a problematic impeller, you may fill (from the strainer) the hose with water. Once the pump start pumping that water it will remove any airlock and thing will start to be nice.

[thunderhoof]

On my boat the raw water strainer is above the pump. I closed the raw water seacock, then filled the strainer body to the top, screwed on the filter top and opened the seacock. This primed the raw water pump and all is well.

[Trekka]

Thanks for all the great responses. Good information there.

My task has been slowed by call for work each afternoon yesterday thru another couple days in a city 60 miles away. But I will have a few hours this morning.

To clarify, and answer some questions:

Strainer is about at waterline. Lid off and seacock open (definitely) the raw water settles about a half inch below top of suction pipe. The boat is riding 2-3 inches higher than normal at present. I removed the lid today, cleaned it and put some marine lube grease where the gasket contacts as well as the threads.

Impeller is new, the designated proper for the Sherwood. It spins when engine running. And not when engine off. There is a speedseal cover which I removed to check that. There is a key for the notch in the spindle and impeller which I carefully place when itnstalling.

When installing the impellor I put a little white teflon lube on the sides and blade tips just in case I had any issues that would have the engine running without water flow.

Hoses are on very tight and it is difficult to remove them. Partly because of how tightly attached. Partly because of difficulty accessing from directions that facilitate the proper effort - and direction of those efforts. (it's a boat after all. Nothing is simple to get to). I believe my best luck will be right at the pump, and just coming off the strainer.

Heat exchanger was removed and cleaned a couple months ago.

Seems like problem will be one of two things. Either vapor lock (strainer seal?) or blockage on intake side of pump. Or, some blockage after the output has gone through HE and entered exhaust manifold. (Hmmm I could fairly easy d/c the connecting hose right where raw water -post pump- enters the HE)

In the morning the mechanic who helped me get the engine ready for running a few days ago will be stopping by. I'll see what he thinks. In the meantime I think I will try putting water down hose from the pump back to the strainer. But first I will try blowing down it.

Back at it after a little sleep.

[skipperpete]

Since you have an easy to remove coverplate on the raw water pump, undo it and rotate the engine manually. A previous reply mentioned the impeller hub slipping but there is also a chance that the tang drive on the other end of the pump shaft is slipping or damaged. This test will remove doubts and save time finding the real cause.

[skipperpete]

Oops , sorry Trekka , missed the bit where you already did what I suggested🤢

[Trekka]

Did not intend to let this much time pass before posting the resolution. But fix came late in a winter afternoon. Followed by a race to get at least out the winding path around shoals to the river before complete darkness. Then off for an involved and prolonged job before the next dawn.

The proffered solution seemed crazy to me but nothing else had done more than short term flow and that at high rpms. My pump has a SpeedSeal cover and I was advised to take it off and turn it over. But that would mean no O ring (only recessed on inside of cover) and I did not have gaskets to use. I took a dab of marine lube grease I use for seacocks, smeared on the pump edge, and screwed the cover on inside out.

Fired up the Perkins and - water flow! Not perfect, as I found when idling while undoing docklines. Had to keep rpms up. Idling more than briefly the flow would stop and I had to remove an anode from heat exchanger to let flow start. Otherwise the exhaust pressure was too strong. But once flowing at 1200rpm or better I could replace the anode and flow continued.

(Once on the river I was very happy with performance of the added 2 inches of pitch on my prop and the clean hull.)

I thought this solution would be a surprise to everybody. But reading this thread again I see that the cover being worn was mentioned as a possibility. The inside clearly was worn, could both see and feel that. I wondered why this would be a problem so suddenly? Then I remembered...

Last couple seasons I was puzzled when, upon return to slip with engine temps good, I would go to idle as coasted in (floating dock!), dropped a spring, and stepped ashore to rig the remaining lines. Stern, bow, other bow, other stern, spring. Then step aboard to kill the engine - and it would be overheating! Not pegged yet but way higher than 190F) I wondered if the back and forth switching, with reversed prop flow was doing something to impede inflow? But the next time I’d go out the engine was fine. Until I returned and tied up.

I can see now the warning sign. The long very slow running coming back into marina past several docks to my inside dock. The idle time during final turns and maneuvers. Leaving engine idling until fully tied up. The low idle rpms were not delivering sufficient flow. When starting up of course I would look over the transom to verify flow. But that was not at slow idle rpms.

So the warning signs were there. I did not recognize them.

And unfortunately SpeadSeal is out of business. So no replacement cover available. But I can get a new G65 cover for about $155. I’ll keep the big SpeadSeal thumb screws and hope they can be used with a regular cover. At least then the removal for impeller swaps will be fairly quick.

Thanks to all of you for responding so quickly to my posted predicament. Hope this info will be of use to anyone researching this problem here in the future.

[a64pilot]

You can likely have the cover faced, or surfaced if you will, made smooth again at a machine shop.
Except for the apparent o-ring groove you could do it yourself.
Likely you could have one made for less than $155?

[kapnd]

Don’t know if you pulled off the supply hose, but there could be bits of previously destroyed impellers hiding between the pump and the strainer.
The rubber trash can move mysteriously up into the pumps intake screen, then disappear again when the engine is shut down, causing phantom overheats with no readily visible cause.