370 yanmar sea water issue on 400 MS

[Kickback]

Hello All
Well I changed the sea water hose from strainer to pump, I’m pretty sure water drained back out on engine when hose was off. Put new hose Cleaned sea strainer out opened sea cock allowed to fill and run over then capped it. Let set for a while, Rolled engine over numerous times with stop switch held on.. Then started engine after 15 sec had good water flow, then nothing … Shut motor off loosened strainer cap let water flow , rolled engine over again numerous times, started and no water flow! I then took out zinc out on starboard side on engine (oil cooler I think) . Rolled engine over till I got good water flow out from zinc hole, tightened it, started engine and no water flow out exhaust.. I never ran it longer then a couple of minutes… I have no confidence in that the raw water impeller now so I ordered. New one.. I really do not want to chase impeller pieces so I’m going to wait to hear what you all have to recommend… It’s definitely a learning curve on a new to us Boat.. Never had a issue with last boat with Hino’s.

 

[DavidM]

With a good impeller it should self prime. My guess is for some reason the r/w pump isn’t working. Bad impeller- doubtful. Busted drive shaft- maybe.

David

 

[Kickback]

All was working fine, I just did not like two spots on raw water hose that had cracking and elected to change it… Now I’m at a loss.. I hate to ruin a new impeller that I’m going to put in when it arrives.. Especially if I find the impeller that is in it is ok,, its only a year old… any tips or tricks.. as for drive shaft I know nothing as Sargent Shultz would say

 

[DavidM]

as for drive shaft I know nothing as Sargent Shultz would say

Easy. Take off the end cap of the pump. Crank the engine for a few seconds. If the impeller turns, the drive shaft is ok.

Long shot though!

David

 

[Kickback]

Is the drive for the Impeller a Weak Point? Meaning something that has been known to fail? Only 650 hours on engine.

 

[Bacchus]

Easy. Take off the end cap of the pump. Crank the engine for a few seconds. If the impeller turns, the drive shaft is ok.

Long shot though!

David

Is the drive for the Impeller a Weak Point? Meaning something that has been known to fail? Only 650 hours on engine.

David's suggestion is quick & fairly easy.
The other option is to pull the pump for check out and impeller replacement.
I've never done it that way but many claim it is easier than pulling / replacing the impeller w pump installed. It certainly allows a more thorough inspection / rebuild if any problems identified.
I believe it is only 4 bolts... not sure if there is a gasket involved that should be replaced.

 

[DavidM]

There are only four bolts, but one of them is an absolute @#$& to get to and impossible with big, fat fingers. Fortunately I have short skinny ones.

David

 

[Comodave]

Ok, now you are bragging…

 

[Shrew]

How long are you letting it run before shutting it back off? It takes a while to get through the entire system and out the exhaust.

 

[jleonard]

Also put some grease on the strainer top o ring to make sure you are not sucking air rather than water

 

[Kickback]

The Last time I tried I let engine run for 2 minutes. Because I did not see any signs of water flow I turned off the engine. Mainly because I'm new to this engine and did not want to have to hunt for Impeller pieces in case that was the issue. Even though before I elected to change the raw water hose all was fine.. I have new impeller coming and will be changing it out.. Is there tips and tricks to get water to flow ? On my last boat I used dish soap to lube impeller when I changed them. The soap suds was a good tell tale .

 

[Kickback]

Update
Pulled R/W pump removed impeller and it was toast.. got most of pieces out with a shop vac. Impeller said Johnson but it seemed brittle , I was told by Previous owner that it was changed yearly.. Obviously it was not. or he was told it was changed.. Now I think I should flush raw water system with vinegar since I have pump off. Any suggestions?

 

[Comodave]

I have used Barnacle Buster with good success.

 

[DavidM]

Barnacle Buster diluted 50/50 will work much, much better than vinegar. Take it from a retired ChE who worked in the industrial chemical cleaning industry early in his career.

David

 

[Kickback]

Good Advise, Thanks
Jerry

 

[Kickback]

370 yanmar raw water path of flow ? Does anyone have or know where I can find a schematic of the water flow?

 

[DavidM]

Here is my vague remembrance of how it works:

Water flows from the R/W pump to the main heat exchanger. From there it goes to the transmission cooler, then to the after cooler, then to the lube oil cooler and then to the R/W injection elbow. You can follow that path with your own engine to confirm it.

David

 

[MBythewood]

Attached are screen shots from the 6LYA parts manual. It may help you understand the sea water cooling system flow.