E333 Engine cooling problem

[Blue Moon]

I have an intermittent problem causing engine overheat due to loss of sea water cooling circulation. This is with a Yanmar 3GM30F. I have already checked and claened the sea water strainer, (no blockage), replaced the water pump impellor, (nothing wrong with old one), checked all lines, etc. for blockage. After I get the pump primed and working again, everything is ok. This usually occurs when starting the engine after sailing witha good amount of heal and / or bouncing due to chop. More information.. The sea water strainer is factory mounted high enough above the water line that water will not free flow to the pump. Piping runs from seacock through the strainer to the sea water pump, then to the heat exchanger, then runs to the stean locker and up through an anti-siphon u valve, then back down to the engine compartment and up into the exhaust mixing elbow. Can anyone tell me why the hoses and antisiphon valve, (also appearing to be factory installed), is there? This is not shown on the Yanmar engine cooling diagrams. Also, any other suggestions? I am leaning towards the following... 1) Replace and lube the impellor again. 2) Removed the hoses and anti-siphon valve, piping directly from the heat exchanger output to the mixing elbow. 3) Disassemble and clean the heat exchanger.
Thanks for any suggestions and help.

 

[treilley]

I have seen a few things cause these type of problems.

- An air leak upstream of your pump. Could be hoses or a bad seal on the strainer. Hoses and rebuild kits are cheap.
- A worn impeller cover.

 

[Blue Moon]

Thanks, I will check those out. I was focusing more on the pump output.

 

[Emerald]

This usually occurs when starting the engine after sailing witha good amount of heal and / or bouncing due to chop.

I've had this happen to me on several boats, including Atomic 4 powered as well as Yanmar powered. In both setups, water pumps etc. were all new or rebuilt, strainers on centerline etc. I ended up deciding I really was bouncing the water out of the system and loosing all prime and started shutting the seacock on the engine intake when I was in situations of sustained heel in 20+ degree range and chop as you describe. Once I started doing this, I never had the problem. I figured the through hull for the intake was either bouncing out of the water or just reaching such a high point that the line to the strainer, which in both cases was mounted above the waterline on center, was just draining back out and that the little water pump just couldn't easily generate enough lift to reprime easily. I say easily, as I did get it to reprime sometimes by giving a little increase in RPM, but that's a catch 22 on just burning up the impeller if it's starving for water for lubrication.

It would be interesting to know how many others have had this problem and if they also felt it was due to back draining. My best guess, and worth what you paid for it

 

[jmcpeak]

I've had a similar problem with my 5424.

Probably pumps water very well at the dock right?

Put in a fresh thermostat - only around $30.

Clean the heat exchanger - there is a good write up somewhere on how to do this with muriatic acid - Google it.

That took care of my problem. - I think it was probably the heat exchanger.

Good luck!

Jason