Yanmar YSM 12 Cooling problems

[diax]

Dear Sirs, on my Yanmar engine I am discovering the following problem: No water is ejected, water is ejected, no water is ejected and so on. The cover of the pump is brand new, impellor is brand new and original, all cooling water pipes have been replaced, the seawater filter has now a position much lower than before - so that the pump has an easier job to do.

Somehow it seems to work, but I think that there must be another reason for this erratic fault.

Otherwise the engine is as reliable as loud.

What is the right thing to do. New pump?

I thank you in advance for your kind support.

diax

[jimbunyard]

If you mean the water is pulsing from the exhaust outlet, say every 2 or 3 seconds, this is normal and an operating characteristic of a water lift muffler system.


If you mean that the pump sometimes works and sometimes doesn't, given all the changes you've made, the last thing to check would be the cam in the pump. I have seen pumps that, even though they looked OK, were just worn out.


You might double check that there is no air leak in the suction side of the system...

[diax]

jimbunyard I thank you for your message.

I have explained myself not correctly the pump is sometimes working and at other times not. We checked for airleaks and replaced in intake valve and all waterpipes.
The pump cover is new, impeller and sealing original Yanmar. Sorry, english is not my native language, what do you mean by "the last thing to check would be the cam in the pump". We did not replace the cam. Should we do so? Thanks for your clarification.

Could it not be another problem in the cooling system behind the pump that unables the cooling water to flow continously?

It is 1 circuit cooling water system.

The engine is about 40 years old.

I am thankfull for any comments.

Diax

[GordMay]

Greetings and welcome aboard the CF, Diax.

[JerryKam]

I have the same engine in my Yamaha 30 and almost on the day 12 years ago had the same problem, that coused overheating and eventually engine rebuild. Installed new impeller into the original pump and it worked for a while, then we noticed no water from the exhaust, took the pump apart all looked good, assembled and checked for obstruction, nothing found. Started the engine and the same happened again and again, and after about 5th disassembly noticed that brand new impeller was spinning without the backing plate and not with it. What happened that the rubber part delaminated from the centre bronze and would not spin when sandwiched with backing plate. It's very hard to see, but check it out. I was lucky that I kept the old impeller as a spare and we made it home.
Cheers and keep the old iron wind going.

[Brewgyver]

You might want to look at a video of normal exhaust water flow:

https://www.youtube.com/watch?v=8YmB2U3dsOo

Running at idle speed, you might have several seconds between "batches" of water coming out.

As Jimbunyard said, this is a normal characteristic of a water lift muffler, but it can look strange if you haven't seen it before. If your exhaust looks like this, and the engine maintains normal temperature, you don't have a problem.

[Compass790]

Hi Diaz,Same thing happened to me as Jerrycam. Be sure you lube the impeller when installing with the lube supplied or silicone grease. The cover clearance is critical but you used the original yanmar gasket or -ring so you should be ok there unless it's worn badly. On some pumps you can flip the cover over if it's worn but not sure about yours. Another possibility is bits of old impeller are clogging the cooling passages but unlikely. Not sure how the drive pulley is connected to pump shaft but check that too. On a lister-Petter motor I had it was just a grub screw & it was slipping on the shaft. I have a YSM8, noisy shakey beasts for sure but extremely long lasting if well maintained.
Let us know please if you find the fault.

[Compass790]

Oh sorry if I'm stating the obvious Diax but drive belt on water pump is not slipping I assume.

[PaulMarion]

Hi diax, Obviously there are many things that can cause this problem and you have covered quite a few. I certainly would look at the pick up through the hull of the boat. Depending if this is via a sail drive unit or through hull inlet, there's always possibilities of a blockage or barnacle build up there or in the tubing. Often the sea cock needs to be checked at the motor end including the tubing on the seaward side too. Close the cock, then remove the hose keep a bucket and rags handy, open the cock and push fencing wire into it and work it around to make sure that no junk is restricting water into the boat. You must find out if water is available to the pump FIRST, then after that confirm the water is being pumped to the motor NEXT. Hope this helps to start with, Regards, Paul.

[JD-MDR]

I had to replace the mixing elbow. It was restricting a lot of water. On my new boat there is a small elbow reducing the half inch hoses to 1/4" at the mixing elbow that I have found clogged two times already. I just flushed the system out forwards and backwards with rydlime. I removed the impellar and the thermostat and circulated the solution for a couple hours