Yanmar 2gm 20f water cooling problem

[CharlesNeilson]

So...at low revs plenty of water is expelled out the back. As soon as i rev to 2000 amount of water reduces to a minimum/none and overheat signal activates fairly quickly. Eg saturday used engine at slow speed to watch an Opti race, no problem, as soon as we revved up engine/increase speed exhaust changed pitch and no expelled water/overheat sensor activated.
I do however notice that at high revs engine whines: high pitch noise that i have never heard before. Could this be a clue??
New impeller, new belt, new impeller gasket, checked all pipes ahead of heat exchanger, not checked anything after exchanger.
Thanks for any help.
Quebec Canada

[Wotname]

Welcome aboard CF, CharlesNeilson.
I suggest checking the heat exchanger itself and if you haven't done so recently, the mixing elbow. The elbow should be checked and cleaned regularly.

[Wotname]

Have you checked the seacock and strainer where the raw water enters the boat and hose to the inlet side of the raw water pump?

Just because there is flow at low RPM, it doesn't mean a blockage is not being sucked into the hose at higher RPM.

[Cheechako]

... did this start after the impeller change? Impeller chunks in the heat exchanger or transmission cooler if it has one...?

[djmarchand]

Originally Posted by Wotname

Have you checked the seacock and strainer where the raw water enters the boat and hose to the inlet side of the raw water pump?

Just because there is flow at low RPM, it doesn't mean a blockage is not being sucked into the hose at higher RPM.

This is my guess for a sudden stoppage of coolant flow at higher rpms.


David

[casual]

Raw water filter is it clean ? Perhaps a piece of debris plastic Saran Wrap might no be visible . Weak hose on suction side increase rpm it closes restricts water flow . I, have seen both of these occur . R U certain raw water thru hull is clear? Remove hose open stick a screw driver thru . Last muffler could be clogged or separated inside restricting flow.
That's all I got.

[Jerry Woodward]

Unless you know the history of the exhaust elbows, replace them. It's not that hard. I did both engines and also checked the heat exchanger as well. The elbows looked pristine on the outside but there was significant rust inside. The problem is that the rust blocks the cooling water as well as the exhaust, so the engine runs like crap. You won't believe how well it will run once you replace it. The elbow is threaded onto a section of pipe which bolts onto the exhaust manifold. I couldn't get that piece separated from the elbow so I took it into a shop where they used a torch and bench vice to get it off.

[SAMUELBURNS]

Charles - My 3YM20 had a similar problem which turned out to be a nearly-plugged exhaust hose. After removing the hose and shaking out years of accumulated exhaust gunk the engine now runs fine . . .

[jimbunyard]

Could also be an internally delaminated pickup hose. One way of troubleshooting is taking the raw water hose off at various points to see how far the water gets before being stopped...

[CharlesNeilson]

Originally Posted by Wotname

Have you checked the seacock and strainer where the raw water enters the boat and hose to the inlet side of the raw water pump?

Just because there is flow at low RPM, it doesn't mean a blockage is not being sucked into the hose at higher RPM.

Many thx for reply. Yes i did. I removed the hose from the entry to impeller and blew thru pipe and it is clear. I then removed hose from entry to heat exchanger, turned engine on and flow increased as i revved up. So i am fairly sure it is post heat exchanger, mixing elbow my next target.

[CharlesNeilson]

Originally Posted by Wotname

Welcome aboard CF, CharlesNeilson.
I suggest checking the heat exchanger itself and if you haven't done so recently, the mixing elbow. The elbow should be checked and cleaned regularly.

Many thx for reply. Yes, mixing elbow is my next target. To my knowledge it has not been cleaned/changed in 15+ years. I have the part number so will see if my local supplier has in stock. Will report back. In meantime its low power out of harbour and sails raised asap.!!!

[CharlesNeilson]

Originally Posted by Jerry Woodward

Unless you know the history of the exhaust elbows, replace them. It's not that hard. I did both engines and also checked the heat exchanger as well. The elbows looked pristine on the outside but there was significant rust inside. The problem is that the rust blocks the cooling water as well as the exhaust, so the engine runs like crap. You won't believe how well it will run once you replace it. The elbow is threaded onto a section of pipe which bolts onto the exhaust manifold. I couldn't get that piece separated from the elbow so I took it into a shop where they used a torch and bench vice to get it off.

Many thx for suggestion. This is exactly my next target. I posted to someone else elbow has not been cleaned/changed in 15+ years, so that is my next job. Will let you kmow progress.

[CharlesNeilson]

Originally Posted by Cheechako

... did this start after the impeller change? Impeller chunks in the heat exchanger or transmission cooler if it has one...?

I later found out i did not change the impeller. But it is in good shape, no fins are missing. But to be on safe side i am going to replace today many thx for reply.

[CharlesNeilson]

Originally Posted by casual

Raw water filter is it clean ? Perhaps a piece of debris plastic Saran Wrap might no be visible . Weak hose on suction side increase rpm it closes restricts water flow . I, have seen both of these occur . R U certain raw water thru hull is clear? Remove hose open stick a screw driver thru . Last muffler could be clogged or separated inside restricting flow.
That's all I got.

Boat does not have a raw water filter, but i am wondering if that is a good addition. Also maybe put some sort of cage attached to hull where water sucked in as a first barrier to entry (right now all there is is a hole). End of last season engine overheated, i opened impeller and clean, but entry to heat exchanger clogged with seaweed. Next target mixing elbow. Many thx for suggestions.

[Jerry Woodward]

Originally Posted by CharlesNeilson

Boat does not have a raw water filter, but i am wondering if that is a good addition. Also maybe put some sort of cage attached to hull where water sucked in as a first barrier to entry (right now all there is is a hole). End of last season engine overheated, i opened impeller and clean, but entry to heat exchanger clogged with seaweed. Next target mixing elbow. Many thx for suggestions.

You absolutely need a raw water strainer to strain out the large junk like seaweed. Otherwise, you will continue to clog your heat exchanger and probably wear out your impellers prematurely. You don't need a screen attached to the outside if you have a raw water strainer. Some people don't like those screens because they can increase the chance of clogging if you don't keep them clean. I have never had a problem with mine.