Yanmar 2GM20F cooling problem

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stuendan

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Jun 6, 2020
41
Hunter 326 Hasting, Westernport Bay
Got the boat back in water with antifoul, prop speed and new cutlass bearing + 2 new stop cocks (ball valves) to replace ones on the kitchen sink and Macerator out thru hulls ( both were jammed open and the handles sheared of while trying to free them up :( )While out of the water, I also cleaned out the cooling water strainer! :rolleyes:

When leaving marina, the exhaust had that "different" sound and I got to the end of the channel into clear water as the over temp alarm sounded! Dropped the pick and pulled the input hose of the water pump - plenty water flow! Pulled off the water pump expecting to find a destroyed impellor but all good. :oops: Greased up the impellor with vaseline and it turned easily with impellor blades folding in as expected! Popped it back on and pulled off pipe at heat exchanger - started it up and plenty of flow into under engine sump. Reconnect and take off pipe at rear of heat exchanger - still plenty of flow - reconnect everything and start up - exhaust sounded normal so proceeded off watching water temp gauge - steady at 75 Celsius.

Lesson, if you drain the cooling water while up on the hard, expect an air block and no cooling :huh:!
 
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Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,158
Hunter 310 West Vancouver, B.C.
stuendan said:
Greased up the impellor with vaseline and it turned easily
Click to expand
Not the end of the world but better to use a soluble lubricant on the impelor.

Maybe you were just plain unlucky but I've never lost prime to the pump after being on the hard, even after spending one winter on the hard.
 
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markwbird

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Nov 26, 2012
1,654
C&C 40-2 Berkeley
That really should not happen. It's a self priming pump. Just to be thorough you might check the exhaust elbow where the raw water hose attaches to it for soot. Soot can build up here and block the water entering into the elbow. Pull the hose off and see if it is blocked. If so, try clearing it with a screw driver.
 
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S

stuendan

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Jun 6, 2020
41
Hunter 326 Hasting, Westernport Bay
Looks like my experience is not that unusual! Yanmar water-pump priming | YBW Forum

Probably down to air leaks in water input line joints or the pump seals :(. I'm going to clean up the pump cover plate, replace the impellor and tighten all the input pipe connections. I shouldn't have a problem until next time I clean out the strainer (thereby emptying the inlet pipe). My real concern is not being able to view the exhaust outlet and having to rely on the different exhaust note (H326 exhaust under the stern :oops:). I know that some people have put a flow gauge in the inlet pipe and I have purchased one although I am concerned that the turbine wheel in the gauge is just adding another place to for block ups (although now I would at least have a warning)
Another option is to fit an exhaust outlet in the transom just above the water line!
 
Tally Ho

Tally Ho

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Jan 7, 2011
5,450
Oday 322 East Chicago, IN
stuendan said:
Looks like my experience is not that unusual! Yanmar water-pump priming | YBW Forum

Probably down to air leaks in water input line joints or the pump seals :(. I'm going to clean up the pump cover plate, replace the impellor and tighten all the input pipe connections. I shouldn't have a problem until next time I clean out the strainer (thereby emptying the inlet pipe). My real concern is not being able to view the exhaust outlet and having to rely on the different exhaust note (H326 exhaust under the stern :oops:). I know that some people have put a flow gauge in the inlet pipe and I have purchased one although I am concerned that the turbine wheel in the gauge is just adding another place to for block ups (although now I would at least have a warning)
Another option is to fit an exhaust outlet in the transom just above the water line!
Click to expand
My exhaust exits the boat on thr transom above the water line. It is very reassuring to be able to turn around and see the flow of water. And easier to hear any changes in the tone of the exhaust.

4F63444A-D6C4-47C2-B38D-28840D311B24.jpeg

My first boat (Hunter 280) had an exhaust that exited the boat below the waterline… that was really a challenge.


Greg
 
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John T1594

John T1594

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Jun 4, 2004
834
Hunter 340 Forked River, NJ
Just to be complusive, I would always fill my sea-water strainer and raw water hose with water before starting the engine for the first time each season.
 
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Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,158
Hunter 310 West Vancouver, B.C.
stuendan said:
I know that some people have put a flow gauge in the inlet pipe and I have purchased one although I am concerned that the turbine wheel in the gauge is just adding another place to for block ups
Click to expand
That's what the inlet strainer prevents. The flow indicator relies on an internal magnet in the flow stream which is pushed forward to break an external electrical contact. No internal turbine.

I'd be looking for an air leak on the suction side of your raw water pump. Not once in 24 years has my pump failed to prime even after sitting for weeks out of water and in one case an entire winter on the hard. As @markwbird has said , it's a positive displacement pump and will always prime itself. As final proof that it's not the fault of the pump, check its elevation relative to the water line. If it's like mine, it's a good foot below the water level.

It is IMPOSSIBLE for that pump to not prime when hitting the water after a haul out. This assumes all hoses are in good condition.

stuendan said:
I know that some people have put a flow gauge in the inlet pipe and I have purchased one
Click to expand
Go ahead and install the flow sensor (with a loud alarm) as a guard against such things as forgetting to open the thru-hull and a broken belt and then forget it.
 
BigEasy

BigEasy

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Jun 21, 2004
2,772
Beneteau 343 Slidell, LA
Ralph Johnstone said:
It is IMPOSSIBLE for that pump to not prime when hitting the water after a haul out. This assumes all hoses are in good condition.
Click to expand
The pump will prime; however, if there is air in the lines, that's a problem. May take awhile for the air to purge itself, meanwhile, you're running hot. Had it happen once when I changed the raw water impeller on a 2GM20F. Also had a problem with air in lines after changing coolant; however, that's a separate & closed part of the cooling system. Has never happened on a haulout; however, I am usually out for a few weeks only.
 
Ralph Johnstone

Ralph Johnstone

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Jan 4, 2006
7,158
Hunter 310 West Vancouver, B.C.
I have no way of knowing what's in the sea water line to the pump but, after being out on the hard for a few days, it takes one to two seconds for the pump to prime. How:

1646068071211.png


A flow sensor a foot upstream from the pump.

Same thing when I open up the raw water line when clearing crap from the thru-hull, seconds at most. The 2GM20F moves about 6 USGPM which is like a bat out of hell in a 3/4" line.
 
S

stuendan

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Jun 6, 2020
41
Hunter 326 Hasting, Westernport Bay
Thanks Ralph, can you tell me the brand and source of your flow sensor?

As per "Big Easy" and the guy from the UK on the YBW forum who's boat dries out at low tide , the water pump has no problem shifting water, but not so effective with compressible air! If the raw water input line is completely drained back to the thru hull, the pump will take some considerable time at low revs to evacuate the air in the line and prime. It's got to fight the exhaust back pressure back too.

If I ever need to drain it again, once back in the water, I'll open the line at the pump inlet and purge the air before starting the engine.
 
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