I have a Yanmar YSM-12, one cylinder in a 30 ft Catalina & have a mystery re overheating. At the dock, starts up & running out of port runs cool as it is designed to do. After sailing for several hours, Start the engine & very little water out the exhaust & the hot light comes on. after several shut downs & restarts, all is well. Have checked all the hoses for blockage, OK. so any thoughts on this? Thanks
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Sounds like your pump may be worn
I had a similar issue with my YSM12. The water pump itself was worn and air was entering the system...not the impeller. The housing plate was the culprit. I replaced the entire pump and all is well! Rob
I had a similar issue with my YSM12. The water pump itself was worn and air was entering the system...not the impeller. The housing plate was the culprit. I replaced the entire pump and all is well! Rob
Belt tight?
Heat soaking might cause a loose belt to not drive a pump but you said it happened after several hours of sailing so it should be cool. Robs idea is better than mine.
Heat soaking might cause a loose belt to not drive a pump but you said it happened after several hours of sailing so it should be cool. Robs idea is better than mine.
Pump impeller
I would check the pump impeller if the rubber and metal bushing became separated. This happened to me once.
I would check the pump impeller if the rubber and metal bushing became separated. This happened to me once.
Prolonged over heating
Check thermostat since some valves after prolonged over heating will fail in the open position and result with a cold engine. ( Yanmar 2GM 13 hp)
Check thermostat since some valves after prolonged over heating will fail in the open position and result with a cold engine. ( Yanmar 2GM 13 hp)
OVERHEATING
I had a similiar problem years ago. A mechanic found the exhaust elbow leading from the block was plugged. New elbow and about half hour no more problems. TIC TAC III 310 catalina
I had a similiar problem years ago. A mechanic found the exhaust elbow leading from the block was plugged. New elbow and about half hour no more problems. TIC TAC III 310 catalina
Pump
If you have checked all the belts and hoses, the raw water pump is the next place to look, as Rob has stated. You might also check the raw water strainer, and make sure there isn't some loose material floating around in there. I have a QM 15 and the only cooling problems I have ever had were due to a bad thermostat. I change the raw water impeller every other year as a matter of routine maint. Most people seem to do this only when they have a problem.
If you have checked all the belts and hoses, the raw water pump is the next place to look, as Rob has stated. You might also check the raw water strainer, and make sure there isn't some loose material floating around in there. I have a QM 15 and the only cooling problems I have ever had were due to a bad thermostat. I change the raw water impeller every other year as a matter of routine maint. Most people seem to do this only when they have a problem.
Very little water out the exhaust
Clearly a raw water flow problem. Since it happens after the engine has been run, shut down and restarted it may have to do with hot soak or heeling. I can't think of any reason why heeling the engine while stopped would cause it to over heat once you start motoring again sooo; Is the engine/engine room warm when you restart it? It is a little known fact that the raw water pump does not get hot until well into the motoring cycle or after motoring for a while and then shutting down. The raw water keeps it cool so you have to hot soak it while the engine is not running to get it to heat up. So what could cause low/no raw water flow when a pump is hot and cause normal flow when the pump is cold or after some water has flowed through it? The drive belt will be cold upon startup, will heat up after your hot soak but will stay hot after you restart the engine so my bet is that is not the problem. The pump housing will be cold when you start and stay cold due to the raw water flow while the engine is running. It will hot soak once you stop the engine and be hot for a while until the raw water once again cools it down. Hay! that is exactly what you described. Sounds like the pump. My bet is the impeller is slipping on the shaft or the access plate/shaft seal has an air leak that only shows up when hot. Reproduce the problem and then coat the access plat mating surface with dish washing detergent. Look for bubbles out the exhaust. If no bubbles then CAREFULLY coat the pump shaft seal and again look for bubbles. If no bubbles then it is surely something on the inside but that can only be the impeller. Happy sailing
Clearly a raw water flow problem. Since it happens after the engine has been run, shut down and restarted it may have to do with hot soak or heeling. I can't think of any reason why heeling the engine while stopped would cause it to over heat once you start motoring again sooo; Is the engine/engine room warm when you restart it? It is a little known fact that the raw water pump does not get hot until well into the motoring cycle or after motoring for a while and then shutting down. The raw water keeps it cool so you have to hot soak it while the engine is not running to get it to heat up. So what could cause low/no raw water flow when a pump is hot and cause normal flow when the pump is cold or after some water has flowed through it? The drive belt will be cold upon startup, will heat up after your hot soak but will stay hot after you restart the engine so my bet is that is not the problem. The pump housing will be cold when you start and stay cold due to the raw water flow while the engine is running. It will hot soak once you stop the engine and be hot for a while until the raw water once again cools it down. Hay! that is exactly what you described. Sounds like the pump. My bet is the impeller is slipping on the shaft or the access plate/shaft seal has an air leak that only shows up when hot. Reproduce the problem and then coat the access plat mating surface with dish washing detergent. Look for bubbles out the exhaust. If no bubbles then CAREFULLY coat the pump shaft seal and again look for bubbles. If no bubbles then it is surely something on the inside but that can only be the impeller. Happy sailing
Classic signs of an exhaust manifold going 'bad'..
Exhaust manifolds are usually iron castings and cast iron is a fairly compatible metal versus sea water ..... However, when cast iron is being made and cools in its mold after its poured with hot metal it 'stratifies' like an onion - layers. Most 'rust' that forms in/on wetted and heated cast iron is black or blue rust which is protective (ferrous oxide). However once the layers of the onion become 'penetrated' (by rust or corrosion) the rust becomes 'red' (destructive) ferric oxide rust between the onion layers (red rust is less dense than iron so it generates a lot of pressure and will 'push' the layers of the onion apart --- and form whats known as "slab rust". Once the stratifications start to break apart, large 'platelettes' of rust will begin to break loose and some of them large enough to block the flow of cooling water through the exhaust manifold .... and when you shut down the engine and water the pressure reduces - the slabs fall to the bottom of the manifold so you can start up again and not notice any problem .... until another slab breaks off (or gets stirred-up from the bottom of the manifold) and blocks the manifold outlet. Next time on the boat, run the engine at cruising rpm (in neutral) and with a bucket and stopwatch -measure how long it takes the exhaust discharge to fill the bucket. Then, when the engine overheats .... and the exhaust manifold is sensibly much hotter than 'normal' repeat the test with a bucket and a stopwatch and if the output flow is considerably less then you probably have a blocked exhaust manifold water circuit caused 'usually' by 'slab rust'. The remedy is to remove the manifold, go into the 'water-side' with a stiff wire and break up all the 'slabs' that you can find, then invert the manifold and shake out all the broken up debris. If you find such 'slabs' you should do a 'pressure hold test' to validate that there arent any *pin-holes* between the water side and the gas side .... which will allow water to drain-back into the Cylinder when the engine is stopped !!!! Take the manifold off the boat and totally block the water outlet; apply a garden hose ***with a pressure gage****, pressurize the manifold to approx 30 psi then close the valve and watch the pressure .... if the pressure is dropping after you shut off the valve then you have a pin-hole and the manifold definitely needs to be replaced or you risk filling the cylinder with water. On large commercial ships to prevent 'slab rust' the engines are shut down ***only*** when absolutely necessary to shut down ...... and most importantly are NEVER allowed to 'dry out'. Its the constant drying then wetting, etc. that makes cast iron 'lose its onion skin' in the form of 'slab rust'. Hope this helps.
Exhaust manifolds are usually iron castings and cast iron is a fairly compatible metal versus sea water ..... However, when cast iron is being made and cools in its mold after its poured with hot metal it 'stratifies' like an onion - layers. Most 'rust' that forms in/on wetted and heated cast iron is black or blue rust which is protective (ferrous oxide). However once the layers of the onion become 'penetrated' (by rust or corrosion) the rust becomes 'red' (destructive) ferric oxide rust between the onion layers (red rust is less dense than iron so it generates a lot of pressure and will 'push' the layers of the onion apart --- and form whats known as "slab rust". Once the stratifications start to break apart, large 'platelettes' of rust will begin to break loose and some of them large enough to block the flow of cooling water through the exhaust manifold .... and when you shut down the engine and water the pressure reduces - the slabs fall to the bottom of the manifold so you can start up again and not notice any problem .... until another slab breaks off (or gets stirred-up from the bottom of the manifold) and blocks the manifold outlet. Next time on the boat, run the engine at cruising rpm (in neutral) and with a bucket and stopwatch -measure how long it takes the exhaust discharge to fill the bucket. Then, when the engine overheats .... and the exhaust manifold is sensibly much hotter than 'normal' repeat the test with a bucket and a stopwatch and if the output flow is considerably less then you probably have a blocked exhaust manifold water circuit caused 'usually' by 'slab rust'. The remedy is to remove the manifold, go into the 'water-side' with a stiff wire and break up all the 'slabs' that you can find, then invert the manifold and shake out all the broken up debris. If you find such 'slabs' you should do a 'pressure hold test' to validate that there arent any *pin-holes* between the water side and the gas side .... which will allow water to drain-back into the Cylinder when the engine is stopped !!!! Take the manifold off the boat and totally block the water outlet; apply a garden hose ***with a pressure gage****, pressurize the manifold to approx 30 psi then close the valve and watch the pressure .... if the pressure is dropping after you shut off the valve then you have a pin-hole and the manifold definitely needs to be replaced or you risk filling the cylinder with water. On large commercial ships to prevent 'slab rust' the engines are shut down ***only*** when absolutely necessary to shut down ...... and most importantly are NEVER allowed to 'dry out'. Its the constant drying then wetting, etc. that makes cast iron 'lose its onion skin' in the form of 'slab rust'. Hope this helps.
Mine was this...
You said in your post that you checked the hoses for blockage, but did you check all of the fittings as well? I had a total blockage on my YSM12 at the fitting that you remove to replace the thermostat. It was a real head-scratcher for me for a while. It looked like nothing was blocked, but no water exiting the tailpipe. I'm just sayin' check the flow from the intake to the exhaust. You'll find the problem. Good luck.
You said in your post that you checked the hoses for blockage, but did you check all of the fittings as well? I had a total blockage on my YSM12 at the fitting that you remove to replace the thermostat. It was a real head-scratcher for me for a while. It looked like nothing was blocked, but no water exiting the tailpipe. I'm just sayin' check the flow from the intake to the exhaust. You'll find the problem. Good luck.
... and another thing:
Check the hose from the raw water intake valve to the engine. When we bought our (used) 1986 Hunter with Yanmar 2GM20F, the said hose had been replace with a standard engine hose, not a steel-wire-reinforced one. When the pump sucked real hard, the hose collapsed and, voila, no water to cool the engine! Good luck, as each post could be the problem.. mine is just a little unusual.
Check the hose from the raw water intake valve to the engine. When we bought our (used) 1986 Hunter with Yanmar 2GM20F, the said hose had been replace with a standard engine hose, not a steel-wire-reinforced one. When the pump sucked real hard, the hose collapsed and, voila, no water to cool the engine! Good luck, as each post could be the problem.. mine is just a little unusual.
Pump loosing it's prime?
The possible problem referred to in previous posts would be in the "mixing elbow" in Yanmar-speak: the exhaust amnifold is not jacketed, but it attaches with a short piece of threaded pipe to a jacketed elbow where the cooling water is injected on the downhill (exhaust) side, just before the point where the rubber exhaust hose is attached. A rust-clogged mixing elbow could be the source of your trouble, but I'd also have a hard look at the water pump. How long since you installed a new impeller? Is the pump cover scored, loose or ??? It may be that the pump is loosing it's prime when you're sailing & heeled over, and due to wear etc it's having some difficulty resuming pumping water when you re-start the engine. Another thing to look at, tho I don't think it's the cause of this problem, is the brass petcock on the underside of the cylinder head. Open it and if no water flows out,unscrew it from the head and poke up with a stiff piece of wire to dislodge any built-up scale or crud inside the cylinder head. The petcock was put there to enable cleaning of a hot-spot in the engine, a point where mineral build-up is most likely to occur in a raw-water cooled system.
The possible problem referred to in previous posts would be in the "mixing elbow" in Yanmar-speak: the exhaust amnifold is not jacketed, but it attaches with a short piece of threaded pipe to a jacketed elbow where the cooling water is injected on the downhill (exhaust) side, just before the point where the rubber exhaust hose is attached. A rust-clogged mixing elbow could be the source of your trouble, but I'd also have a hard look at the water pump. How long since you installed a new impeller? Is the pump cover scored, loose or ??? It may be that the pump is loosing it's prime when you're sailing & heeled over, and due to wear etc it's having some difficulty resuming pumping water when you re-start the engine. Another thing to look at, tho I don't think it's the cause of this problem, is the brass petcock on the underside of the cylinder head. Open it and if no water flows out,unscrew it from the head and poke up with a stiff piece of wire to dislodge any built-up scale or crud inside the cylinder head. The petcock was put there to enable cleaning of a hot-spot in the engine, a point where mineral build-up is most likely to occur in a raw-water cooled system.
I vote for the elbow
Since I had that happen to me with expensive results. It plugged completely and blew hoses everywhere, with exhaust going all through the interior. I checked and found the Yanmar folks recommend taking the elbow apart and cleaning it every 400 hours. Since then, no problems. Sanders s/v Good News
Since I had that happen to me with expensive results. It plugged completely and blew hoses everywhere, with exhaust going all through the interior. I checked and found the Yanmar folks recommend taking the elbow apart and cleaning it every 400 hours. Since then, no problems. Sanders s/v Good News
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