i have a 2qm15 in a 79 hunter 33 that runs perfectly if started with the raw water intake closed and water pumped out of the engine before killing it. if i attempt to start the engine with the raw water valve open, water enters the cylinders and trickles from the air intake. if the engine is killed with water in it, the raw water valve must be shut, and then grind with the starter it until the water is pumped from the cylinders. once it starts, i can open the water flow, and it runs like a champ. attempted solutions: removed and examined head for cracks, changed one injector, and replaced head gasket. after that failed, sandblasted and examined exhaust manifold for cracks. changed mixing elbow. also bypassed entire raw water mixing and let engine drain freely. nothing solved the problem. my best guess is that the mechanic that examined the head missed a crack; however, i am open to test any suggestions before i tear into the head again. thanks.
2qm15 water in air intake
- Thread starter mdhenrich
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Compression release
Does your compression release shut fully? HOw about valve adjustment, is there enough lash to allow your valves to seat fully? Do you have a vented loop in your system? Just some thoughts. hth
Does your compression release shut fully? HOw about valve adjustment, is there enough lash to allow your valves to seat fully? Do you have a vented loop in your system? Just some thoughts. hth
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How far below the water line does your engine sit? Is your exhaust elbow also below water line. Do you have a anti siphon on the water line leading to the mixing elbow? This hould have the anti-siphone valve and be about 2 feet above water line.... Just my thoughts, I am not a mechanic. Also, try the yanmar list on Yahoo....Some good mechanics there Good luck
How far below the water line does your engine sit? Is your exhaust elbow also below water line. Do you have a anti siphon on the water line leading to the mixing elbow? This hould have the anti-siphone valve and be about 2 feet above water line.... Just my thoughts, I am not a mechanic. Also, try the yanmar list on Yahoo....Some good mechanics there Good luck
Plugged aniti-siphon vent
I had a friend with a Catalina/Universal that had the same problem. We traced it to a clogged anti-siphone vent. We he shut it down, the vacum didn't break and it would siphon fresh water in to the engine. The startup is likely caused by same.
I had a friend with a Catalina/Universal that had the same problem. We traced it to a clogged anti-siphone vent. We he shut it down, the vacum didn't break and it would siphon fresh water in to the engine. The startup is likely caused by same.
Intake manifold leak
I'll bet that on cool mornings you get a LOT of steam from the exhaust. While the intake manifold does not have a water passage through it, a crack in one of the block side intake ports can leak into the manifold. Most folks don't check the intake/exhaust ports when checking the head as they don't crack much. When you took the head off was one piston and cylinder head extremely clean? That would be the intake port that is leaking. Water turning to steam and "steam cleaning" the inside of the cylinder. She runs because the water jacket does not get put under much pressure and the leak is small compared to the volume of air going into the engine. I'd pull the intake manifold and have someone crank the engine while you hold the compression release (to keep her from starting, and yes Martha a diesel will run without an intake or exhaust manifold) and look for water leaks. For the record a pressure tester only works on a sealed system. Since you have a raw water system there is no way to attach a pressure tester to it (I know you know this mdhenrich). You could plug the mixing elbow line coming from the engine and let the raw water pump pressurize the block but that may damage the inpeler. You should be OK with just cranking it though.
I'll bet that on cool mornings you get a LOT of steam from the exhaust. While the intake manifold does not have a water passage through it, a crack in one of the block side intake ports can leak into the manifold. Most folks don't check the intake/exhaust ports when checking the head as they don't crack much. When you took the head off was one piston and cylinder head extremely clean? That would be the intake port that is leaking. Water turning to steam and "steam cleaning" the inside of the cylinder. She runs because the water jacket does not get put under much pressure and the leak is small compared to the volume of air going into the engine. I'd pull the intake manifold and have someone crank the engine while you hold the compression release (to keep her from starting, and yes Martha a diesel will run without an intake or exhaust manifold) and look for water leaks. For the record a pressure tester only works on a sealed system. Since you have a raw water system there is no way to attach a pressure tester to it (I know you know this mdhenrich). You could plug the mixing elbow line coming from the engine and let the raw water pump pressurize the block but that may damage the inpeler. You should be OK with just cranking it though.
Im with Bill.....
Check out the exhaust manifold NOW. They do develop 'slab rust' internally and then can quickly develop pin holes between the 'gas side' and the 'water side'. Remove the manifold. Attach the water inlet to house water, block the water outlet, turn on 60 psi pressure from the house supply .... and watch for 'drips' from the gas side. If so, then, buy a new manifold. Youll need a single copper manifold exhaust header 'gasket' from your Yanmar dealer to replace when you reinstall. Another possibility is if you are using the 'stock' exhaust manifold *outlet casting* (its an iron casting that is bolted on to the exhaust manifold outlet and its **attitude is 45 degrees 'down' as it continues**) .... there may not be enough 'head height' to your exhaust system .... and when the engine cools down it 'may' be siphoning water BACK from the water lift muffler. So, if you have this casting thats goes at a 45 degree down angle into a water lift .... consider to modify the exit run of exhaust gases to a 'higher lift' ... easily done by: buying a Yanmar "exhaust manifold to NPT PIPE Adapter, then iron Pipe elbow (up) short run of iron PIPE (UP), pipe elbow ... to Yanmar (aluminum) water injection 'combination elbow/nozzle' ... then connect to rubber exhaust tubing to the water lift. You can add insulation/lagging to this 'riser' to keep the boat cool ... this lagging is available in 2" wide rolls from most Yanmar/diesel engine distributors. Inotherwords you may need to put in an additional 18"-24" of *height* to your exhaust system before it "goes down" to the waterlift to prevent the cooling-down engine from sucking the water lift muffler contents back into the cylinders -- pretty common with Yanmars that use that "45 degree down tailpiece" bolted to the exhaust manifold.
Check out the exhaust manifold NOW. They do develop 'slab rust' internally and then can quickly develop pin holes between the 'gas side' and the 'water side'. Remove the manifold. Attach the water inlet to house water, block the water outlet, turn on 60 psi pressure from the house supply .... and watch for 'drips' from the gas side. If so, then, buy a new manifold. Youll need a single copper manifold exhaust header 'gasket' from your Yanmar dealer to replace when you reinstall. Another possibility is if you are using the 'stock' exhaust manifold *outlet casting* (its an iron casting that is bolted on to the exhaust manifold outlet and its **attitude is 45 degrees 'down' as it continues**) .... there may not be enough 'head height' to your exhaust system .... and when the engine cools down it 'may' be siphoning water BACK from the water lift muffler. So, if you have this casting thats goes at a 45 degree down angle into a water lift .... consider to modify the exit run of exhaust gases to a 'higher lift' ... easily done by: buying a Yanmar "exhaust manifold to NPT PIPE Adapter, then iron Pipe elbow (up) short run of iron PIPE (UP), pipe elbow ... to Yanmar (aluminum) water injection 'combination elbow/nozzle' ... then connect to rubber exhaust tubing to the water lift. You can add insulation/lagging to this 'riser' to keep the boat cool ... this lagging is available in 2" wide rolls from most Yanmar/diesel engine distributors. Inotherwords you may need to put in an additional 18"-24" of *height* to your exhaust system before it "goes down" to the waterlift to prevent the cooling-down engine from sucking the water lift muffler contents back into the cylinders -- pretty common with Yanmars that use that "45 degree down tailpiece" bolted to the exhaust manifold.
thanks for responses
thanks for all the responses. i think i ruled out any exhaust issues by allow the water supply to bypass the exhaust. of couse, this was done after removal of the exhaust and replacement the elbow etc. and the 79 bucks for copper gaskets and thermostat. it was a lesson to be more zen instead of needlessly tearing into things. the guy who helped with the head job did make comments concerning the clean the cylinder head. i thought that was good news. the soot from difficult starting masks any visible steam. i will remove the intake and check for leaks. matthew
thanks for all the responses. i think i ruled out any exhaust issues by allow the water supply to bypass the exhaust. of couse, this was done after removal of the exhaust and replacement the elbow etc. and the 79 bucks for copper gaskets and thermostat. it was a lesson to be more zen instead of needlessly tearing into things. the guy who helped with the head job did make comments concerning the clean the cylinder head. i thought that was good news. the soot from difficult starting masks any visible steam. i will remove the intake and check for leaks. matthew
md; sounds like what happened to my 1979 2qm15
this is exactly what happened to mine. no cracks in head but over time it rusted or corroded, take your pick, through the head and had a couple of pin holes which allowed water to drain down into clyinders. the biggest problem is that a new head is very expensive about a thousand bucks and heads for this engine in good condition are extremely hard to find. i got very lucky on mine and found a used engine in Maine that had been converted to fresh water cooling early in its life. internal rusting definitely kills this particular engine before its time. BTW make sure you keep the exhaust manifold clear and clean of rust. if it goes that's the end, as yanmar no longer sells the part and hasn't for several years. i don't know how long you plan on keeping said engine but you might seriously want to consider converting it to fresh water cooling. S/V Que Pasa?
this is exactly what happened to mine. no cracks in head but over time it rusted or corroded, take your pick, through the head and had a couple of pin holes which allowed water to drain down into clyinders. the biggest problem is that a new head is very expensive about a thousand bucks and heads for this engine in good condition are extremely hard to find. i got very lucky on mine and found a used engine in Maine that had been converted to fresh water cooling early in its life. internal rusting definitely kills this particular engine before its time. BTW make sure you keep the exhaust manifold clear and clean of rust. if it goes that's the end, as yanmar no longer sells the part and hasn't for several years. i don't know how long you plan on keeping said engine but you might seriously want to consider converting it to fresh water cooling. S/V Que Pasa?
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