For the first time in 20 years my engine wouldn't start this weekend. It kept catching, so I kept cranking--too long maybe, since it usually starts right up (sometimes on second 20 second crank when really cold) I'm aware that if one cranks the engine too long exhaust water can get sucked up into the cylinders since there is no exhaust. This is a fresh water cooled system, so raw water flows through a heat exchanger, then into the mixing elbow and out through the exhaust line & muffler. Can water can backflow from the elbow into the cylinders with this configuration? If so, what is the fix? Many forum mention not over cranking, but but I can't find the fix if one has. Can one just disconnect the exhaust line from the mixing elbow, drain it and start over?
Yanmar 2GM20f may have cranked too long
- Thread starter Dean Strong
- Start date
The problem is that you could have water on top of the cylinders (at least1) and when you crank the engine, the water doesn’t compress and…bang…you bend a rod or some similarly disastrous problem. We call it “hydro lock”.
Yes, a 2GM20F is susceptible to the problem.
If you are worried, you can remove the injectors and turn the engine over…I think this would blow any water out of the cylinders without a catastrophic event.
I wonder if opening the decompression levers would also allow the water to be pushed out of the cylinder? I am not sure how exactly the levers decompress the cylinders.
I assume you are in salt water, so if there is water in the cylinders, you need to get it out and maybe get some Marvel Oil in there before things get worse.
A trick for getting these old Yanmars, without glow plugs, to start when they are cold is to heat the air at the air intake…a hair dryer, pointed into the air filter (or remove the filter), holding a lighter or lighter stick down there near the intake, etc. can warm the air enough to get them to fire.
Good luck, I hope no damage has been done, that you can get any water out of the cylinders, and can get her fired up.
Greg
Yes, a 2GM20F is susceptible to the problem.
If you are worried, you can remove the injectors and turn the engine over…I think this would blow any water out of the cylinders without a catastrophic event.
I wonder if opening the decompression levers would also allow the water to be pushed out of the cylinder? I am not sure how exactly the levers decompress the cylinders.
I assume you are in salt water, so if there is water in the cylinders, you need to get it out and maybe get some Marvel Oil in there before things get worse.
A trick for getting these old Yanmars, without glow plugs, to start when they are cold is to heat the air at the air intake…a hair dryer, pointed into the air filter (or remove the filter), holding a lighter or lighter stick down there near the intake, etc. can warm the air enough to get them to fire.
Good luck, I hope no damage has been done, that you can get any water out of the cylinders, and can get her fired up.
Greg
I can certainly feel for you. If you did overcrank, getting get rid of any water in the cylinders is a whole 'nother subject that someone else here can explain.
If you experience any problems in starting, close the thru-hull valve to the engine. The pump is full of water so it's safe for a minute +/- of cranking. Also try wetting your rings by cranking for 10 sec. with the stop pulled out. Then try normal starting. Wet rings give better compression.
! At that point, the water is well above any open exhaust valve where water will backflow to when the engine is shut down before the next cranking session begins. Water in a cylinder is an unknown at this point but cranking the engine may prove disastrous.
Any particular reason you think there is water in a cylinder other than time spent cranking.
If you experience any problems in starting, close the thru-hull valve to the engine. The pump is full of water so it's safe for a minute +/- of cranking. Also try wetting your rings by cranking for 10 sec. with the stop pulled out. Then try normal starting. Wet rings give better compression.
A little nastier than that. It's the internal loop at the end of the exhaust hose that causes all the grief. The pump will keep pumping water into the exhaust hose until it's the height of the internal loop
! At that point, the water is well above any open exhaust valve where water will backflow to when the engine is shut down before the next cranking session begins. Water in a cylinder is an unknown at this point but cranking the engine may prove disastrous.Any particular reason you think there is water in a cylinder other than time spent cranking.
You will know if there is water in even one cylinder; it just will not turn over no matter how strong your battery is. Greg is quite correct, you can remove the injectors and turn the engine over. however, It will spew water all over the place, so cover the engine with a very heavy cloth tarp or rug to contain the water. There's a whole lot of compression pushing that water out.
A decompression lever opens the exhaust valves a tiny bit, which could solve the problem. All boat engines should have them, because once a diesel is turning without compression, it should start on a very weak battery.
Immediately after removing the water, spray in a good lubricant like Marvel Mystery oil in the injector holes and spin the engine over to lubricate the cylinders and rings. Replace the injectors and run the engine right away, for at least 10 minutes. But first check your oil. If it is like coffee with cream, it indicates you have some bad rings and there is water in it. It must be changed at least twice to insure you have gotten all the water out of the lubrication system.
There probably is a drain on your muffler. Before you try cranking again you should empty the exhaust system of sea water with that drain.
Easy.. Remove the air cleaner, Pull the compression releases on both cylinders. Then disconnect the drain hose at the engine; when you pull the hose off, water will drain from the hose . Then close the raw water inlet valve . THEN spin the engine over for 15-20 seconds to clear it of water. After the water is blown out, start the engine normally..... The exhaust hose is still off so it will smoke up the place pretty well. Don't let it run for more than 3-4 seconds; reinstall the exhaust hose and air cleaner, turn the raw water valve back on, and start it normally and let it run for 5-10 minutes or so until it is warmed up. Check the oil and if it shows any milkiness, change it and the filter. If the oil looks OK, or you've changed it, take the boat out for a motor trip of a half hour or so.. All good!
Which hose is this ? Raw water outlet from the heat exchanger or ........... ?
The raw water circuit is at a lever well above the exhaust outlet of the engine so no removal of the raw water from up there.
Otherwise, sorry, don't see where you are indicating.
Rum in the exhaust hose you say ? Absolute sacrilege.
Sacrilege aside, the exhaust riser would still be full of raw water after the exhaust hose was pulled off.
BUT, if you pulled the hose off first just to drain it (keep your sox dry) and THEN slid the cast iron riser back a bit, that would completely drain the volume outside of the exhaust valves.
I would then feel much safer in pulling injectors, opening compression levers, etc, etc, or whatever would be next in line after ensuring all the water has been removed from outside the exhaust valves.
I'd rather move heaven and earth and avoid getting into that position in the first place
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I agree, Ralph..
From experience, the engine will clear of that residual water when decompressed and spun over briskly. It will clear through the intake side, so removing the air filter is important. Once cleared, the engine should be started and run for a while to dry things up and get the water out of the rings.. OP is in salt water, I think, so if the engine was not cleared and dried that same day, he will have issues with corrosion that may require pulling the injectors. Speed of correction is really important when dealing with salt water in the engine.
From experience, the engine will clear of that residual water when decompressed and spun over briskly. It will clear through the intake side, so removing the air filter is important. Once cleared, the engine should be started and run for a while to dry things up and get the water out of the rings.. OP is in salt water, I think, so if the engine was not cleared and dried that same day, he will have issues with corrosion that may require pulling the injectors. Speed of correction is really important when dealing with salt water in the engine.
NOTE: "overheating the starter motor is the #1 reason for failure. never run the starter motor more than 15 seconds. then wait a full 2 minutes for it to cool down"
best to never run the starter for more than 5 seconds and let cool down
if engine does not start on first try, turn off water inflow before more tries
best to never run the starter for more than 5 seconds and let cool down
if engine does not start on first try, turn off water inflow before more tries
My 2GM20F starts in cold air pretty reliably if I use full throttle, then immediately back it off when it starts. But it sure doesn't like cold air (below 60 or so..).
The reason for hydrolock is seawater backflow into the engine from the wet exhaust system. The primary reason for this is the standard design for the exhaust system includes a a substantial riser just before the exhaust exit at the stern. This riser is specified in the ABC code to prevent following seas from entering the usual transom located exhaust port and filling the exhaust system. However, the code fails to address the problem this riser causes during extended cranking. In many, if not most, engine installations the engine exhaust port is lower than the riser top. During extended cranking the entire exhaust system fills with seawater and immediately upon releasing the starter button that seawater runs back by gravity from the riser to the lower engine exhaust port flooding the engine. While in many cases raised mixing elbows are available for your engine and some may fit in the available engine space, they are often not present. Compare your engine exhaust port "spill point" to your stern riser "spill point" and you will likely see this defective design in your boat.
This is an interesting thread and the hydrolock boogeyman sometimes finds me during a cold start or when I'm bleeding diesel lines. All the great information above prompted me to have a look at Nigel Calder's "Marine Diesel Engines" where he discusses this briefly, early on in chapter 4.
As mentioned already several times above, he suggests using decompression levers and recommends using a hand crank to slowly turn the engine over and push out the water from the cylinders. The OP's 2GM20F has decompression levers and so obviously that seems like a good option.
Calder also suggests injector removal if the engine doesn't have decompression levers, but advises against this for amateurs citing difficulty and potential for damage. His alternative tips when there are no decompression levers were interesting. First he suggested that water might be able to be forced through cylinders on engines with some wear on them by simply turning the engine over slowly bit by bit (while preventing the engine from starting of course). The other suggestion was to remove the valve cover and push a quarter in between the tops of the valve stems and the rocker arms for the exhaust valves and then slowly turning the motor over.
As mentioned already several times above, he suggests using decompression levers and recommends using a hand crank to slowly turn the engine over and push out the water from the cylinders. The OP's 2GM20F has decompression levers and so obviously that seems like a good option.
Calder also suggests injector removal if the engine doesn't have decompression levers, but advises against this for amateurs citing difficulty and potential for damage. His alternative tips when there are no decompression levers were interesting. First he suggested that water might be able to be forced through cylinders on engines with some wear on them by simply turning the engine over slowly bit by bit (while preventing the engine from starting of course). The other suggestion was to remove the valve cover and push a quarter in between the tops of the valve stems and the rocker arms for the exhaust valves and then slowly turning the motor over.
Interesting. So the water goes past the rings into the crankcase?
I'll have to check that out. The book is on the boat. Hope I never have that problem though.
The rings on a diesel are a little loose until the engine heats up. This is why the oil turns so black and why it is not good to run the engine at idle speeds or unloaded for a long time. My Yanmar will blow some light blue smoke when it starts up, once it is warm there is no smoke. The smoke is from oil blowing by the rings and burning.
Can anyone point to literature which indicates whether Yanmar compression unloaders control inlet or exhaust valves ? I can't wring either out of my Yanmar shop manual. Thanx.
Hey, I found it!
From "YANMAR DIESEL INBOARD SHOP MANUAL" ("Yanmar GM Shop Manual Part 2" in the SBO Downloads), Chapter 6, p. 102, "The decompression mechanism on the valve cover forces the exhaust valves open to reduce compression pressure in the cylinders."