glocklt4
Member
2005 Merc 5.0 with only 155hrs. Tried to start the boat and engine seized after about a half crank. Found water in two cylinders after pulling all plugs. I'm a car guy and have rebuilt an engine before but still learning specifics with boats, so in my world it would be cylinders 5 & 6 since it's a GM block. In case that is different, they were 2nd from back on both sides of engine.
De-winterized like normal for the past 4 years since I got the boat. Winterization process was to change drive lube, engine oil and filter, fuel filter, fog engine, open all 5 blue plugs on engine block and drain water then put plugs back in and fill engine with -50F deg antifreeze via main coolant hoses. To De-winterize I just check fluids again (and in the future will pull plugs to check for water!), check hoses and start her up with water flowing through impeller. Have never had this problem before with any engine.
Last year in Dallas we were below freezing for about 3-4 days straight, down to 8-10F. No problems with boat last year at all. Same winterization and de-winterization process last year as this year. This year I don't think we were below freezing for more than 8 hours, lowest was upper 20's overnight once or twice. We really didn't have a winter at all... I REALLY don't think it's possible that the block is cracked from frezzing unless it was cracked all last season but still worked fine (only got about 15-20 hours on her due to being out of town a lot).
Water in cylinders was pretty orange and rusty. No water in oil. I have not pulled drain plugs on engine to see if there is oil in the anti-freeze (this could be difficult to identify too). With all plugs pulled, I ran the started for 20-30 seconds listening to the crank/rods for knocking and also the valvetrain for ticking. All sounds good and quiet, so hopefully no damage from trying to start a hydrolocked engine.
My possible options on the cause are:
1) cracked block (but affecting two cylinders on opposite sides??)
2) two head gaskets that leaked into only one cylinder each (maybe coincidence that the two affected are exactly opposite each other)
3) rotten/cracked exhaust riser that leaked antifreeze or undrained water back through exhaust into cylinders
Compression on all cylinders was 105-115psi with one compression stroke except #5 (2nd to back right), which was only 90. I can retest all cylinders with more than one compression stroke but not sure that will make a difference. The times that I did get more than one compression stroke the cylinders were over 140-150psi, including one of the ones that had water in it. So this tells me no valve damage from seize.
So... I am not sure what to do to figure out how the water got in these two cylinders. On a car I'd use a block tester to verify if exhaust gases are getting into the coolant, but that only works on a closed lop cooling system.
After reading here and other forums I am thinking the next step is a leak down test and listen for air escaping when listening down the oil filler tube. That MIGHT indicate head gasket(s) are gone. If no hissing there maybe that indicates possible issue with block.
The other big variable which I just don't understand since I haven't taken one apart yet is the exhaust riser. I have read that it's possible for this to rot and let water in the exhaust. If only cylinders 5 & 6 had their exhaust valve cracked open then this could make sense.. but not highly likely. I just simply don't know enough about how these work.
Also, with all plugs pulled I ran the starter for about 20-30 seconds and listened closely to the small block and the valve train for knocks and ticks. Seems like the seize due to water in the cylinders did not bend anything from my initial investigation. I'm open to any suggestions on other tests to be sure that seizure itself did not cause any problems.
Recommendations on how to figure out how water got in these two cylinders??
De-winterized like normal for the past 4 years since I got the boat. Winterization process was to change drive lube, engine oil and filter, fuel filter, fog engine, open all 5 blue plugs on engine block and drain water then put plugs back in and fill engine with -50F deg antifreeze via main coolant hoses. To De-winterize I just check fluids again (and in the future will pull plugs to check for water!), check hoses and start her up with water flowing through impeller. Have never had this problem before with any engine.
Last year in Dallas we were below freezing for about 3-4 days straight, down to 8-10F. No problems with boat last year at all. Same winterization and de-winterization process last year as this year. This year I don't think we were below freezing for more than 8 hours, lowest was upper 20's overnight once or twice. We really didn't have a winter at all... I REALLY don't think it's possible that the block is cracked from frezzing unless it was cracked all last season but still worked fine (only got about 15-20 hours on her due to being out of town a lot).
Water in cylinders was pretty orange and rusty. No water in oil. I have not pulled drain plugs on engine to see if there is oil in the anti-freeze (this could be difficult to identify too). With all plugs pulled, I ran the started for 20-30 seconds listening to the crank/rods for knocking and also the valvetrain for ticking. All sounds good and quiet, so hopefully no damage from trying to start a hydrolocked engine.
My possible options on the cause are:
1) cracked block (but affecting two cylinders on opposite sides??)
2) two head gaskets that leaked into only one cylinder each (maybe coincidence that the two affected are exactly opposite each other)
3) rotten/cracked exhaust riser that leaked antifreeze or undrained water back through exhaust into cylinders
Compression on all cylinders was 105-115psi with one compression stroke except #5 (2nd to back right), which was only 90. I can retest all cylinders with more than one compression stroke but not sure that will make a difference. The times that I did get more than one compression stroke the cylinders were over 140-150psi, including one of the ones that had water in it. So this tells me no valve damage from seize.
So... I am not sure what to do to figure out how the water got in these two cylinders. On a car I'd use a block tester to verify if exhaust gases are getting into the coolant, but that only works on a closed lop cooling system.
After reading here and other forums I am thinking the next step is a leak down test and listen for air escaping when listening down the oil filler tube. That MIGHT indicate head gasket(s) are gone. If no hissing there maybe that indicates possible issue with block.
The other big variable which I just don't understand since I haven't taken one apart yet is the exhaust riser. I have read that it's possible for this to rot and let water in the exhaust. If only cylinders 5 & 6 had their exhaust valve cracked open then this could make sense.. but not highly likely. I just simply don't know enough about how these work.
Also, with all plugs pulled I ran the starter for about 20-30 seconds and listened closely to the small block and the valve train for knocks and ticks. Seems like the seize due to water in the cylinders did not bend anything from my initial investigation. I'm open to any suggestions on other tests to be sure that seizure itself did not cause any problems.
Recommendations on how to figure out how water got in these two cylinders??
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