I thought I?d relay my story of trying to figure out how water was getting into the oil of my ?87 Mercruiser 130HP/3.0L ? maybe it will help other novices out there or at least provide some amusement for those of you who have a clue about such things. My boat was getting little use and had been laid up for 3 yrs. I decided it was time to sell so I got it cleaned up and ready to run. On checking the oil, I found it was too full so I drained it and sure enough ? water. I?ve always winterized the boat myself (since new) so was hoping the water came from somewhere other than a cracked block. There was nothing externally visible so I changed the oil and started it up to see what would happen. It ran fine, I kept checking the oil level and it was steady?.but then I noticed a foamy oil mix (like a milk shake) leaking into the bilge from the flywheel cover. I drained the oil again and found more water so not only do I have water getting in but I?m thinking probably a leaking main seal too.
I decided the boat?s value was probably less than the likely repair cost so if I couldn?t do it myself I would either junk it or part it out. Pouring over the online forums, it looked to me as if the most likely culprit was either a cracked block or bad head gasket. I made up my mind I could probably handle the head gasket so I dove in and started disassembly. OK, I now know I should have pressure tested first so probably this was dumb mistake #1. But I figured it would be just as quick to pull the head and if it wasn?t the gasket then I was done with the engine anyway.
Sizing up the job - I thought that since I was only going for the head gasket, I might as well leave everything else attached (manifold, carb, exhaust elbow) - reassembly would be that much faster, right? OK, this was dumb mistake #2: I got the head unbolted, braced myself and grabbed hold and quickly realized all of this stuff together was HEAVY?way too heavy. Once I started though I was afraid to stop so thankfully I managed to heft it off and put it down without hurting myself or the boat. Oh yeah, the water pouring down into the cylinders during all of this made me realize dumb mistake #3 was not draining the block before I started. I later learned that dumb mistake #4 was not keeping track of where the push rods came out so they could be placed back in the same order. I learned this after rectifying dumb mistake #5?.starting the job without having a shop manual.
After some more reading I learned the other good reason to separate the manifold and exhaust elbow from the head was that these gaskets are also potential leak points for water to get into the engine. Also that you should take the time to acid dip the manifold and elbow to get all of the crud out (I did not since they didn?t seem too bad & the engine probably has less than 1000 hrs of fresh water only use). None of the gaskets had any obvious signs of failure but it was hard to tell since separating everything tended to tear them up (no blow-outs on the head gasket either).
I found these forums very helpful on many of the details - like using a thread chaser vs. a tap to clean the bolts and holes?.and that this was extremely important in getting appropriate torque readings. I could also see there was some sort of thread sealant on the bolts but I had trouble finding any info on what type to use (although I did read you definitely want a sealant, NOT a thread locker). Even the shop manual was sketchy on this detail. The parts guy where I bought the gaskets recommended a high temp gasket sealant for the threads (the label on the can backed him up on this). I ended up using the same product to coat the manifold gasket and the exhaust elbow gaskets. I was also not sure about whether the head gasket went on dry or needed a sealant but eventually learned this went on dry (this was perplexing because the head and block definitely looked like they had some sort of sealant residue on them and the engine has never been apart).
After thoroughly cleaning all of the surfaces, my last concern about reassembly was that there was a small scratch on the head and also one on the mating surface of the block. They were very small ? about an inch long - but visible and enough to catch a fingernail. Getting these machined was definitely not in my project plan. I toyed with the idea of putting a drop of sealant on each spot but figured that would likely do more harm than good so I decided to just put it all together and keep my fingers crossed (hopefully not dumb mistake #6). I put the new gasket on, then the head and the now randomly ordered push rods. Oh yeah, I did not have a tool to compress the valve springs so I backed out the rocker bolts where I had to, counting the turns, to get enough clearance to insert the rods then tightened them back up the same amount (# 7, who?s counting?).
The rest of the reassembly was uneventful and it was finally time to fire it up. Much to my surprise and delight, it started immediately and ran great! After a minute though, I realized there was a fair amount of white smoke (steam?) billowing out of the exhaust. This really took the wind out of my sails, I was thinking either those scratches were more serious than I thought, maybe I really was supposed to use a sealant or possibly I messed up torquing the head bolts (although I was careful: going in the proper sequence and doing it in 3rd increments of the final torque value). I let it run for about 10 minutes to see if it would clear but sadly it did not. I shut it down and decided I would re-torque the head bolts the next day in a last, vain attempt to seal the head.
The next morning I fired the engine up again and waited for the white smoke to start ? but it never did! I ran it for about 20 minutes at various RPMs and it ran as smooth and clean as it ever has. I could only surmise that the coating they put on the head gasket heated and sealed when it cooled from the initial start-up. Did I accidentally do this right? I continued checking the oil: it was free of water and the level did not change. I also kept checking the flywheel cover at the spot of that initial leak and there was no dripping. There seemed to be some oil residue but it was hard to tell if it was left over from before or if there still might be seepage so I decided to add a quart of Barrs Main Seal Repair to the oil (better than the alternative if there really is an issue with the seal).
I ran the engine for about another hour and everything seems to be fine ? no smoking, no seepage. My only issue now is that boating season is over here in the Northeast so now I have to winterize it and put it away again.
I decided the boat?s value was probably less than the likely repair cost so if I couldn?t do it myself I would either junk it or part it out. Pouring over the online forums, it looked to me as if the most likely culprit was either a cracked block or bad head gasket. I made up my mind I could probably handle the head gasket so I dove in and started disassembly. OK, I now know I should have pressure tested first so probably this was dumb mistake #1. But I figured it would be just as quick to pull the head and if it wasn?t the gasket then I was done with the engine anyway.
Sizing up the job - I thought that since I was only going for the head gasket, I might as well leave everything else attached (manifold, carb, exhaust elbow) - reassembly would be that much faster, right? OK, this was dumb mistake #2: I got the head unbolted, braced myself and grabbed hold and quickly realized all of this stuff together was HEAVY?way too heavy. Once I started though I was afraid to stop so thankfully I managed to heft it off and put it down without hurting myself or the boat. Oh yeah, the water pouring down into the cylinders during all of this made me realize dumb mistake #3 was not draining the block before I started. I later learned that dumb mistake #4 was not keeping track of where the push rods came out so they could be placed back in the same order. I learned this after rectifying dumb mistake #5?.starting the job without having a shop manual.
After some more reading I learned the other good reason to separate the manifold and exhaust elbow from the head was that these gaskets are also potential leak points for water to get into the engine. Also that you should take the time to acid dip the manifold and elbow to get all of the crud out (I did not since they didn?t seem too bad & the engine probably has less than 1000 hrs of fresh water only use). None of the gaskets had any obvious signs of failure but it was hard to tell since separating everything tended to tear them up (no blow-outs on the head gasket either).
I found these forums very helpful on many of the details - like using a thread chaser vs. a tap to clean the bolts and holes?.and that this was extremely important in getting appropriate torque readings. I could also see there was some sort of thread sealant on the bolts but I had trouble finding any info on what type to use (although I did read you definitely want a sealant, NOT a thread locker). Even the shop manual was sketchy on this detail. The parts guy where I bought the gaskets recommended a high temp gasket sealant for the threads (the label on the can backed him up on this). I ended up using the same product to coat the manifold gasket and the exhaust elbow gaskets. I was also not sure about whether the head gasket went on dry or needed a sealant but eventually learned this went on dry (this was perplexing because the head and block definitely looked like they had some sort of sealant residue on them and the engine has never been apart).
After thoroughly cleaning all of the surfaces, my last concern about reassembly was that there was a small scratch on the head and also one on the mating surface of the block. They were very small ? about an inch long - but visible and enough to catch a fingernail. Getting these machined was definitely not in my project plan. I toyed with the idea of putting a drop of sealant on each spot but figured that would likely do more harm than good so I decided to just put it all together and keep my fingers crossed (hopefully not dumb mistake #6). I put the new gasket on, then the head and the now randomly ordered push rods. Oh yeah, I did not have a tool to compress the valve springs so I backed out the rocker bolts where I had to, counting the turns, to get enough clearance to insert the rods then tightened them back up the same amount (# 7, who?s counting?).
The rest of the reassembly was uneventful and it was finally time to fire it up. Much to my surprise and delight, it started immediately and ran great! After a minute though, I realized there was a fair amount of white smoke (steam?) billowing out of the exhaust. This really took the wind out of my sails, I was thinking either those scratches were more serious than I thought, maybe I really was supposed to use a sealant or possibly I messed up torquing the head bolts (although I was careful: going in the proper sequence and doing it in 3rd increments of the final torque value). I let it run for about 10 minutes to see if it would clear but sadly it did not. I shut it down and decided I would re-torque the head bolts the next day in a last, vain attempt to seal the head.
The next morning I fired the engine up again and waited for the white smoke to start ? but it never did! I ran it for about 20 minutes at various RPMs and it ran as smooth and clean as it ever has. I could only surmise that the coating they put on the head gasket heated and sealed when it cooled from the initial start-up. Did I accidentally do this right? I continued checking the oil: it was free of water and the level did not change. I also kept checking the flywheel cover at the spot of that initial leak and there was no dripping. There seemed to be some oil residue but it was hard to tell if it was left over from before or if there still might be seepage so I decided to add a quart of Barrs Main Seal Repair to the oil (better than the alternative if there really is an issue with the seal).
I ran the engine for about another hour and everything seems to be fine ? no smoking, no seepage. My only issue now is that boating season is over here in the Northeast so now I have to winterize it and put it away again.
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