Now this sucks!!! Bad news for my OMC 3.8L V6 :(

[Watercanuck]

Well for those of you that were reading about the problems I was having things just got worse...<br /><br />Where I had water in my gas and carbs we thought it was causing my boat to studder and stall at 4000 RPMs... <br /><br />Today the marine mechanic drained the water out of the tank, removed and cleaned the carbs and did an oil change. Although the boat runs better there is still a power loss and the reason for this is one of the cylinders have very low compression. The mechanic said the compression should be around 150 but on cylinder #1 the compression is only 40 whereas the other 5 are at 150.<br /><br />The mechanic said he doesnt know if the piston is stuck or if the valves are stuck. Another odd thing is on that cylinder that has low compression the spark plug wire jumps in voltage with a voltage meeter plugged into it.<br /><br />Here is where I need your expert advice folks.<br /><br />1) The engine runs VERY smooth<br />2) There is NO knocking whatsoever<br />3) The boat excels very well and plans in a matter of seconds.<br /><br />I'm thinking its valves being stuck not piston because I think if it was a stuck piston or a broken piston rod I would hear knocking right?<br /><br />Is there any kind of fuel or oil addative you would recommend that may help free a stuck valve or piston?<br /><br />I can't put $4000 into the motor because the boat honestly isn't worth it.<br /><br />Suggestions?<br /><br />John Marshe<br />1984 20' Tempest Cuddy w/ 1984 OMC Sterndrive 3.8L V6

 

[jeff13601]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

I will tell you something that an elderly mechanic told me years ago allthough I will probably get chastised for it. Pull of your flame arrestor and start your boat and let it idle. Take a can of wd 40 and spray it into the throat of the carb until the motor bogs down and let the motor catch back up and do it over a few more times. He stated that this would help free up sticky valves. I have done it myself thinking I might have a valve stuck but do not know whether it helped or not but the engine straightened up. Im ready to take my beating now, lol. If he would have put a shot of oil in the bad cylinder and done another test he could have probably found out what the problem was

 

[DHPMARINE]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

John,I can't give anymore than my thoughts,so here goes.<br />If the pistons or valves were stuck you would have a very noisy engine,or it would not spin at all.<br />Low compreion in one cylinder could be bad rings.a burned valve,or bad head gasket.<br />The motor maybe 'smooth' because of how it is mounted in the boat.<br />Using insulated pliers,pull one plug wire off the motor while its running.If you find one cylinder not supplying much power,It's where the problem lies.<br /><br />DHP

 

[Watercanuck]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

Jeff13601 - I emailed your suggestion to the marine mechanic to see what he thinks about shooting the WD40 into the carb or a shot of oil into the cylinder. Thanks for the suggestion.<br /><br />DHPMARINE - I agree with you about the stuck piston. These motors are not so different in respect to a car's engine as far as the pistons go and how they work. If the piston was stuck then most times the piston rod would snap and you would hit a loud tapping or if the piston rod didn't snap it would/could jam the camshaft and no pistons would move. There is NO odd noise coming from the engine and in fact when I said smooth I meant that when you cruise in this boat you can hardly even hear the engine at all let alone any knocking or tapping. There is no leaks from under the heads so I'm not sure about a bad head gasket but I never even thought about the bad piston rings. Don't know what you mean by the burnt valves however. Do you mean carbon buildup on the valves? Never heard of a valve being "burnt" before.<br /><br />I think you can get a type of oil additive that helps seal leaking piston rings and other stuff that helps clean valves. Do you recommend any of these products?<br /><br />Anyone else have any comments/suggestions?<br /><br />Thanks in advance!<br /><br />John Marshe<br />1984 20' Tempest Cuddy w/ 1984 OMC Sterndrive 3.8L V6

 

[jeff13601]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

Before you start just guessing and hoping, do a wet test on the weak cylinder and find out for sure what is happening. If the rings are bad on that cylinder it isnt going to cost 4000.00 to fix it, but first you need to find out if it is a bad ring or valve problem

 

[Wotknot]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

Marvel Mystery Oil claims to do it. Have heard some of the oldtimers swear by it. I personally have never tried it though.

 

[Limited-Time]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

One cylinder down on compression, most likely valves or head gasket. If you buy a compression tester (not to expensive) you can verify for yourself the problem. (There is a link posted by Don S that details the procedure and how to interpret the results.) If you can’t find the link let me know and I will locate it for you. Or you can use a vaccume tester to diagnose the problem, again there is a link available describing how to interpret the gage readings. Then decide where to go from there. Good Luck.

 

[husaburg560]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

To determine if it's your piston rings or valves. Squirt some motor oil in to the sparkplug hole and turn the engine over a couple of times. Screw in your compression gauge and crank engine over. If the reading goes up, theres a problem with your rings. If it stays the same it's most likely with the valves.

 

[Watercanuck]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

Thanks guys for all your knowledge!<br />I just left a message with my marina to have the mechanic do as you suggested.<br /><br />A friend of mine successed that I add 2 cups of kerosene to my oil which was just changed yesterday and run the engine for 5 minutes then drain the oil and put new oil in along with 1qt of tranny fluid. Run for 10 hours then do another oil change with new oil again. He said the kerosene will help clear out a lot of junk in the engine and that tranny fluid is a good cleaner as well.<br /><br />Have any of you ever heard of this?<br /><br />Also if it is a stuck valve how do you get it unstuck? Or if its a worn piston ring do you think an additive will help seal any scratches in the cylinder walls? If not are we talking about pulling the piston out and replacing the rings? (huge expense)

 

[Alexo1us]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

I have used the kerosine trick to clean up my car motor when I leave it to long between oil changes works pretty good. just be sure not to leave it running too long.<br />You really need to do a wet test as suggested. if anything was stuck valves or piston you would here some sort of noise. if it was the piston I would think there would be no compression could be a ring on the piston stuck or broken if it were a valve stuck I would think you should here some valve noise. in my limited experience I have found most ring type problems are not limited to one cylinder but are more of a sign of old age. since it appears to be in one and not the others If the wet test still shows the same compression I would pull the head since you say there is no valve noise. my thought it is a head gasket, this would produce this problem in most cases. but if the wet test is the same you are going to need to pull the head and get a look. Check for damage to the cylinder wall (broken ring) or places where it appears to have gases blowing by the head gasket seals.<br />BTW if the the guy who did the compression test is worth anythng then he should have already put the oil in to see if it makes a difference which may be why he told you ether stuck piston (Rings)<br />or valve.<br />Good luck hope you get it worked out.

 

[Alexo1us]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

While I was looking at other post I found this posted by another forum member<br /> http://www.boatfix.com/merc/Bullet/97/97_25.pdf <br />this will give you a good test. Before you have to pull her apart.

 

[jeff13601]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

I am glad alex said that about your mechanic so I didnt have to. Buy a compression tester, put about one ounce of oil in the bad cylinder and turn it over once. Screw in your tester and turn the motor over four revolutions and read what it says. Might be worth the investment. You say it runs good so maybe a mistake was made

 

[Silvertip]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

Marvel Mystery Oil or Rislone are excellect oil additives (actually Rislone is a replacement for one quart of engine oil). Its an extremely high detergency 5 weight oil that works wonders on stuck rings and valves. Obviously the cylinder with the low compression is the problem. I doubt there is a stuck valve. A valve stuck open creates valve lash which creates noise and possible piston-to-valve contact. Since you have no noise, its not stuck open. A valve stuck closed would cause bent push rods or a collapsed lifter which causes valve lash and hence more noise. Since the remaining cylinders are perfect, you may have a worn cam lobe. That can be measured without disassembling the engine. Remove the valve cover and carefully measure lift on the push rod ends of the rocker arms on a good cylinder and then measure lift on the bad cylinder. If they are the same, the cam is ok. If not, cam and lifter replacement are required. Pistons can't stick on a running engine but rings can stick in their grooves which prevents a good seal. This however would be highly unlikely on just one cylinder unless that cylinder injested some moisture (like from a leaky head gasket or cracked cylinder head).

 

[rodbolt]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

wow<br /> yall are making way to much out of this<br /> at 40 psi you have a mechanical problem.<br /> usually it will be a bent valve.<br /> a snapped rod or a stuck piston would give a zero reading. as will a piston with a hole in it. either way the head comes off. a better test that the "wet" test is a leakdown test. bad rings wont give 40 psi. you have a leak someplace and its not past the rings. rings worn that bad will push oil into the combustion chamber as well as out of the engine vent tube. my bet is on a bent valve. a leak down test will tell you which valve. or if it is a holed piston it will tell you that as well. a cheap test is to remove the rocker arms on the affected cyl and attach an air hose to the spark plug hole and hit it with 100 psi or so. then listen for where the air is escaping. it will come out of the intake,exhaust or the valve cover vent. that will tell ya what is wrong but the head will still come off. try a leak down test or the air pressure test. a cam rounded off or a broken rocker will still normally get 80-90 psi. I suspect either a pulled intake or a stuck exhaust valve. but if your mechanic actually suggested a stuck piston I would also reccomend finding a mechanic that is more familiar with how your engine actually works.

 

[KaGee]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

All this is kinda mute anyway... the dude has his boat in a shop somewhere. <br /><br />Personally if my mechanic needs my advice to fix my problem... <br /><br />

 

[Watercanuck]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

You guys amaze me at how much knowledge you have!!!<br /><br />Thank you so much for all your advice/thoughts/comments. <br /><br />Seems the mechanic(s) at the marina had to go to a boat show the marina is entered into so I'm guessing they wont get to these suggestions until next week. In the meantime I'll just drive the boat on 5 cylinders and maybe it will clear itself over the weekend.

 

[Watercanuck]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

KaGee, my mechanic doesnt need my advice. When he said he doesn't know what the problem is with the one cylinder he would need to investigate further. That may have included the suggestions above but he didnt ask me to ask around. I took that on myself to see what other people think. Second opinions are always nice to have...

 

[Phantom17]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

You really want to run around on 5 of 6 cylinders? I personally wouldn't be doing that if I were you. Might as well stop before you possibly create a bigger problem. Good luck.

 

[jeff13601]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

John, I am wondering if possibly the mech made a mistake while doing the test. I would think that you would feel the weak cylinder. You say it runs great and planes quickly. Pull the plug wire while it is idling and see if you notice the diff in the sound of the motor. You may be worrying over nothing. Were you there when he did the test and if so did he double check it?

 

[Limited-Time]

Re: Now this sucks!!! Bad news for my OMC 3.8L V6

If it’s a head gasket you can "burn" the head and block (trashing both) by running the engine. If it’s a bad valve or camshaft, additional damage will also occur. Best bet let it sit until ya get it fixed.