Oil consumption after head rebuild merc 5.7 2002 (maxum 2500 scr)

Forbes210

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Hi All,

After I had an issue with my heads (2 of the exhaust valves got tuliped 370 hours) i had a mechanic remachine the heads and install stainless steel valves. After I picked up the boat the engine ran great but very shortly I've noticed that it consumes an oil. After doing something about 20 hours I got to conclusion that I'm burning about 1 qt every 5 hours which is a lot. I brought the boat back to the mechanic and left it with him. He called me back saying that after doing compression test it looks like one of the cylinders got lower compression (110 rest of the cylinders was fine) and thats why I'm using so much oil. He said that when engine failed originally its possible that besides head block also could get some damage. I didn't burned any oil before. I'm finding hard to believe that the engine burns 1 qt every 5 hours because one of the cylinders. I don't get any smoke while running the boat which in this oil burning ratio it should be smoking like crazy. No oil in the bilge. It smokes a little bit at the start but it goes away after a minute. Might be carburetor. I'm about to perform dry and wet compression test and just ordered leak down tester to investigate the problem. Do you have any advice as where to look? I'm thinking that maybe one of the valve seals is leaking badly and maybe instead getting inside the cylinder it gets directly into the exhaust and thats why I don't get any smoke. Not sure how to argue with the mechanic which obviously is not anxious to investigate the problem. Thanks in advance.
 

Scott Danforth

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do your own compression test. determine which cylinder is leaking, then do a leak down test. this will tell you if it is valves, rings, or what.

you can burn oil and not get any smoke. you need to be burning a lot of oil to get smoke.
 

Forbes210

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I'll try t do the compression test today. I think I'm burning a lot. 1 qt every 5 hours seams excessive but still no sign of smoke when I'm running.
 

LX Kid

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On the cylinder, with the low compression, does the spark plug show any evidence of being oily? If your cooling system, is a closed system, is there any evidence of oil in the cooling system? Is your oil "milky" as if some oil is mixing with water? Any oily residue on the exhaust outlet? Maybe there is a clue in some of these questions. All that being said a wet/dry compression reading will be a good indicator of piston ring condition but necessarily the condition of the oil control ring. If water got down on the oil control ring it could cause havoc. Most oil control rings are 3 pieces being a spring and two rings.
 

Forbes210

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Didn't check the spark plugs yet. Its a raw water cooling system. No signs of water in the oil. Its a bravo 3 so the exhaust is under water but was I was thinking to do is to remove part of the exhaust in the engine compartment and look for an oil inside the exhaust. Also I was thinking to separate cooling water from exhaust and collect the water in the bucket and try to see if I'll find any oil residue there.
 

LX Kid

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Forgot to add, make sure your PCV, (pollution control valve), in in good working order.
 

NHGuy

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There are no PCV valves in there, just open elbows. They can't be blocked either though.
If your engine rings and valves test good your machine shop may have skipped or botched the valve seal installation.
Also since the they did new valves they may have put them into bad or mis sized valve guides. So, if things test good let us know. Actually let us know either way!
 

Scott Danforth

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if your oil cooler has a leak, you can pump oil out of the engine into the coolant water stream and out into the water way.
 

Forbes210

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I'm suspecting that head guy had missed something which creates the problem. It doesn't look like its an common issue since theres no smoke and engine is running well. Any recommendations how to check if the valves seals or guides are good?

Where's oil cooler located? I'm fairly familiar with the striation of this engine and can't recall seeing anything. On the back of the engine theres power steering fluid cooler but that got nothing to do with the engine oil.
 

NHGuy

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You could put a vacuum on the combustion chamber and then put some mist or smoke around the valve stem, then operate the valves by turning the engine. Then watch the valve stem where it comes out of the guide to see if smoke gets pulled down by the vacuum. If you want or need to take it even further you could remove the intake and exhaust manifolds and seal off their ports to help keep all the vacuum working in the chamber.
 

Volphin

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You are either leaking oil somewhere or your piston rings are done. Valve seals and valve guide leakage would be a much more gradual loss, indicative of blue smoke on startup. Oil getting past the rings is more likely to be burned full time. What were your compression numbers wet and dry? Also, check along the base of the oil pressure sending unit and the intake gaskets along the front and back of the engine for seepage.
 

Forbes210

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I did the dry compression test. Didn't have enough time to do the wet test. Cylinder #1 had 125 psi all the other between 170 - 195 psi. Im not an expert as far of judging the spark plugs but all of them looked bad to me. They had something which looked like burned oil on the tread. Is it possible thats some kind of anti seize lubricant? Heres few images of the random spark plugs. All of them looked similar to me but had a build up. They were replaced when mechanic performed head job. I'm leaning more towards the fact that he missed something during the repair. I just need to get enough of the arguments to prove ti and argue with him. At this pint after spending close to 4k on the repair I'm getting really annoyed.

Volphin,

I do get smoke at the start up. It goes away after a minute. I thought it might be because of the carburetor but I might be wrong.

Next I'll perform wet compression test and leak down test. After I'll try to inspect the seals like NHguy advised.

Thanks for all the help guys!
 

Forbes210

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Forbes210

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The one on cylinder #8 was weird build up on ceramic part. Non of them had a washers but maybe its designed to be this way.
 

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Idlespeedonly

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You are burning oil. All of the light crusty looking deposits are from the oil.
 

Volphin

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Don't concern yourself with the threads on the spark plugs. It is the ceramic insulator color and condition of the electrodes that matter. You are looking for a light brown color. #8 is black... and is burning oil for sure. The others look fairly rich. FYI: The carb won't cause that smoke on startup, but it CAN dump fuel into the intake and cause sooting from an over rich condition.
 
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LX Kid

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To me 195 psi on a "dry" test is way high. Could that hight cylinder already have pumped oil in the cylinder? Really need to do a dry and wet test to be able to make conclusions about ring condition. #1 at 125 psi is really suspicious and am curious what a wet test would show! I'd get her up to operating temp, pull all the plugs and start over. This is an important test. Be sure to check your spark plugs gaps for correct gap after removing.
 
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Forbes210

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LX Kid thanks for a good hint. I think what's happening is that the valve seals or guides are leaking really badly to the point that they deliver enough oil to the cylinders which basically makes it impossible to do the dry test. Thats why also I'm getting oil on the spark plugs tread. Just did leak down test on cylinder #1 and its leaking through the intake valve. Thats why I'm getting such a high compression reading like 195 psi. Does it make sense? I guess head guy did something wrong either with valve guides or seals. Not mentioning leak on intake valve on cylinder #1.
 

Grub54891

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Seen similar issues myself in the past. When doing just the valves,compression goes up,weak rings start weeping oil as the valves are doing what they are supposed to do. You may not see the smoke from the exhaust. Every intake stroke creates a vacuum,pulling oil past the rings,burning it upon firing. It's pretty easy to blame the last person to touch the boat. Also its pretty hard to mess up a valve job when thats what ya do for a living. Unless it was a backyard mechanic that happens to have a valve grinder. As stated,wet/dry tests,leakdown tests are in order..
 

Forbes210

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The engine didn't use any oil before and after repair is using 1 qt every 5 hours so its substantial and I doubt its because the valves are sealing better now. Spark plugs looks like they are old and they were replaced together with head job. Theres an oil on spark plug treads which looks like they are getting flood with oil. All the cylinders got higher then normal compression test during dry test and wet test didn't improve the compression. After doing leak down test came out that cylinder #1 (the lowest compression) got leaking intake valve. All of those symptoms are leading to conclusion that something was missed in the head job. Most likely valve guides or valve seals. Definitely it doesn't look like typical wear and tear.
 
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