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

[forbes210]

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.

[mmwjr]

A quart an hour would leave a cloud behind the boat all the time.

A leaking valve seal or worn guide would typically blow oil only when accelerating and not use near that much oil.

Worn piston rings blow oil all the time but having only one cylinder low and still above 100 psi just does not account for that much oil loss.

Try laying some oil asbor mats under the engine to verify no leaks.

I am assuming you are not getting any water in the oil, correct?

May want to pull the exhaust elbows to inspect for signs of oil.

[forbes210]

No signs of water in the oil.

I'll remove the water from the bilge and lay some mats but my bilge is clean and by this time I added about 5 quarts which in case of leak oil will be all over the place.

I was thinking about removing portion of the exhaust to see if I'll find any oil.

So far I can't find any reasonable explanation since the oil consumption is significant and I don't have any smoke.

[mmwjr]

Do you trailer the boat? If so try running it on the hose at home and look for signs of oil the the exhaust water.

If kept in the water run the boat in your slip and look for an oil sheen in the water.

Possible leaking head gasket allowing oil to enter water passages, however I would think water would also get into oil if this was the case.

Were the heads checked for cracks when you had them reworked?

[forbes210]

I keep my boat in the water- no trailer.

I do get the sheen in the water but only after the start up and thought that it might be gasoline when engine running on choke. After some time sheen goes away. I might be wrong on that.

I did over 20 hours since the head repair and didn't see any sign of water in the oil.

Supposedly they did whole nine yards with the head including all new stainless steel valves etc. Not sure if I can trust the mechanic.

[mmwjr]

Well if leak was in the heads or head gasket I would expect water in the oil pan. The reason is oil is delivered to the heads under pressure through the push rods once it squirts onto the rockers it is no longer under pressure and just runs into collector passages by gravity, from there the oil is channeled into passages in the block that run back into the crankcase.

If oil is leaking into the water yet no water into oil it must be when the oil is under pressure which is only in the block. Another possible leak could be an oil cooler but Merc did not one on it standard engines. There is a PS cooler but that would only cause PS fluid to leak.

So I guess I am thinking a crack in the block between a oil passage into a water passage. Not sure how to prove that nor do I think I was caused by the same issue that damaged the heads. Was the block drained and back filled with antifreeze last winter?

[forbes210]

The engine block was winterized by running antifreeze through it.

Is there any way to determine if the block is cracked? The engine runs fine besides oil consumption. I would like to take care of it but replacing an engine at this point sounds excessive. Is it possible that the possible oil which I see in the water comes from the exhaust?

[mmwjr]

pull the spark plugs and see if any are oil fouled

[forbes210]

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 this some kind of anti seize lubricant or simply oil getting through the treads? Here's few images of the random spark plugs. All of them looked similar to me and had a build up. They were replaced when mechanic performed head job (30 hours ago). 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 point after spending close to 4k on the repair I'm getting really annoyed. 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. Not sure how to check valve guides and seals.

[forbes210]

Spurk plug #8 had a weird black deposit on ceramic part of the spark plug. I was wondering how it could happen.

[mmwjr]

Which of these plugs was from cylinder 1 that had the lower compression?

Most look like the engine is running lean, white.

What color is the smoke at start up? Blue is oil, black is rich gas, and white is water.

[forbes210]

Mike, I did the leak down test yesterday. Cyl #1 had a leaking intake valve and that's perfect explanation why compression on this cylinder was lower. Compression on all the other cylinders was extremely high which made me thinking. I believe that either valve guides or seals are leaking oil to the point that It cumulates inside inside the combustion chamber and seals the rings. Basically it's the same if I'll be doing wet test and that's why those readings are high for this engine. That also explains oil on the spark plugs tread. Does it make sense?

[mmwjr]

Oil leaking down the valve stems will result in the plugs getting oil soaked for the portion that is inside the combustion chamber. Also yes this will cause the compression to be higher.

Been thinking those plugs look strange, white electrodes as is running lean but gray else where. They look as if they have lots of hours but are suspose to be new but I guess oil buring will cause that.

With that said I still find it hard to believe that 1 quart would leak out in 5 hours through these means additionally you stated no blue smoke when running and no oil in the bilge.

Did the mechanic do all the work? remove/install heads?

Is this guy a boat mechanic, merc certified?

[forbes210]

Mechanic which removed the head is marine mechanic not sure if certified by mercruiser. He remove the heads and gave them to other head guy who machine the heads and installed new valves. It looks like a head guy dropped the ball. I do get white/blue smoke at the start up. I thought that carburetor is responsible for that but I might be wrong about it and it might be caused by oil. No smoke during driving. Spark plugs got less then 30 hours on them and they were installed new when doing heads. Its painfull since the guy is 47 nm away from my home port.

[mmwjr]

So the marine mechanic pick the head guy and also reinstalled the heads, correct? And now does not want to standby his work, verify the issue is not due to his work?

[forbes210]

Mike, I feel the same way about it. He should be responsible for entire job. Just wanted to make sure that I got enough good arguments to show him where the problem is and don't get send back with some silly explanation from him. I called him yesterday and he will speak with the head guy on monday. I'm planning to drop of the boat with him on tuesday.

[mmwjr]

Hopefully they come to a solution that satisfies you. Best of luck.

[forbes210]

Thank you! Will keep you posted.