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Mercruiser 3.0 blow by/ turn engine manually

C

Cam_92gt

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Hey everyone, I have a 2001 bay liner with a mercruiser 3.0. Engine is a remanufactured motor installed in 2017. On my 2nd trip this year I noticed oil in the bilge being pushed out through the dipstick. Seems like slot of blow by coming from oil cap as well. Compression test reads 165psi on all cylinders cold. I haven’t done a leak down test because I don’t know how to spin the motor manually to get piston to TDC on compression stroke. The crank pulley is blocked by the motor mount and the water pump and alternator pulleys do not have enough grip with the belt to turn the engine. Is my only option to try and bump it to the correct spot with the starter or is there another way? I’m replacing the pcv valve and hose with something bigger to try and relive the pressure and stop oil leak, but I’m worried it won’t be enough and I’d like to know the internal condition of my motor. Any advice is appreciated.
 
I usually connect a remote start switch to the engine so I can "bump it" while I'm at the engine instead of @ the helm. Connect the remote start switch between +12 and the coil ( small terminal (non grounded one) of the solenoid)
 
If il is coming out of dipstick tube I would first confirm oil level with engine off. If way over level then either too much oil or water in engine.

If blow by is heavy and the oil level is ok then I would suspect a possible oil control ring break. That is the bottom ring of then three on the piston.

pull the plugs and see what they look like. If oil ring is broken one would look really black and oil soaked.

Compression is controlled by valves seating properly and the two top rings on piston sealing during compression stroke.

What did you plugs look like when you did compression test?
 
Last edited:
sandkicker said:
I usually connect a remote start switch to the engine so I can "bump it" while I'm at the engine instead of @ the helm. Connect the remote start switch between +12 and the coil ( small terminal (non grounded one) of the solenoid)
Click to expand...

Connect remote jumper to Battey + and yellow with red stripe wire on either starter solenoid or slave solenoid to CRANK the engine ONLY (KEY OFF)
 
""""I’m replacing the pcv valve and hose with something bigger to try and relive the pressure and stop oil leak,"""

wont help or change your issue so dont waste your time
 
The plugs were not terrible, you could tell they haven’t been changed in a while but they were not oil soaked. I bought the boat last summer so I have no idea of the maintenance before hand. Also the oil level is within spec according to the dipstick. Did not have this issue on the first ride this spring but noticed it on the second. It was a noticeable amount of oil in the bilge. Also no water in the engine or oil. There is no smoke coming from the oil cap and no oil is blowing through the pcv vent line. Although I think the pcv valve or connected hoses were partially blocked which is why I’m replacing those items. I will be installing them today but the only time I have oil come from the dipstick is under a load so I’ll have to go to the lake to get any more updates from that. I will try to get a leak down test done this weekend.
 
Yes but not typical.

Your last reply has a lot more info. Maybe try to add all the details in a first post!!

If no excess oil and plugs look normal and only blow by then
My first thought is a bad/stuck ring.
Because there are two rings it may show good compression.
A leak down test may show a more realist result.


What is the oil pressure when running? Any idea?
 
I don’t think my gauge is very accurate, it’s on the list to be replaced with the sending unit but it reads somewhere around 25psi
 
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