3.0 Merc leakdown questions

[Sabe]

I did a quick leakdown on my 2000 3.0 Merc today, I noticed there isn't any kind of PCV system on these engines but its all vented out. I took off the oil fill cap and noticed a lot of blowby coming out of the filler hole. Anyways, this lead me to a leakdown test and here are my results

1st cylinder-9% 2nd-12% 3rd-17% 4th-12%

Do you all think number three is anything to worry about? Thanks ahead of time!

 

[JustJason]

Re: 3.0 Merc leakdown questions

Eagh... it all depends on the gauge that you used, how much psi you pumped in it, and the exact location of the piston in the cylinder. 3 obviously stands out, but what are your actual compression numbers?
You will feel some "wind" comming out of the breather hole, that's just normal crankcase pulses.
Are you having any problems with the boat that led you to do the test?

 

[Sabe]

Re: 3.0 Merc leakdown questions

I havent checked just compression numbers. The reason I checked was because I popped the top off the oil fill and it was puffing pretty strong. I havent had any problems at all out of the boat. I was just curious with the blowby.

 

[fcawth]

Re: 3.0 Merc leakdown questions

I don't think what you are feeling is blowby. There are only 4 cyls. and they are pretty big so I think you just feel the air puffing in and out both ways. Mine does the same thing (3.0 volvo but same block). I too was alarmed when I first noticed it.

Mine does have a PCV valve along with the vent to the carb like yours has, although I don't think the PCV valve really does much with that big hole on the other side of the valve cover... Anyway I just put my finger on the vent hose and the PCV valve pulled vacuum on the crankcase (it sucked on my finger), so I convinced myself that it wasn't blowby.

Hope this helps..

Fred