Blowing Oil...UPDATED

[bratay]

I have a 3.7 (4 cylinder) Mercruiser which blows oil out of the breather cap when more than half throttle, compression a little low in # 3 & timing mark off the scale. Is it likely for the timing to be the cause of all of this, or should I just pull the engine ??<br />The compression is 90, no oil in coolant, no PVC valve, engine runs great unless I time it according to the marks and a little hard starting unless dialed in just right

 

[mrnobody]

Re: Blowing Oil...UPDATED

it seems to me that you have a large amount of backpressure. sounds to me like you have a<br />bad ring in #3. allowing compression to excape past the ring.<br />the only repair i know is to re ring this motor.<br />but this is the opinion of an auto mechanic<br />could change for a marine application.<br />louis

 

[Fouled Plug]

Re: Blowing Oil...UPDATED

What are your compression readings? Any sign of oil in the coolant?

 

[bertherr]

Re: Blowing Oil...UPDATED

The oil coming out of the breather is probably from blow by from your #3 cylinder. I think the timing mark being off the scale is from the outer pully spinning on the inner hub of your harmonic balancer. I had this happen to me and the pulley eventually flew apart. Bert.

 

[petryshyn]

Re: Blowing Oil...UPDATED

Hi ho<br /><br />>as Fouled Plug says, what the compression?<br />>does the engine perform well?<br />>does the engine have a PCV valve?

 

[ODDD1]

Re: Blowing Oil...UPDATED

Bratay, you probably have a damaged #3 piston, broken ring lands/rings causing compression pressure to enter the oil pan, and out the breather....there is no balancer to slip, the 'rotor' on front of the engine with the timing marks on it is a one piece unit....when you get this thing fixed, retime the engine ar 8* degrees....was a service bulletin to drop those extra 2* for piston durability......

 

[petryshyn]

Re: Blowing Oil...UPDATED

Compression is 90 on what? all cylinders or only #3?<br /><br />>can someone explain the crankcase venting system on this engine to me? It must have a PCV valve or a fixed orfice vent to intake, not? Can't beleive it would use just a road draft tube.........LOL<br /><br />

 

[bratay]

Re: Blowing Oil...UPDATED

Since # 3 is the cylinder that is low, yes that is the one that would be reading 90 I do not recall a PVC valve but I will double check when I go up there later this week

 

[petryshyn]

Re: Blowing Oil...UPDATED

what's the other cylinders reading?.... why so secretive....is this a test?....are we on camera...LOL<br />90psi on 1 cyl. doesn't give us the whole story. If the others are around 100, it may just mean your gauge or methods are skewing the results. if you have a pvc system and the valve or hose are restricted, crankcase pressure is natural. Thats why performance is another clue. if it performs well and idles well, i'd be re-evaluating. you could have low comp in 1 cyl due to valve issues which would be unrelated to your blowby. <br /><br />we're not nosey, but more info always helps...

 

[bratay]

Re: Blowing Oil...UPDATED

The other 3 cylinders are around 110, I have not made it up to the boat yet this week,I do not recall a PVC valve and I believe that is why I changed the solid oil filler cap to a breather cap. The boat preforms great you have to ease into the throttle, but once you do it runs along good and it idles well as long as I do not try to time according to the marks if you need a more precise comp. reading I'll be glad to take another one, the valve issue is what I'm hoping for or maybe the valve staying open a little late or opening a little to soon due to the timing issue. THANKS

 

[petryshyn]

Re: Blowing Oil...UPDATED

somethings weird here.....you say the filler cap wasn't vented before...If the rocker cover wasn't designed for a vented cap(no baffle) the loss of oil through the cap could be normal. There has to be a crankcase vent system of some sort, on the engine!! Have to determine what you have, and check its performance. Maybe its the low cylinder causing grief, but I think there is more here than meets the eye......

 

[bratay]

Re: Blowing Oil...UPDATED

I could be wrong about the PVC valve maybe I added the vented breather cap to ensure the venting of the crankcase. I will not be able to get up there til Mon. or Tue. waiting on part for furnace I need to take up there. I'll get back to you then. Thanks for your time.