blow-by or something else

[watchamakalit]

Ok I want to start with saying I have recently (last 5 years) replaced the ccv breathers and confirmed no blockage, cruiser54 modded my valve cover breathers, switched to lighter viscosity oil and my dilemma persists. I can't stop this old girl from running an oil bath air filter. Am I missing something obvious or is she just ready for an ls style catch can?

 

 

[GonzoTheGreat]

Is the little vacuum line that runs from the other port on the valve cover clean and free-flowing? That’s the one that is meant to draw blow-by to the intake. If it’s clogged, cracked, or disconnected, it can cause this. 

 

also what oil do you run? I would imagine a thinner oil would actually increase blow-by.

[AnotherOldJeepGuy]

25 minutes ago, GonzoTheGreat said:

Is the little vacuum line that runs from the other port on the valve cover clean and free-flowing? That’s the one that is meant to draw blow-by to the intake. If it’s clogged, cracked, or disconnected, it can cause this. 

 

also what oil do you run? I would imagine a thinner oil would actually increase blow-by.

Mine was fragile enough that I failed to get it off in one piece to clean, but it is still available at Napa and doesn't cost much.

https://www.napaonline.com/en/p/NOE7151365

[pizzaman09]

I added a GM style PCV to mine to help reduce the oil getting into the filter.  Do read the following posts after my install as I found I needed to reduce the PCVs effectiness some as it caused my rear main seal which needed to be replaced, to leak ever worse.

 

[watchamakalit]

Yes the rear line is clean and free flowing.  I was running 15w40 rotella, but heard it could be an issue of oil not draining back through the block fast enough cause by heavy oil weight. Last oil change I went to 10w30 and there has been little to no change. This seems to be the one oil leak I can't stop.

[AnotherOldJeepGuy]

2 hours ago, pizzaman09 said:

I added a GM style PCV to mine to help reduce the oil getting into the filter.

So my educational quota is a bit behind on this, what is essentially the difference with this part compared to the original?

[pizzaman09]

1 hour ago, AnotherOldJeepGuy said:

So my educational quota is a bit behind on this, what is essentially the difference with this part compared to the original?

It has a 1 way valve in it.  The original is just a pipe.  I'm not sure that it improves the way the crank case is ventilated, but it has stopped the air filters from getting covered in oil on both Comanches I have owned.

[AZJeff]

The 4.0 engine has what is called a "controlled crankcase ventilation system".   That means that the rear hose is sized such that an engine in "as designed" condition will suck normal amounts of crankcase vapors through that rear hose and burn them with the combustion air being drawn into the intake manifold.

 

When a 4.0 engine becomes substantially worn, this vent hose is not large enough to deal with the larger-than-normal amount of blow-by that the cylinders leak into the crankcase past the piston rings.  Once this condition exists, the crankcase now has more pressure in it than the rear vent hose can scavenge from the bottom end of the engine, and the excess vapors now seek another way out.   That way out is the front hose on the valve cover, which is normally providing INLET AIR to the crankcase.   The end result is oil vapors in the air filter and air box.

 

One can increase the size of the rear crankcase vent hose, but that also upsets the airflow mass being measured by the MAP and Throttle Position Sensor, and will result in a leaner mixture.    A little bit of extra crankcase vapors being sucked in by a larger vent hose is not seriously harmful, but a large amount will cause long-term engine damage.  (Using a PCV like "Pizzaman09" suggested helps limit the amount of crankcase gases being drawn into the manifold to some degree.)

 

The real fix, of course, is to fix the blow-by on the engine by reboring the engine for oversized pistons/rings.

[llhat]

just an FYI on the above link for the PCV valve.. it is on page 7....    thank you for sharing that info...

 

[Ωhm]

What if the orifice (2.6mm) is removed/enlarged. This would increase the draw into the manifold. I think the IAC would compensate for this additional air draw while STFT and LTFT would maintain the fuel ratio (stoichiometry). Might help.

[AnotherOldJeepGuy]

Thanks for the education @pizzaman09 and  @AZJeff!  I suspect my 230k miles has landed my Jeep somewhat out of the "as designed" condition!  I don't see the "real fix" getting done in my lifetime , I think I will monitor the filter and see if the new line I recently installed was of any benefit before going any farther.

[pizzaman09]

4 hours ago, AZJeff said:

The 4.0 engine has what is called a "controlled crankcase ventilation system".   That means that the rear hose is sized such that an engine in "as designed" condition will suck normal amounts of crankcase vapors through that rear hose and burn them with the combustion air being drawn into the intake manifold.

 

When a 4.0 engine becomes substantially worn, this vent hose is not large enough to deal with the larger-than-normal amount of blow-by that the cylinders leak into the crankcase past the piston rings.  Once this condition exists, the crankcase now has more pressure in it than the rear vent hose can scavenge from the bottom end of the engine, and the excess vapors now seek another way out.   That way out is the front hose on the valve cover, which is normally providing INLET AIR to the crankcase.   The end result is oil vapors in the air filter and air box.

 

One can increase the size of the rear crankcase vent hose, but that also upsets the airflow mass being measured by the MAP and Throttle Position Sensor, and will result in a leaner mixture.    A little bit of extra crankcase vapors being sucked in by a larger vent hose is not seriously harmful, but a large amount will cause long-term engine damage.  (Using a PCV like "Pizzaman09" suggested helps limit the amount of crankcase gases being drawn into the manifold to some degree.)

 

The real fix, of course, is to fix the blow-by on the engine by reboring the engine for oversized pistons/rings.

The controlled airflow explains why my engine had lots of blowby, it's got 270k miles on it.  Also this explains why when I added the PCV which really just restrics flow from the air filter, that my rear main seal leak got much worse.

[watchamakalit]

I only have a mild 180000 on my motor. Previous compression test show good steady non leaking compression across the board. That is part of what makes me wonder if there isn't another underlying cause I'm not seeing.

[89 MJ]

I think these AMC I6s must just have a tendency to have quite a bit of blowby. My MJ engine has less than 150k on it and has blowby, my Eagle engine has an estimated 80k on it and has some blowby, and the previous engine in my Eagle had 110k on it and tons of blow by. Oddly enough, the first two I said have good compression and neither have any oil consumption issues. 

[75sv1]

I had this issue. I replaced the RENIX VC with a HO VC. Also, used a later 96-01 CCV Tube in the rear. Also, have to update the manifold fitting for this and lengthen the Tube. I also found that cork VC gaskets leak. So, I went with the FELPRO Silicon VC gasket. The later 96-up VC, I think has the best venting system. I still like the 93-95 ZJ valve cover. Has the later style CCV Grommets.  I pick up another on last week. It was on a '99 XJ. 

[MancheKid86]

cruisers valve cover mod, 
an old jeep/chrysler service tech I know claims he found this fix back in the day

https://cruiser54.com/?p=131

[watchamakalit]

2 hours ago, MancheKid86 said:

cruisers valve cover mod, 
an old jeep/chrysler service tech I know claims he found this fix back in the day

https://cruiser54.com/?p=131

Read the original post. Cruiser mod was done long ago, with no improvement.

[75sv1]

I think I did the Cruiser mod on both a RENIX and an HO. It didn't work for me. For should I say, it worked for a while. Then the cork valve cover gasket failed. Its a balance of air sucking from the front, vs air being sucked from the rear. 

[MancheKid86]

23 hours ago, watchamakalit said:

Read the original post. Cruiser mod was done long ago, with no improvement.

yep glazed right over that part.