Cruiser’s Valve Cover Mod

Most early and even later Renix 4.0s could be bothered by excessive oil in the air cleaner box.

A fix from my old days as Service Manager at a Jeep dealership follows. Information was provided to me from a buddy at JeepTech during those days. I don’t believe it ever came out in a Technical Service Bulletin.

Remove the valve cover and turn it over. Next, remove the fluted tubes that are now facing you by removing three screws on each.

Valve cover flute

Chop 1 inch off each of them. Then, drill a half inch hole as shown in the photo. The flat side of the flute that’s closest to the edge of the valve cover. valve cover flutes (2)


Clean and de-burr/sand all rough edges nicely, clean with solvent, and reinstall. Don’t be concerned about the chintzy gaskets that will probably crumble into oblivion when you remove the fluted tubes. They can go back together without gaskets.

Here’s a handy video from my friend Brendan showing more detail.

Revised 09-12-16

66 thoughts on “Cruiser’s Valve Cover Mod”

    1. Possibly. Although the stamped steel valve cover I ran across in my used parts collection the other day seemed to have long flutes on it.

      Finned aluminum is way sexier IMHO.

  1. my gaskets inside the flutes had metal gaskets inbetween that guard the triangle holes, can i toss these?

  2. Wait I thought the metal things were the gaskets? (I left them out) So install the metal shields back but only throw away the cracked black plastic things?

    Because I just did the head gasket, valve cover gasket, throttle body gasket, thermostat and gasket, oil pan gasket, trans fluid filter and gasket, manifold gasket, valve stem seals, all new vacuum lines (except the one from the MAP to the throttle body), new spark plugs and cables, new ignition coil, new EGR valve, new MAP sensor, new exhaust manifold… and now it cranks but will not turn over.

    – I haven’t replaced the o2 sensor air temp sensor.

    -The metal egr valve tube was slightly too long for the new exhaust manifold so I bent it a little and wasn’t able to screw and tight so I sealed it with exhaust sealer.

    Before that big project it was dying at stops and I had already replaced the TPS, IAC Valve, CPS, Battery cables, exhaust pipes.

          1. Crusier, ive been working on a valve cover 2nd infact its a 96 GC and there are holes already in the stands that are against the valve cover so I shouldn’t need to drill or was this a correction in the redesign with grommet ccv?

          2. Ok thank you for the reply, ive been chasing a possible oil consumption issue, which I don’t actually have, it is a later model 4.0 stroked and have about 10k on it now but with the factory sheetmetal cover I was filling up the oil/air separator and with the aluminum with fluted stand tubes I barely get residual in the can so I have been farting around and the 96GC with grommets as the sheetmetal had has worked great, boy with a 5/8 newcomer spacer the upgraded valvesprings are close to the sides lol.

  3. Curious, I’m dealing with a 95 4.0 in the wife’s dog mobile. This engine went through 3qts of oil in 2k miles. I just went to a colder spark plug due to pinging when I noticed no oil on the stick :/ The plugs looked great. No oil in the air box as there shouldn’t be due to the way it circulates. No blow by at all. With engine running oil cap off nothing coming out at all. I did not do a leak down but everything looks too good and I’m thinking the dam back valve cover CCV vent is sucking raw oil into the intake manifold and drinking the oil even though the plugs look great with the exception of the rear plug with had some white build up and crap on it. I thought it due to being in the cold hole and not gapped properly? No sign of oil in the exhaust. No smoking when coming down hill on compression. No smoke after sitting and startup so guides are good. And of course no leaks. Any feed back on this greatly appreciated and happy to donate to your cause and you have done an amazing job putting this info out there. I also have a 2000 TJ and any suggestion’s on which tips and tricks to do to both of these would be wonderful as well..

    1. Make sure the CCV tubes are not compromised at all and that they fit snugly into their grommets.

      Remove the rear tube and make sure there is an orifice restrictor in it and that the tube is not jammed way down through the grommet.

      1. Everything is in great shape. The rear grommet is restricted but there is no type of diaphragm in it. Just a very small orifice. I am thinking about putting a very small brass intake port fitting to restrict it more. I was actually going to do it today.
        I can see that the rear tube should NOT be bottomed out against the bottom of the grommet maybe, as that would create a possible suction to pull the oil back into the intake?
        Thank you for your feedback.

  4. 1st off awesome website and thank you for all the hard work and maintenance on it with keeping it up to date.
    My question is as follows the two vents on my valve cover are leaking oil when the motor warm up and it is in turn running down the back of the motor and making a mess replaced with fel-pro gaskets. will this mod help that situation and while i have it apart can i replace the vents or have they gone the way of the dodo? thank you for all you do from Colorado!!

      1. I have the same condition as Shannon Dee; 89 Ltd. with 46K miles using about 1 quart/500 miles with no sign of where it’s going. No leaks, smoke etc. Along with tips 1-5, I just did #25 and there is no restrictor in the rear hose. any idea on the part # for the restrictor? Rock Auto PN 46005 is for the hose and doesn’t show a restrictor either.

          1. Thanks. Great information here, I’m working through your Tips.
            Compression check is next, any tendency for these (I6) engines to have a stuck oil ring?

  5. So it was stated earlier that the later model stamped steel might provide a cure for this as well with the exception of the longer flutes as it already had the 1/2″ hole on the back.
    I just pulled a VC off my ’93 parts XJ (finned aluminum with more secure CCV ports) and noticed that it had the longer flutes but also has the holes pre done.
    Would it be necessary to cut off the 1″ or would the holes alone be enough to solve this problem?

      1. Would you cut the flutes if there were a 5/8 spacer for adjustable rockers , maybe a 1/4 versus the whole inch?

  6. I’m going to do this ASAP. The source of my worst oil leak turned out to be my airbox (88XJ), dripping from the underside. The amount of oil was significant, is there anything else I should do preemptively or does this cure even the worst oil infiltration?

    1. Make sure the vacuum line from the rear of the valve cover is clear.
      Actually, if you look at my vacuum harnesses tip, you will see the part number for that harness with new grommet and orifice. Under $10. I’d just do it.

  7. Thanks for the website Cruiser. Just picked up my first MJ and this is the first tip Im working on because I have the 2.5 liter with the stupid plastic valve cover and there’s an oil slick wherever I park. Got an aluminim VC and thought I would do this while I have it off.
    My question pertains to the 1/2″ hole you drill after cutting the 1″ off the tubes. In your picture and your instructions you drilled the hole on the side of the tower closest to the VC. In the video he drills them on the side of the tower facing the firewall. Which is correct or does it matter?

  8. Question on this, my 89 has a PCV valve on the back, which is apparently a mod a previous owner did since this system should be CCV right? While I’m doing this mod should I order that grommet and tube kit (Dorman 46005) and switch it back to stock or continue using the PCV in the back vent?

      1. Thanks! I bought all three vacuum hose assemblies. I took my valve cover off to replace the gasket last week and I was going to do this mod at the same time, but ran out of time. I did notice while I had it off that the metal plate thing on the back flute is missing, is that going to be an issue swapping everything back to stock?

  9. I am getting ready to do this mod and your instructions say drill the hole closest to the side of the valve cover and the video says on the side pointing toward the firewall??

  10. Your buddy did it wrong he left an inch of material and drilled the hole on the side closest to the firewall. Lol

  11. I did the mod and now I’m running horribly. I think I drilled it wrong. Is there somewhere I can get replacement tubes?

  12. He drilled the side not the end (as pictured in this write up), that faces the closest side of the valve cover.

    As per the write up photo, after reinstalling the tubes the drilled hole would almost be touching the side of the valve cover. Which was correct method as pictured.

    1. I don’t think it really matters. The problem was the tubes were too long and sucking up oil like a vacuum cleaner nozzle.

  13. Hey thanks for all this good information but I have a 88 Cherokee 4.0 and I replaced the whole vacuum harness and it helped get rid of some of the oil in the airbox but when I disconnect the ccv tubes and run the engine with no oil cap it has vapors coming out of the engine is that normal or is it blow by thanks

  14. has anyone a parts list of what they use to to install a metal elbow on the valve cover (aluminum cover) to replace the silly leaky rubber elbow that goes to the aircleaner via the half inch dia. hard plastic tube? the rubber elbow is junky and leaky, and I worry dust or water from off roading may enter thru there. I installed a new rubber elbow which I could only find by purchasing the whole hard plastic hose assembly, and it is a poor fit (hencho in red china!) and has shrunken and gotten looser in short order. they wont last long due to oil and heat, simply a horrible design.

    I am thinking metal conduit or plumbing parts, with a Viton gasket, held by a big nut on the inside of the cover is way to go.
    What have you all used?

  15. Cruiser, I recently did this mod but the gaskets that are between these fluted tubes and the valve cover disintegrated. I can’t seem to find the part or what it would be called. Any recommendations?

  16. Hi Cruiser54, I’m in the process of you valve cover modification. Are my eyes deceiving me or is the hole you have drilled depicted, larger than 1/2 inch and more than 1/2 inch below the top. I watched the video and I’ve already read the posts regarding how in the video the holes were drilled into the sides and it really won’t matter. I’m just really curious if those holes in your pics are larger than 1/2 inch.

  17. If I’m not mistaken the video does not show the 1/2 in hole being drilled in the correct place, or at least in comparison to the picture you have posted.

  18. Could oil coming out of the rear suction tube or front vent tube onto the valve cover be a problem that is resolved by this mod, I also have oil in the air box and have been reading up on this topic a bit. Trying to avoid replacing my vacuum harness front and rear since my suction tube isnt clogged nor is the rubber worn

  19. could a catch can also work or is this a better method of fixing the problem. I have it leaking out the top of the valve cover and into the airbox, was considering buying a new valve cover gasket and vacuum harnesses to do this mod if its a better solution as well as fix the fill plug.

  20. Hello cruiser. I did this mod, but still have a little oil seeping around the rear grommet. I was wondering if I still need to shorten the flute some more? Or if that is normal, it will always seep a little bit? I did exactly as the directions stated.

      1. Thank you for the reply. A mechanic unfamiliar with jeeps told me it’s blow by and my engine is worn out. I of course thought oh crap.

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