1995 3000GT: Homemade Crankcase Breather Hose Catch Can

• Why Do I Want To Do This?

  • A Breather Hose Catch Can is used to keep oil from entering the intake via the Crankcase Breather Hose. The vacuum in the intake is used to ventilate the crankcase (through the rear valve cover in our engines). When the pressure in the crankcase is higher than in the intake, air (and anything that happens to be floating around in the air, such as oil droplets) is sucked into the intake just before the throttle body (or before the rear turbocharger on turbo 3/Ss). Other conditions can also lead to larger quantities of oil being sucked in to the intake, but those conditions usually involve some kind of engine malfunction or user error.
  • Since I had some issues with carbon build-up in my plenum and cylinders and I do a lot of high-RPM braking/cruising (results in high intake vacuum), I wanted to be sure I didn't have any substantial quantity of oil being drawn into the intake via the breather hose. I probably don't need it, but for my own peace of mind and the minimal cost to create a catch can, I decided to put one in. It works by having the input hose (from crankcase) in the can close to the bottom and the output hose (to intake) near the top of the can. Air still flows through the can, but gravity will trap any heavy particles/liquids in the can unless there is extreme suction on the intake side. Technically, you don't need to route the output of the can back to the intake - you can just put some kind of breather filter on it and seal off the intake connection. AFAIK, the only reason to route the breather hose back to the intake is for emissions reasons.




• How Long Will It Take Me To Do This?

  • Once you have the parts, it'll probably take about an hour (maybe two).




• Anything I Should Do Prior To Attempting This Procedure?

  • Nope.




• What Mitsubishi Parts Will I Need?

  • None.




• What Other Parts Will I Need?

  • (1) Plastic jar with lid (I used a Skippy peanut butter jar)
  • (4) Feet of 3/8" ID sturdy plastic tubing
  • (2) 3/8" brass flared pipe couplers
  • (1) Tube of Silicone Sealant
  • (1) Tube of Super Glue
  • (2) [Optional] 5/8" Hose clamps
  • (1) Set of hardware, nuts, and bolts for mounting




• Erik's Review

  • After having the CC on for about 9 months (about 4000 miles) I had a few drops (maybe .5 cc) of oil in the can and a light coating of oil in the hose that connects to the crankcase. Thus my conclusion that I probably don't *need* one, but it doesn't hurt.
  • Note that this experience was on my old FWD (NA) 3000GT. Increased blow-by in turbocharged cars can generate higher crankcase pressures and more oil being blown back into the intake tract. Further complicating this is the fact that the exit for the breather hose on the turbo cars dumps right before the inlet for the rear compressor. Thus any oil from this hose goes straight into the impeller blades of the rear turbocharger, which is undesirable. I forked over the cash for an aluminum catch can for my VR-4 and it does collect a little oil (1cc every 3000-4000mi).
  • Also, I only recommend using this kind of catch can on the rear valve cover breather hose. I would not recommend using this style catch can on the PCV hose that runs from the front valve cover to the intake plenum. The reason for this is that the homemade catch can I show here is sealed reasonably well, but I'm not sure I would trust it for manifold vacuum or turbocharged boost (TT cars only). The rear breather hose never sees large vacuum and should never see boost, so a catch can on this line doesn't need to be super-heavy-duty. If you want to put a catch can on the [front valve cover] PCV hose, I'd recommend a pre-made catch can like the ones made by Cusco or GReddy.

The Procedure

Drill 2 holes in the lid of the catch can through which to feed the brass pipe fittings. Feed the pipe couplers through the bottom of the lid and anchor in place with Super Glue. Seal area around the pipe couplers with silicone and allow to dry. Cut a section of the plastic piping long enough to extend to the bottom of the jar and attach it to one of the pipe couplers on the underside of the lid. This will be the side that connects to the crankcase. Cut a section of the plastic piping about 2" long and attach it the other pipe coupler on the underside of the lid. This will be the side that connects to the intake. Attach mounting hardware to the jar lid and seal any holes you drilled. Screw on the lid of the jar (you can add some silicone to the threads if it doesn't seal completely. Cut one section of hose long enough to run from the catch can location to the crankcase nipple and one section of hose long enough to run from the catch can location to the intake nipple. Attach the hoses to the pipe couplers attached to the top of the catch can. Test that the catch can is airtight by blowing in one hose with the other hose plugged. If you can blow air into the can, it's not sealed properly. Mount the catch can in your engine bay. Connect the hoses to the intake and crankcase nipples. Use hose clamps on the intake and crankcase nipples if desired.