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The guy who did the tuning on the car after the motor was rebuilt decided it needed a bigger catch can than the OEM one. The one he installed is like 3 x bigger and vents from the cam cover to the can on the hot side, whereas I think the OEM one was on the intake side. Not sure, but I reckon the OEM one was on the intake side and vented only from the crankcase, from low down on the intake side, not from the cam cover.

While doing this he cut and sealed the pipe from the crankcase.

Two questions:

Is there any need for oil vapour to vent to a catch can from the cylinder head?

Is the sealing off of the pipe from the crankcase contributing to the difficulties in sealing the sump by pressurising it?

Yes, the crankcase needs to be vented somewhere.

I can't remember which parts vent where on the stock MX5, but do some reading on PCV, or Positive Crankcase Ventilation, and you should find plenty of information on why and where to vent.

*Deep breath*..... Ok bear with me as this will take a bit of explaining......

The SE has two crankcase vents, one on the intake side of the cam cover plumbed to the intake manifold with a PCV (to prevent positive pressure from the boosted intake charge from pressurising the crankcase) and one on the exhaust side of the cam cover running to the catch can then onto the intake pipe (pre-turbo) via a return line.
The 'low down' one on the intake side you are describing is most likely the oil return port into the sump for the factory catch-can. If he has replaced the factory catch-can with an aftermarket unit this would need to be sealed and the new catch-can drained manually.

This means that, in the factory design, only one side of the crankcase venting is cleaned via the catch-can. The intake side is vented directly to the plenum and on into the cylinders.
My understanding is this is done to 'actively vacuum' crankcase vapours when the engine is not on boost and provide a more thorough removal of the crankcase gasses.....
The downside is that you get 'contaminated' air introduced into the intake charge when not on boost.

I have replaced the factory catch-can on my SE and modified the factory pipework to suit my application.
I now have both cam-cover vents running directly to the new catch-can (PCV removed from the intake side) which is then plumbed to the intake (pre-turbo) via a return line. This return line is required by law in NSW.
What does this mean?
- All of the vented crankcase gasses are now 'cleaned'.
- The intake barb formerly used by the intake side vent pipe on the plenum is now used as a boost signal source for my gauge.
- The oil return pipe is now sealed and the can drained manually so no 'dirty' contaminated oil is returned to the engine.
- The catch-can gas return line is a closed loop to the pre-turbo intake pipe, thus the catch-can and hence the crankcase only ever sees negative pressure or vacuum. Thus I retain the 'active' gas removal from the crankcase previously done by the intake side connection.
- The oil/gunk accumulation in the catch-can can be monitored to give an early indication of problems internally in the engine. You never see this with the factory setup as the separated material is returned to the sump and not retained.

Note: If the catch-can is vent to atmosphere (ie. a filter on the top and no return line) then the crankcase gasses will not be 'actively' drawn out unless the intake side to plenum with PCV connection is retained.

I hope this isn't too confusing as I know what I'm trying to say!

I've been running this setup for nearly a year now with no problems and almost nothing accumulating in the catch-can (hopefully this means I have a good engine).

Thanks Nev. I'll try to learn how to understand all this.

Before today:


After today:





Hopefully this will help avoid this misting from the cam cover:


and will stop the crankcase being pressurised, thus avoiding the sump seal failing again.

Sorry for the apparently upside down pics. If you click on them they enlarge and rotate. No idea why.

By the way, if the bolt in the bottom pic, which is on the coolant reroute, is rusting on the outside, no doubt it'll also be rusting on the inside. Is this a problem?

Nevyn and NitroDann must surely want to comment on the pics?

davekmoore wrote:Nevyn and NitroDann must surely want to comment on the pics?

Well apart from the pictures being small and upside down it's a bit hard to see exactly what he's done.....

When you click on them they enlarge and rotate.

davekmoore wrote:When you click on them they enlarge and rotate.

Strange, they weren't rotating earlier on.....
Still a bit small to see exactly what's happening.

The additional pipe installed from the intake side of the cam cover fitting, where does that go?

Also the catch-can appears to be a vent to atmosphere type so the crankcase is only venting excess pressure rather than being actively 'scoured' as I described in my earlier post.
Still, this should not allow positive crankcase pressure to build up (and hence damage the sump gasket) unless there's a blockage in the catch-can vent (filter) outlet.

What on earth is that extra hose doing at the pcv??

Bolt shouldn't be rusting inside if your using a corrosion inhibiting coolant.


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So here's a further challenge with my not being technically minded and needing to trust others who say they know better:

Tuner said he needed oversize catch can on exhaust side and to block off the pipe from the PVC.

Engine builder says the reason his two attempts at sealing the sump failed is that the PCV pipe was previously blocked off, thus pressurising the crankcase.

Tuner has now unblocked the PCV Pand vented it to thecam cover.

All I want is for the motor to be safe and for the next attempt to seal the sump to be successful.

off topic a bit but does it have coolant in it? top radiator hose and overflow bottle don't look great in the first pic

Call me crazy.

But, the SE has a catch can from stock, correct?

if a larger can is needed for whatever reason....

Why not just plumb it exactly the same as stock, just instead of going to the OEM can, put the lines to a larger one? (using larger hoses if needed, but keeping them plumbed to the same positions)



It just seems like this has all been reinventing the wheel despite having a spare wheel already there.

All possibly true.