DIY Oil Cap Breather

Ok, so this is very straight forward and easy to do. Instead of paying money I didn’t have I chose to make my own oil breather cap to help vent crankcase pressure.

Supplies/Tools:

Drill and drill bit set
Oil cap
Apoxy or JB weld
Breather filter
PCV Valve
(and some paint in my case)

So I got start by finding center on the cap and drilling a small pilot hole first.

Then, work your way up to the size hole you need to tightly thread the pcv valve into the cap. Be extremely careful if not using a vice as it can get out of hand fast. (Just as a warning, springs came out of mine which made it no longer “click” but still tightens down just fine)

Once you have got this far the work is over mostly but go ahead and seal up the outside of your cap and paint it up!

Someone mentioned finding out the psi rating on the pcv valve so you might look into that when buying but I do not actually know what this one is.

 

Nice. How much did it cost you to do or did you have everything laying around?

 

I just looked up a pcv valve and honestly bought one that just $5 online. I had the JB weld putting from plugging up my vtcs stuff on my intake mani, which worked out nicely. I also had some black spray paint laying around and the filter from a cheap ebay catch can that I am going to run sealed, but all in all you could probably do this for $5-20 depending on what you already have!
I’ll post up some results after I get my car back together. I also had my builder put in a small piece of metal on the underside to block splash up from the timing chain, since I have a gen 1 cover. Wish I had a pic, but it was a thin metal piece he bent to clear the timing chain and go under the oil cap. We used the screws already holding the other baffle piece in next to the oil cap hole.

 

Looks good man. Biggest thing I would look at when picking a check valve / pcv valve for this is cracking pressure. You want something with about as little of cracking pressure as possible, so it will easily open, and then at light spring pressure + gravity + crankcase vac will keep it sealed at all other times. The check ball in the oil cap breathers relies on gravity + vacuum alone.

On my miata I used a PCV valve + breather like this on the valve cover and the breather stayed perfectly clean....while the other normal breather (no pcv) was quite dirty. So the PCV valve was actually too much of a restriction to even make that vent useful.

No idea what a typical pcv valve cracking pressure is... here is the valve that I used for a similar project at one point, it has a cracking pressure of 0.1 psi:

https://www.grainger.com/product/CDI-CONTROL-DEVICES-Brass-In-Line-Check-Valve-6D914

edit: may not be that exact valve... they come in a variety of NPT thread sizes etc. But one just like that.

 

I wanted to put an update in this thread about the breather cap. I used it for longer than I should have, but wanted to say that if a gen 2 valve cover was used that it would work I am sure. Without a proper baffling system in place (such as the gen 1 valve cover) it just ended up soaking the breather filter and making an oily mess.

I hope that someone eventually tries this with a gen 2 valve cover and has success though! I may possibly get a gen 2 cover in the future and run a catch can system off of it. If so, then I will try this again with a $7 cap from autozone and see what happens lol