TOPIC: Silicone Vacuum Caps

OK Gadgetfolks, I've found a source for silicone vacuum caps on Ebay.

These are for 5/8" dia. fittings, this and other sellers on Ebay have similar for lots of sizes.


Got 10 of 'em for $7.99 w/ free shipping, came from Hong Kong.

Being silicone, ought to last darn near forever--though I've read that silicone caps dont like gasoline, which may degrade 'em. Might consider using some type clamp on 'em, but they fit snug on the 5/8" fittings on my breather hose oil catch bottle. Here's how they look:



Every black rubber vac. cap I can find is junk quality, they can crack and die from heat in months. Take a look around there are other sellers on Ebay too, I think McMaster-Carr has similar.

Tracy G

that looks like an 18/10 stainless steel water bottle! you're using it as an AOS catch can?
How does the hard plastic stopper hold up to the heat in the engine bay?

Yup, Greg, that's just what it is. I've done writeups on this and a BMW cyclone AOS in the Index. the black plastic cap has been fine, I have this located away from high heat. I have a tee in the breather hose on Subie I use the blue silicone cap on the tee in winter, and reverse things for summer re: the PCV system. Meaning I connect the PCV up "stock but modified" for winter, running thru this catch can AND the BMW cyclone separator, then a restrictor in the PCV hose just before the man. vac. nipple. Have to have some active crankcase ventilation w/this motor in winter, too much condensation not to. I restrict the flow, lengthen the hoses, use large dia. hoses, and run the PCV gasses thru 2 stages of water/crud separation. Bigger I.D. & longer PCV hoses reduce velocity, and the restrictor cuts flow volume.Slowing down the gas velocity helps entrained liquids to drop out better. Restricting total flow is a step back towards original intent of PCV re-route. The Subaru's crankcase ventilation system uses big dia. hoses, and tends to pull oil out from the valve cover nipple. The way I'm doing it, I'm not seeing water condensation evidence under oil fill cap so far, and the 2- container AOS deal has trapped some oily water already. But it's less potential flow than the all-stock PCV system would be, I've kinda "tuned" the PCV on this car. The water bottle catch can will hold lots of crud/water, and has the Mopar valve cover breather filter as it's outlet fitting. I stuffed a stainless pot scrubber in the bottle as extra condensation area. The cyclone separator is the 2nd stage, then the hose from that goes down to the manifold vac. nipple. I could post pics of how this is installed, it's a bit visually confusing.

To clarify- winter setup is stock PCV hose connections, w/long oversize diameter hoses thru 2 AOS'es and a restrictor just before man. vac. nipple.

For summer I swap the breather hose tee cap and the PCV man. vac. hose, that is,back to a "regular PCV re-route".

Silicone and vinyl caps hold up fine, today's rubber caps die in months for me.

Tracy G

after I posted my initial response/query, I found the thread with part #s...

more, again, to ponder and investigate. good thing it's going to be a long, cold winter.