Oil catch cans: Practical or Placebo?

I've recently become aware that a lot of people are running oil catch cans, particularly in boosted motors. The 5.0 Coyote is also a popular application that I'm obviously interested in, but I'm mainly interested for my Expedition, which has the Ecoboost 3.5L V6.

As explained here, the basic idea is that they help keep crud out of the intake tract by catching all the oil, fuel, water, and whatever else that comes from blowby. It gets caught in the can instead of going back into the intake manifold and then back into the engine. You then empty the can periodically. The idea is that your intake and valves and everything stay cleaner.

But what do they really do? Based on a superficial understanding of engines, it seems like it can only help, right? But part of me thinks that if this kind of thing was really helpful or necessary, the factory would be doing it already. And what if the can becomes clogged or water freezes in it? Does that plug up the whole PCV system? Because that can't be good.

So, what do we think?

I think normal consumers haven't got the patience to fiddle with something like that.

Some cars DO have a factory oil separator type thing.

A few things: 1. Blowby gets higher with cylinder pressure, so even an engine with 'good' ring seal is going to have a lot of blowby if you are doubling the horsepower. 2. Any blowby that exceeds the flow of the PCV valve (which is 0 when in boost) goes out the breather tube which leads to your intake pre-turbo. If you have an air to air intercooler it's a good chance it's the lowest point in your system and that liquid oil will collect there, making it difficult to clean/remove. 3. Oil lowers your effective octane, so if your engine is breathing enough of it it could cause detonation problems.

Taken together, those are plenty of reason to keep your blowy separated from your intake tract as much as possible. There are other ways to do it besides a catch can, but that's the most common solution. Essentially, the more power you make, the more blowby you have and the more sensitive you are to fuel octane, the more you need a catch can.

Pcv is emissions control just like an egr, if you run high pressures you'll need to vent the head and block to a can, will prevent oil blowing out of your dipstick or pushing past seals not designed for pressure...30psi teaches you things

Huh, I thought that's what the bottom of my intercooler was for.

If you're using the car hard yes.

I know on the BRZ, even the N/A guys get quite a bit in the PCV side catch can with hard/track usage. I ran one on my Coyote Mustang on the passenger side, even after only 5000 street miles, it probably accumulated 1-2 tablespoons of oil.

The crankcase side on the BRZ isn't needed until you've added booooooooooost.

These are pretty much required for an FD that sees track duty. My catch can is completely full after 2 hours of lapping. Failure to remember to empty it may have you asking whether you just blew your motor due to the unusual performance characteristics that result.

I run a can on the PCV side of the system in the Jeep. It doesn't pick up a ton of oil, but it does catch some. I haven't put a can on the vent side to the airbox, but judging by grime on the throttle body, etc. it doesn't blow a whole lot of oil through that side (and it doesn't spend that much time at sustained WOT anyway).

Tom_Spangler wrote: But part of me thinks that if this kind of thing was really helpful or necessary, the factory would be doing it already. And what if the can becomes clogged or water freezes in it? Does that plug up the whole PCV system? Because that can't be good.

You just answered why.

Many Euro cars DO use catch cans, in a sense. They aren't separate units like aftermarket, but the prime example I can think of is the big tank under the intake manifold on BMW 6-cylinders that occasionally freezes..

Nissan's sr20s turbo and n/a, got oil recirculators on most engine variants, but some had a larger chamber/maze built into the valve cover. Both systems were designed to drain the oil in the motor while venting water vapor back into the intake. If you can find a good warm spot in the engine bay to place the catchcan you can let it self drain back into the oil pan. It is better to be in a warm to hot spot to evaporate the water that accumulates with the oil.

I remember Guys would chuck the oil recirc cans thinking they were worthless emissions parts. Later on they would post "blew my turbo seals" and sell their turbos cheap as needing to be rebuilt

If this is oil blow-by, would it be possible to route it back to the sump, rather than a catch can? Or, is it polluted, that you wouldn't want circulating through the lubrication system?

RealMiniParker wrote: If this is oil blow-by, would it be possible to route it back to the sump, rather than a catch can? Or, is it polluted, that you wouldn't want circulating through the lubrication system?

Yeah, I think that's the idea. It's full of unburned fuel and other crap that dirties up the oil.

So, what I'm hearing is that, in a daily-driven NA car, they probably don't offer that much advantage, but they can't hurt. Where they are really useful is in a boosted car or one that's driven hard.

I think I'll get one for my Expedition, then. Thanks, guys.

I always look at it as top cylinder lube, and water injection.

Anyone remember oil bath air cleaners ?

If you are getting a lot of blow by, cylinder sealing is not adequate.

RealMiniParker wrote: If this is oil blow-by, would it be possible to route it back to the sump, rather than a catch can? Or, is it polluted, that you wouldn't want circulating through the lubrication system?

Alfa's PVC system did that- used the flow to spin the oil in a container, and there was a small drain on the bottom to put back into the pan. The plastic ones were better- as they didn't rust.

E9x's w/ DI are susceptible to carbon buildup in the intake port/ valve area, oil vapors bake on the hot dry surfaces. Non-DI not as much as there is fuel to wash the tract down. Oil still gets burnt through the engine DI or not. Opinions vary on walnut shell media blast of the N54 intake port/ valve area from 35K miles to wait till a fault code at higher mileage. Dealers want $700+ for that job. I just pieced together a media blast kit for < $250 all in and have a BMS separator/ OCC on order, hope to get that job done w/in a few weeks. Will post pics then.

Matter of fact a JLT separator/ OCC is due for delivery anytime today for the S197, prolly overkill as I don't thrash on it but ya wanna protect yur stuff.

My indie mechanic related several stories of DI engines both NA and turbo of several mfgs. that have excessive carbon build up in the intake tract enough to throw a code at 30K +/-. Dealerships may not be prepared to deal w/ this situation and may or may not cover under warranty, not gospel tho.

I'll probably install a Moroso OCC on the '14 Silverado while I'm at it. Might be cheap insurance for the long run.

I'd research your vehicle per forums JIC for the word on carbon build up and any benefit of OCC's.

Im planning on running one once I go turbo but should I think about one for my NA miata? It gets driven hard 90% of the time and I wanna keep it going for awhile.

One thing to understand is that almost everyone who installs a catch can themselves plumbs it wrong.

I've got a factory oil separator on the Targa Miata, it's an option that comes off one of the track Camaros. Pretty cute, it's built into the oil fill cap so the extracted oil goes right back into the engine. If you sequester the oil in a separate container, it's no longer in your sump so your oil level is going down.

The Mazdaspeed Miata had a separator with a drain into the sump. Under hard driving, it would actually siphon oil up and into the engine. You have to put a check valve in the drain line, but then it works nicely. Heck, Miatas have had little separators built into the valve cover vents since day 1 - most people don't find out about them until they disassemble the valve cover, don't seal up the separator and suddenly have oil consumption problems.

Keith Tanner wrote: One thing to understand is that almost everyone who installs a catch can themselves plumbs it wrong. I've got a factory oil separator on the Targa Miata, it's an option that comes off one of the track Camaros. Pretty cute, it's built into the oil fill cap so the extracted oil goes right back into the engine. If you sequester the oil in a separate container, it's no longer in your sump so your oil level is going down. The Mazdaspeed Miata had a separator with a drain into the sump. Under hard driving, it would actually siphon oil up and into the engine. You have to put a check valve in the drain line, but then it works nicely. Heck, Miatas have had little separators built into the valve cover vents since day 1 - most people don't find out about them until they disassemble the valve cover, don't seal up the separator and suddenly have oil consumption problems.

Keith,

Do you have more information on this setup? I would not mind having something like this for my LS Exocet.

There are plenty of DIY tutorials online of home built separator/ OCC's put together on the cheap. If after research on your engine/ vehicle you have any doubts or inclinations put one together on the cheap and see whatcha catch. Build or spend accordingly.

Papabear wrote:

Keith Tanner wrote: One thing to understand is that almost everyone who installs a catch can themselves plumbs it wrong. I've got a factory oil separator on the Targa Miata, it's an option that comes off one of the track Camaros. Pretty cute, it's built into the oil fill cap so the extracted oil goes right back into the engine. If you sequester the oil in a separate container, it's no longer in your sump so your oil level is going down. The Mazdaspeed Miata had a separator with a drain into the sump. Under hard driving, it would actually siphon oil up and into the engine. You have to put a check valve in the drain line, but then it works nicely. Heck, Miatas have had little separators built into the valve cover vents since day 1 - most people don't find out about them until they disassemble the valve cover, don't seal up the separator and suddenly have oil consumption problems.

Keith, Do you have more information on this setup? I would not mind having something like this for my LS Exocet.

It's the 1LE kit: Linky

In order to get the hood clearance, I swapped my valve covers side to side so the filler is at the rear of the driver's side head.

As for the online DIY tutorials, read as many as you can. We've seen so many jacked up oil separator designs it's not funny. Most common seems to put one side on the valve cover vent and the other on the PCV valve on the valve cover. So there's absolutely no airflow through it as there's no pressure differential.

iceracer wrote: I always look at it as top cylinder lube, and water injection. Anyone remember oil bath air cleaners ? If you are getting a lot of blow by, cylinder sealing is not adequate.

You may be amazed at how much crankcase gases are normal.

Chew on this... on a 350hp car, if there is 1% blowby, that is as much blowby gases as your average lawnmower's exhaust at WOT.

My old triumph just had a tube from the factory poking out of the block pointing at the ground. SVRA frowns on dumping oil on the track.

Keith Tanner wrote: Heck, Miatas have had little separators built into the valve cover vents since day 1 - most people don't find out about them until they disassemble the valve cover, don't seal up the separator and suddenly have oil consumption problems.

Hey Keith,

Do you have a good detail on how to seal this properly? I've never gotten any seals for it in any valve cover kits, and a quick google search is revealing all sorts of hokey things.. I do have some oil consumption issues, but I've never taken apart that maze, either..

Thanks!

I'm in the process of boosting my engine and wanted to be ahead of the game by putting a catch can in now. Was looking around my shop for a canister to make my own contraption. Then I found quite a few on ebay for $15-$20. My time is worth more than that. A $20 experiment isn't much of a gamble.

I'm a strong believer, especially on boosted cars. I still keep my diagrams up on my server from when I had an SRT-4 so the community can use them (I also have installed pictures if someone is interested).