Oil catch cans: Practical or Placebo?

WonkoTheSane wrote:

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!

Mazda doesn't think you should be taking them apart They seal with RTV.

Fair enough :) Have you ever seen problems with them if they've never been apart?

Nope.

In reply to Tom_Spangler:

So what they do has been covered here but I'll add that they're very useful to have for direct injection engines to keep the backs of the valves clean. I run one on my MS3, which normally routes into the intake tract, because carbon buildup will start at under 30k miles. After that there's a noticeable performance decrease and you have to walnut blast the valves. That's a giant PITA.

Water-meth or 5th port injection helps, as they wash the valves, but I'm not willing to run one of those setups on my daily driver.

It does get interesting when you accidentally fill it up. I experienced that when the turbo shaft separated and dumped oil into the system.

The0retical wrote: Water-meth,but I'm not willing to run one of those setups on my daily driver.

If you saw how clean the valves were in my 250k mile 26 year old clacky volvo was with meth, you wouldnt say that haha. And that i filled the tank once a month with washer fluid, like i would anyways the washer tank..no real extra effort.

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.

Yup!

Also, as far as ways of plumbing, there are lots of possibilities for complicating things but in general you would install a catch can on the breather tube going to your intake, or have the can itself be the breather for the crankcase (i.e. have its own filtered air inlet) and seal the hole on your intake system that used to be the breather. You COULD put another catch can between the crankcase and the intake manifold but i personally feel that it's a bit pointless considering that normal PCV 'gasses/consumption' don't cause issues anyway. When you go into boost, your pcv valve should close and stop flowing anything, and all the positive crankcase pressure generated should go out the breather to your catch can. If you can't go into boost because you don't have a turbo, then great! You probably don't need a catch can either!

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

Or, put another way, if you have very little blowby you probably have very tight ring gaps that are going to cause your ring ends to butt and try to seize the piston in the bore and crack off your ringlands when you increase the heat in the cylinder way past stock. Pick your poison i guess?!

One of the very first things I did after getting the FR-S was put in an air/oil separator (catch can) from Radium Engineering.

After ~700 miles:

After ~4k miles:

Seems to consistantly be a mixture of oil and fuel...smells entirely like fuel with a hint of oil. Basically every oil change I have been dumping it out, nice that it has a dipstick to check the accumulated level without having to unscrew the bottom every time. Been thinking about going with water/meth injection as well to mainly help clean the valvetrain and pistons.

In reply to chiodos:

Helps that much? HTP makes a really nice tank for the car.... Wonder if the wife would notice one more thing.

In reply to The0retical:

You tell me, i made my own kit with a $20 chinese 100psi pump off ebay, a meth nozzle from snow performance on clearance for $20 (mcmastercarr has them as well high pressure water spray nozzles) some hose a relay and a old nos solenoid i had lying around. So like $60 in parts? I used my washer tank cause it was big and had a low level sensor with light in the dash. Was a $400 car so i didnt care about it. Windshield washers still worked which was nice haha. Used winter blend washer fluid from walmart (cheaper the less adulturants in it so only meth and water and a bit of blue dye)

Intake manifold was just as clean but dont have a photo of it on photobucket so its not just the fuel cleaning the valves like some might argue.

Catch cans don't really help much in a normal consumer engine. Most of the "oil" its collecting would normally just recirculating in the crankcase anyway, and catch cans trap mostly water vapor, or fuel that was diluting the oil. Also like mentioned the PCV system in the engine does have some separation capability. Now on a high output, boosted forged internal engine, that makes more sense as you have just more blowby in general.

The theory that with DI engines the deposits on the back of the intake valves is caused by oil blowby in the intake tract doesn't really explain the whole issue. Modern engines also use a lot of valve overlap through use of the VCT phasers, during low engine speed high load on a turbo engine this leads to a lot of soot and carbon buildup on the valves. Think of it as internal EGR, without an EGR valve, if you've ever seen a gasoline engine EGR valve or cooler, you know how much carbon deposits those build up!

The other idea with reducing oil in the intake tract, to protect the turbo or reduce knock from oil ingestion, also doesn't really account for all the knock/preignition issues on DI engines either. The better theory for main PI causes relate to oil blowby within the cylinder, during ring flutter or even normal blow-by. These hot oil "droplets" that form in the combustion chamber are the main source of pre-ignition, especially when you consider the oil is diluted with some amount of fuel.