Oil catch can opinions

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I've read endless debate on the merits or lack thereof on catch cans. Most of the arguments run from "total waste of money" to "can't hurt" to "beneficial".

Could a small amount of oil vapor in an intake ever be a good thing and intentional by design? (Especially in a boosted engine.)

Thanks for your thoughts.
 
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Originally Posted By: jkasch

Could a small amount of oil vapor in an intake ever be a good thing?


Maybe, if naturally aspirated


Originally Posted By: jkasch
(Especially in a boosted engine.)


NEVER!!!!
 
Originally Posted By: jkasch

Could a small amount of oil vapor in an intake ever be a good thing(Especially in a boosted engine.)


You especially want to keep oil vapor out of the intake under boost.

Part-throttle cruise is/would be fine.
 
IMHO: I don't think any amount of oil vapor via the PCV system into the intake tract is a good thing. Many PCV systems have intricate "condensation" networks in them to help keep as much actual mist out of the intake tract (the last leg of the PCV system basically). In our GDI engines these days, since there is not injected fuel washing the intake valves like there in an the normal port injected engines, any oil mist gets gunked up on the intake valves as well as the intake tract (or part of it at least, depending on engine design). I have OCC on my turbo motor to help reduce this. YMMV.
 
It's not the best thing in any application, but those pesky crankcase vapors have to go somewhere that's not into the air or onto the ground.
 
Originally Posted By: jkasch
I've read endless debate on the merits or lack thereof on catch cans. Most of the arguments run from "total waste of money" to "can't hurt" to "beneficial".

Could a small amount of oil vapor in an intake ever be a good thing and intentional by design? (Especially in a boosted engine.)

Thanks for your thoughts.

Catch cans are nice to have. Oil vapor is always horrific to engine and sensor operation, because it leaves deposits and ends up causing knock to occur. Manufacturers don't use catch cans for environmental law reasons.
 
I don't like catch cans that have to be emptied periodically.

On my WRX I have a Crawford air/oil separator, version 2 to be exact.

It's a closed loop system that has lots of internal baffling, the liquid oil drains back to the pan, the remaining air is routed back to the inlet. The version 2 also has coolant routed through it to burn off any moisture that may accumulate inside.

Car burns absolutely zero oil since I installed it several years ago, and there is never a trace of oil in the intake (I've had the intercooler off a couple times since then)

They just came out with version 3, which they say is "ca smog legal," but I didn't get any grief about my version 2 a few months ago when I had to get emissions test done
 
Originally Posted By: Trav
I figure if they were worth a P hole in the snow the manufacturer would put them on as OE.
When everything is under warranty, engines don't usually have big oil vapor issues.
 
Originally Posted By: Trav
I figure if they were worth a P hole in the snow the manufacturer would put them on as OE.

Well oil separators are fairly common, no? My old E36 M3 had one. The NA V8 RS4 had a triple one, IIRC...
 
I DIY'd a catch can for this GDI Ecotec3 in the '16 Chevy to see what it might catch. In 2000 miles it caught about 2 tablespoons of whatever oil the dealer put in. Bought the truck with 2000 miles, catch can at 3000, changed oil to PPP 5w-30 @ 5000 and emptied the can. Not unhappy that I kept that spooge out of the intake and off the valve stems.
 
Originally Posted By: d00df00d
Originally Posted By: Trav
I figure if they were worth a P hole in the snow the manufacturer would put them on as OE.

Well oil separators are fairly common, no? My old E36 M3 had one. The NA V8 RS4 had a triple one, IIRC...


Sure they do but they usually don't use a garden variety PCV valve on those type systems either.
 
All the settled oil vapor I have seen on intake manifold was like shoe glue. My jeep for example had a 1/4" thick layer of th stuff that took hours to get rid of with all kinds of solvents and brushes. Fresh oil may be ok from port injectors such as Lucas ucl stuff, but burned up oil, no.
 
I don't know if it's a good thing or bad thing but is normal on all engines.

Two telling things about cans....

1. About 3 years ago there was a spirited debate on one of the F150 Forums with a famous can vendor. Claimed the Ecoboost's PCV system was "defective" and needed his can as it was the only one that would "fix the issues" and prevent gunk on the valves. Claimed he had one on his F150 from day one. When asked for pictures of HIS valves he never could get one. He also claimed more HP as the engine aged. When asked for dyno runs there were none.

2. The worst GDI engine guys (VW/Audi) played with cans and guess what? They still got no deposits.

I don't worry about the gunk in there. Even with all that stuff your engine will lead a long and productive life. They may be beneficial in certain applications (Racing, high boost, etc) but for stock or mild tunes it's a waste of money.
 
Appreciate all the comments. A couple of members on another forum were trying to make the case that a bit of oil vapor could be a good thing. I'm not buying it.
 
Originally Posted By: Trav
I figure if they were worth a P hole in the snow the manufacturer would put them on as OE.


Thats not how that works.

1,000,000 - cars sold
$4 - the cost of one widget per car
$4,000,000 - FOUR MILLION dollars for the auto company to add a $4 widget per car, if they sell a million cars. And since businesses are in the habit of trying to cut cost, while trying to earn a buck, any and all extra 'widgets" that are really not needed are ixnayed.
 
You assume all cars are built to a price point, some are not and still don't have one. They will sell you a $99 cheap POS catch can for your 1.5 million dollar Veyron to improve its performance.
Using an oil that doesn't go up in smoke like your mothers frying pan oil will probably eliminate much of the problem they are trying to fix with these things.
 
Volvo has a catch can that drains back to the sump. Would be a good idea if it was made out of better materials and easy to get at. So hoses break and it's hard to get to.
 
There are oil separators and labyrinths of various types on virtually all new engines. In the 70s-80s they were crude and oft built into the valve cover. Some more recent (post 2000's iterations) are cast right into the side of the block, because an oil/vapour separation function is so intended by the engineers, that they in-built it into the engine block casting. Manufacturers are to this day still patenting better and better mist/vapour separators, regardless of the "style" of PCV valve.

Yeah, it's worth something.
 
Originally Posted By: bubbatime

Thats not how that works.

1,000,000 - cars sold
$4 - the cost of one widget per car
$4,000,000 - FOUR MILLION dollars for the auto company to add a $4 widget per car, if they sell a million cars. And since businesses are in the habit of trying to cut cost, while trying to earn a buck, any and all extra 'widgets" that are really not needed are ixnayed.


Or you spend the $4, raise the price of the vehicle $10 and nobody will notice the $10 on a $30-40k vehicle. Few would dismiss a car over $10.

If it did the things claimed (HP gains, MPG gains, etc) then it would be a steal for manufacturers as it would be a cheap boost to CAFE...

You may even reduce warranty costs if it actually did something. The fact that a manufacturer of a can (supposedly the best) who owned a speed shop could not provide pictures of clean valves or before/after dyno #'s was all the data I needed to see. They are useless for stock applications. He also tried to say MPG would go down due to the valve deposits. Unfortunately for him I have records of nearly ever fill up for well over 100k miles in 1 and 30k in the other and MPG is roughly the same over all those miles.
 
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