What is the purpose of a oil catch can?

[HAP]

It may be quite a daft question but I've been seeing a lot of clio 182's with oil catch cans/tanks lately, what is the purpose and benefits of them and should I get one for mine?

 

[Krarl]

No oil vapours going into the intake for a cleaner burn

Instead the oily vapour gets 'filtered' inside the catch tank and then the air just escapes but the oil is trapped within the tank which you just empty every so often

 

[Danith]

have wondered this myself to be honest. A lot of folk replace the PCV system on the TSI engines and put a catch can. I understand what a catch can does, but never really understood why it was a necessity.

So oil vapours currently get recycled into the inlet? to be burnt off?

 

[Krarl]

Yeah. TSI engines suffer from carbon buildup on the inlet valves from the oil. An F4R is an IDI (indirect injection) engine so sprays fuel onto the back of the inlet valves so you get a fuel, air and oil mix hitting the inlet valve

On a TSI they're direct injection like most diesels. So your air and oil hit the inlet valve but there's no petrol there to wash away any carbon stuck to the valve. Over time your inlet valves get so coked up that your engine just gives up on life

 

[Danith]

Yeah. TSI engines suffer from carbon buildup on the inlet valves from the oil. An F4R is an IDI (indirect injection) engine so sprays fuel onto the back of the inlet valves so you get a fuel, air and oil mix hitting the inlet valve

On a TSI they're direct injection like most diesels. So your air and oil hit the inlet valve but there's no petrol there to wash away any carbon stuck to the valve. Over time your inlet valves get so coked up that your engine just gives up on life

Ahhhhhh gotcha. I didn't even know that oil was chucked into the inlet valve! Thought was just fuel and air. Everyday's a learning day. so the catch can on a TSI is to stop/reduce the coking up over time?

 

[Krarl]

Ahhhhhh gotcha. I didn't even know that oil was chucked into the inlet valve! Thought was just fuel and air. Everyday's a learning day. so the catch can on a TSI is to stop/reduce the coking up over time?

Yes mate, if you want a good vid to watch then this is the one for you



This guy knows his s**t when it comes to VW's. He was some sort of master tech iirc. Properly knows his stuff though, right VW perv 😂

 

[Danith]

Yes mate, if you want a good vid to watch then this is the one for you



This guy knows his s**t when it comes to VW's. He was some sort of master tech iirc. Properly knows his stuff though, right VW perv 😂

wow, that's oil?? looks very thin

 

[frayz]

wow, that's oil?? looks very thin

Oil vapour but most of that will be condensation/water.

 

[clio tyres]

wow, that's oil?? looks very thin

+ Water

 

[bashracing]

This is a good video with regards to carbon buildup on TSi engines

 

[Danith]

Oil vapour but most of that will be condensation/water.

Condensation in the catch can? Or that's all that gets chucked back into the engine?

 

[frayz]

Condensation in the catch can? Or that's all that gets chucked back into the engine?

On a non recirculating system as show, its condensation that forms in the cold catch can when the engine is switched off. Some people choose to run a RTS (Return to sump) setup that will allow the oil caught to return to the oil pan. As you can imagine, that amount of condensation is built up over quite a period of time, on an RTS setup, it will only ever be a small amount of moisture in the system and generally gets burnt off and the oil is changed before it can really become an issue.

I used to run an RTS setup on my Impreza that wasnt a catch can but a proper AOS (Air Oil Separator) with VTA (Vent To Atmosphere) and RTS.
Most impreza guys do it that way, due to the amount of oil you can displace up the breathers on a hard launch.

 

[MLB]

How much water/oil mix would you expect to empty out of the catch can on an F4R?

 

[Krarl]

How much water/oil mix would you expect to empty out of the catch can on an F4R?

Depends how worn your rings are

 

[frayz]

How much water/oil mix would you expect to empty out of the catch can on an F4R?

Depends on many factors, mileage, engine usage interval, type of driving done, engine health, forced induction or NA etc.
1000 miles of 20 mile journeys over 4 months in winter vs 1000 mile sprint across Europe over a few days would net a very different outcome.

 

[banhama]

On an FR4 engine do you cause any issues by venting to atmosphere through a catch tank, in that you lose the suction (PCV?) effect of having the vent pipe plugged into the intake.
Or is it best to route the pipe through the catch tank and back to the intake?

 

[Donny_Dog]

On an FR4 engine do you cause any issues by venting to atmosphere through a catch tank, in that you lose the suction (PCV?) effect of having the vent pipe plugged into the intake.
Or is it best to route the pipe through the catch tank and back to the intake?

You'd bung the hole in the inlet. You can't feed it into the catchcan as it'll bypass the throttle body and have unrestricted air in the manifold.

A breaker we bought near 10 years ago did just that (not a Clio). "It revs like it has a mind of its own" lol.

 

[banhama]

You'd bung the hole in the inlet. You can't feed it into the catchcan as it'll bypass the throttle body and have unrestricted air in the manifold.

A breaker we bought near 10 years ago did just that (not a Clio). "It revs like it has a mind of its own" lol.

So you have to lose the positive crankcase ventilation that sucks vapour out of the crank case if you use a catch tank?
If you just vent the tank to atmosphere, and bung the inlet hole of course, you no longer have any suction.
Does that in turn decrease the effectiveness of removing oil and water vapour from the crankcase?

I guess what I'm asking is:
Is the OEM vent routed back to the intake just to burn off the oily vapour just for some anti-pollution reason, or is it routed that way because the suction is needed to properly ventilate the engine?

 

[MLB]

Depends how worn your rings are

Depends on many factors, mileage, engine usage interval, type of driving done, engine health, forced induction or NA etc.
1000 miles of 20 mile journeys over 4 months in winter vs 1000 mile sprint across Europe over a few days would net a very different outcome.

Yeah I'd asked the question and thought it would be a bit of a piece of string question, haha.

Thanks guys

 

[R3k1355]

So you have to lose the positive crankcase ventilation that sucks vapour out of the crank case if you use a catch tank?
If you just vent the tank to atmosphere, and bung the inlet hole of course, you no longer have any suction.
Does that in turn decrease the effectiveness of removing oil and water vapour from the crankcase?

I guess what I'm asking is:
Is the OEM vent routed back to the intake just to burn off the oily vapour just for some anti-pollution reason, or is it routed that way because the suction is needed to properly ventilate the engine?

Bit of both.

You need the crankcase ventilation to equalise pressure across the engine, what with all the pistons flying around and such. If an area becomes pressurised for whatever reason oil flow there will be compromised as the pressure is forcing it away.

RB and CA engines suffer from this, excess pressure in the crankcase leads to oil taking longer to drain down from the head, you get less oil in the crank case and end up wasting crank bearings.
Some of the twincharged TSI engines also had some similar breathing problems I seem to remember.

 

[Donny_Dog]

So you have to lose the positive crankcase ventilation that sucks vapour out of the crank case if you use a catch tank?
If you just vent the tank to atmosphere, and bung the inlet hole of course, you no longer have any suction.
Does that in turn decrease the effectiveness of removing oil and water vapour from the crankcase?

I guess what I'm asking is:
Is the OEM vent routed back to the intake just to burn off the oily vapour just for some anti-pollution reason, or is it routed that way because the suction is needed to properly ventilate the engine?

The post above is spot on. The oil draw back was an issue, I recall it was the same in the TU generation of Talbot/Peugeot/Citroen. However they must have overcome it, or realised it had limited operational impact, because they blocked the PCV system off on the later incarnation (and still modern dayish) JP4 variantion of the J4.
These are not race engines though, so I'd bare that in mind. Tolerances for mainstream Vs Motorsport will obviously differ.

The vacuum isn't needed to get the catch can filled. The crankcase pressure alone will fill it, if your rings are shot. Even if they aren't, likely will be some blow-by on a used motor.
I rebuilt an engine to spec, bedded the rings in etc. But ran an open air filter for the crank ventilation. On the Dyno, coming off full boost, what I could see was what the contents of the catch can would have been, if I'd have run one!
At least nothing will rot in the engine bay now.