Catch can return line?

[LeeRoy]

So how quick does a can fill up then?

[WDE_BDY]

A lot will depend on the motor, how its driven etc, lots of around town driving tends to give more moisture from regular temp changes, higher revs tend to give more blow by, 4A's for example often have oil drain probs from the head. A sight level on the side of the catch is probably the best approach for a street car, race cars will get checked over more regularly anyway so not as important.

Callum

[Thomas]

Callum: I meant on cars that run stock catch-cans.

[WDE_BDY]

Stock factory setups have to be able to go 10,000ks between services, an overflowing catch can would cause problems. I haven't really come across any normal production cars with a can (have heard of a few though), what have you seen them used on? I guess if you don't want to worry about emptying it you could have the drain halfway up the can, hopefully the worst sludge etc would just sit in the bottom.

Callum

[LeeRoy]

So since it collects with condensation etc wouldn't it be a bad idea to run it back to before the turbo as then your just feeding this junk back into your motor.

Alternatively you could just have an atmospheric vent, but then your engine bay fills up with oily residue.

- LeeRoy

[Thomas]

My last car had one (Starion). I've seen a few around but you're right - they're not very common at all. On all setups I've seen the can empties to the sump.

[WDE_BDY]

So since it collects with condensation etc wouldn't it be a bad idea to run it back to before the turbo as then your just feeding this junk back into your motor.

Alternatively you could just have an atmospheric vent, but then your engine bay fills up with oily residue.

- LeeRoy

The common plan is steel wool or something similar in the can to condense the fumes as much as possible before its fed back to the intake or vented. generally anything getting to the intake should still be pretty hot though so won't be too much of an issue. Remember, the only reason most people plumb back into the intake is for vacuum and because it is generally illegal not to due to emissions. Your engine effectively needs to be a sealed system, so all blowby etc is burnt through the combustion chamber. If you chose to vent the can a small filter and a decent sized can will generally minimize oil mist and fumes.

Callum

[feral4mr2]

What collects in the catch can is all the impurities that have been burnt off from the engine oil. Mainly moisture that gets condensed as it cools in the catch can. Rememeber most of what is collected is fumes, you don't get big quantities of oil pumping straight into your catch can except under pretty harsh race conditions.

Callum

indeed, the bold print above is why i wouldnt return the build-up in a catch can back to the sump.

WDE_BDY, i made my own catch can (go the PVC. ) and i filled it with stainless steel scourer's, to catch the oil mist. better then steel wool as the steel wool over time may break up and allow bits of it to be sucked back into the engine (if running a vacum return catch can).

[hybridaddy]

this is my daily driver setup.
i made the lot myself including the drainback catch can which works well.
its full of stainless steel wool to seperate the oil air mixture,i havent had one drop of oil come out of it so far

[mic*]

Remember, the only reason most people plumb back into the intake is for vacuum and because it is generally illegal not to due to emissions. Your engine effectively needs to be a sealed system, so all blowby etc is burnt through the combustion chamber. If you chose to vent the can a small filter and a decent sized can will generally minimize oil mist and fumes.

Callum

The first part there is a little wrong. Every PCV system ive seen is plumbed back into the intake PRE-throttle. This means the pressure is always ATM, unless you have a turbo, in which case they are either plumbed before the turbo, or have a one-way check valve so that the POSITIVE pressure of blowby etc displaces the gases when OFF boost.

(EDIT: Just thought Id add there is always high gas velocity at a factory venting point, which im sure helps draw gases out. Other than the environmental issue, this is another problem that i see with "vent to air" setups, that the system may not really breathe as well...)

I agree that what goes back into the sump will be deteriorating your oil quality. I guess its a question of how often does the can require emptying relative to oil changes? If it was often, you might do it (the drain back) so you only have one thing to worry about - oil changes, just a bit more frequently than you used to.

[30psi 4agte]

I DO NOT RECOMMEND PLUMBING IT BACK IN !!!!!!!!!!!!!!!!!!!!

Any one that has emptied a catch can will know the state of the oil that collects in there.
Would you pour this back into your engine ????

I think not!

[hybridaddy]

I DO NOT RECOMMEND PLUMBING IT BACK IN !!!!!!!!!!!!!!!!!!!!

Any one that has emptied a catch can will know the state of the oil that collects in there.
Would you pour this back into your engine ????

I think not!

some engines will collect condensation in the can,some wont.

[WDE_BDY]

The first part there is a little wrong. Every PCV system ive seen is plumbed back into the intake PRE-throttle. This means the pressure is always ATM, unless you have a turbo, in which case they are either plumbed before the turbo, or have a one-way check valve so that the POSITIVE pressure of blowby etc displaces the gases when OFF boost.

I have to disagree, pre or post the throttle plate there is generally vacuum most of the time. Post throttle there is more vacuum (especially on throttle lift off), however pre throttle there is still significant vacuum. Take the air cleaner off any N/A car and put your hand over the inlet, you will feel pretty significant suction whenever the engine is given a rev.

Callum

[mic*]

Callum I agree to some extent. At higher revs, the filter can be restrictive enough to the massive airflow & creates a weak vacuum. If its any more than "weak" its time for a new filter.

Take the filter off and put your finger down the inlet pipe. Its just fast flowing air at ATM pressure... If you put enough of your hand over the inlet to restrict it, you start to feel your hand being sucked. If a filter caused this sort of restriction you wouild use a tank of fuel to get out your driveway.

[kingmick]

you only need to plumb back if your lazy or you use to small a catch can! if your engine is topping up to much oil at revs id be opening up the oil return a bit and or putting in an extra return from the head.
if you use a filter on the top like all decent catch can setups{i wouldnt even pump the blow by gas into the intake as it will still lower the oxygen level in the charge} the moister is sucked in threw the filter when you stop. even dry sump ststems you get this on some setups, and the water in the oil makes the oil drop its boiling point and lowers the life of the oil.
if your to lazy to check the level by taking the filter off or the engine blows that much out, get a bigger catch can.