Oil smoke/mist coming from oil catch can????

[JamesB]

I fitted an aftermarket oil catch can a few months back with the following set up. The oil mist return from the back left of the rocker cover goes under the plenum across to the catchcan that sits near the charcoal canister. The other rocker cover mist outlet (t piece) goes to the catchcan as well as running down to the crankcase return (where origional oil/air separator was). There is a breather filter on the other end of my catchcan.

My question is - why the hell is it huffing out oil mist/smoke from my breather at idle?? Is it cause ive connected it to the crankcase? Is there some other reason. Also, the hose going off the back left rocker cover outlet doesnt seem to clear itself too well. I assume its cause it used to have a vacuum pulling the mist out? Is there another way of plumbing this cause when it gets oiled up, my car PUMPS out smoke from the exhaust - not cop friendly.

Cheers.

 

[Fast Guy]

I don't have a catch tank, but this is how my oil separator is plumbed in.

Hose from top right of rocker cover goes to top of separator, hose to right of that returns to inlet and the other hose is drain to sump. The hose on the back left of the rocker cover is untouched.

Have you done a compression test, it is possible you've just got alot of blowby.

I can't see why you need two feeds from the rocker cover to your catch tank, surely one would be enough?

Try fitting an uprated oil separator

 

[GINGA]

Heavy breathing and smoke sounds bad best to get a compression test done

 

[JamesB]

It shouldnt be blow by - had a compression test done a few months back and it was fine. Blow-by isnt really a idle type problem - thought it was when it was being boosted. I have disconected the oil mist return to the throttle bodies and to the inlet (why pump oil mist into my air/fuel mix right) so i found it odd to be breathing oil like that.

 

[turblio]

Hate to put the downers on it but..
thats what mine was like a week before it mangled apistola (mexican for piston :lol: ) and it also had good compression
but its great now as I had it all made better
Frank

 

[Keira]

just to put a bigger downer on it,

discodave blew ringlands twice, both times a compression test showed no problem

 

[Fast Guy]

Blow-by isnt really a idle type problem -

If your rings are worn out, you'll get blowby at idle. You should have a slight vacuum in the sump due to the breather system sucking it out, but if you have quite badly worn rings, the blowby will start to pressurize (slightly) your sump at idle. If you put your finger on the end of the dipstick tube you will either feel a vacuum or pressure.

 

[JamesB]

If my rings were worn Id expect it to blow smoke when driving - at the moment it doesnt at all, yet this mist issue has been going on for several months now. The only time it blows oil smoke from the exhaust (and clouds off it) is randomly after sitting at the lights for a minute or so. But again, this only happens 1 in 5 time at a guess. The mist pipe from the back left as already said doesnt clear itself and Im adiment that this excess smoke is the rocker cover's vacuum at idle sucking this back thru. If I do disconnect that pipe, the catchcan still breaths mist. ?? Do you understand my confusion. Its like the mist is going straightr thru the catchcan and out the breather filter - despite being set up ok :? Me dunno

 

[Anonymous]

Do this test. Remove the dip stick and get some hose that fits snuggly over the dip stick tube (clamp it on). Run the hose in to the cabin and tape or clamp a ballon to the other end. Take the car for a drive around the block. If the balloon inflates, you have excessive blowby (but by your symptoms we know this already).

Have fun.

Ben

 

[Fast Guy]

If my rings were worn Id expect it to blow smoke when driving

I never mentioned smoke Blowby is the combustion gases getting past the rings. If your rings are worn then these gases will still go past the rings into the sump at idle. ( I had plenty of pressure at idle on a previous car until the engine was rebuilt then I only had vacuumm)
You may get smoke at idle as the oil still get's burnt, but it'll chances are it'll show up more when driving when there's abit more action going on

 

[JamesB]

yep, bugger. The dipstick hole is spitting oil. Sooooo, how long does it take of spirited driving at 1 bar til they're screwed.

 

[Anonymous]

More screwed that it is already? I think now would be a good time to stop driving it really. If you’ve mashed the ring lands on a piston (sounds like you have) then you don’t want tiny piston chunks flying around inside the engine scoring up the engine and turbo bearings, cams, bores, etc.

Remember that the engine failed because of detonation, so just rebuilding it won’t stop it from happening again. Turn the boost down, use better petrol, have all the injectors cleaned and balanced, fit water injection, go for a front mount intercooler, maybe even use lower compression pistons.

When you strip the engine check all of the piston crowns for signs of pitting to see the extent of the problem. It might just be you have an injector with restricted flow that caused it, but if all the pistons show signs of knocking it’s unlikely. Check that the main and rod bearings are still round and don’t have flat spots. If in doubt, replace them all. Also with the engine out replace the water and oil pump.

 

[JamesB]

Ben - do you think its as open and shut as that??

Its a 14yo car - I expect things to get worn over time. Its only has a couple incidences of det in my time of ownership. I picked up on it straight away and removed the boost controller. Id be inclind to think that this isnt abnormal wear.

Or am I being naive?? :?

 

[Keira]

Or am I being naive?? :?

bens spot on,

without knowing milage cant comment on whether its just wear and tear, but the nissan engine is very tough if looked after, i know of several that are up in the 100000's without a rebuild 8) ,

discodave did the full rebuild but didn't really look at why it broke in the first place, it broke again 2nd rebuild he went abit further and looked at sorting the fueling side aswell iirc, like ben says, one sh! tty injector and the same will happen again.

do it once and do it right