Engine ventilation - is this work as it should?

[vit]

Hi all Gurus here,

I have a Tacuma, the question about it's engine, 2l 16-valves; 130 000 km. I'm not sure what prev. owner has with it, but when I've got it it has crankcase ventilation stuffed up. Mechanic who changes timing belt suspects that some kind of "overheating" has place (signs of coolant in suspicious places?). Car newer run "great" - just mediocre. Eats a lot of gas. Engine is noisy. I'm trying to play with it from time-to-time, cleaning, changing oil, filters, spark plugs etc. without any effect really.

Last weekend I make a little "experiment" but results are kinda strange. I disconnected all tubes from engine head (I have 3: breather to the air intake tube, PCV to the throttle and crankcase vent. tube). While engine is idle I detected direction of air and surprise, air went _out_ from all openings in the valve cover!

That I do not understand. My understanding that excess of gases in upper engine comes from crankcase (by ventilation hose). But it is not true for my engine. So, what the source of air pressure then? Valves? Stacked exhaust?

BTW: Cylinder's compression is OK

So, I'm little lost now. Any ideas? Is it work as it should?

[MMamdouh]

post pics of the tubes you disconnected on that engine of yours... i recon the 2.0 engine got a couple of breather hoses if it is anything like the 2.0 found in a nubira

and BTW it is normal to see gases going out of the breather ports.

MMamdouh

[vit]

Yes, it T20SED, I believe the same for Nubira/Leganza?

Here what I disconnected; Arrows shows direction of the flow at all six opennings:

[MMamdouh]

the two hoses near the intake are the breather hoses... big one id prior to the TB and small one is next to the TB to ventilate gases when the throttle is fully closed

the front hose is a return hose for oil to drain from head to the pan... ever thought how does oil go from the oil fill cap to the pan?? it is through this hose to the metal pipe going down to the pan

removing any of them hoses will induce vapors to come out so it is normal

MMamdouh

[Trey05Woo]

Yea the ventilation system in daewoos is the always blow through design similar to cars in the 50s except due to new emission regulations you can no longer run a breather pipe out the engine block into the atmosphere. The system works in reverse as described above though. Crankcase gases vent from the metal pipe into the valve cover. The system has two vacuum connects one before throttle (bypassed at idle) and one after throttle (bypassed when engine speed increases and vacuum drops). Its very difficult for this system to build an obstruction but if there was one, the only place it would develop it is the valve cover. You can check this by disconnecting the hoses which connect at the three ports of the valve cover and suck/blow air into each each one with the engine off. You should experience no resistanceAir should blow through the valve cover with ease.

With the system disconnect the ONLY place you should feel significant blow-by is from the big tube at the front left of the engine. The metal pipe which come out of the block. this is the pipe that feeds the crank gases into the valve cover and recycles it back into the engine. If you feel significant blow-by coming from the the valve cover ports with the main feed hose disconnected from the crank pipe then the engine compression rings are worn and causing excessive blow-by. have you ever experienced oil spilling out of the dipstick tube?

In honesty i bypassed the system entirely. I bought one of them breather filters from the auto parts store and just plugged it directly to the vent pipe (coming out the engine block left front of engine) bought some vacuum plugs and plugged both ports on the intake manifold and the air duct (so dirty air wont bypass the filter). Ever wonder why IACs go bad and TB's get sticky and build crud? All that crankcase air which is fed back into the engine which should be ventilated out, but the government says destroys our environment. Keep in mind if you perform the above your car will not pass emissions. Buuut its only a couple hoses away from passing.

[vit]

If you feel significant blow-by coming from the the valve cover ports with the main feed hose disconnected from the crank pipe then the engine compression rings are worn and causing excessive blow-by. have you ever experienced oil spilling out of the dipstick tube?

I'm not. But I own car about half a year...
So how these blow-by's can get from valve cover with big tube disconnected? By using oil galleries or whatsoever?
The engine has good compression...

Ever wonder why IACs go bad and TB's get sticky and build crud? All that crankcase air which is fed back into the engine which should be ventilated out, but the government says destroys our environment.

Yea, I've cleaned TB the other day

[Trey05Woo]

Yea the head is not completely sealed off from the block. When you pour oil into the valve cover it finds its way into the crankcase via ports and orificies. Its normal for some compression to escape down into the crankcase as rings do not make a perfect seal. In the 2.0l the gases vent mainly from the tube up left front, if you take a rag and cover this tube with the engine running you will see a significant increase in blow by from the valve cover ports and even the dipstick tube. the engine might even stumble or stall because you are choking it.

even if the engine builds good compression it could still have worn rings. the correct test to perform is a cylinder leakdown test and a vacuum test.

visual signs to check for are high oil accumulation at the throttle body valve and air duct, and all hoses. high oil consumption due to the above, heavy smell of emissions with the engine running and the system connected and sealed, and the engine burning oil due to oil making its way inside the intake manifold.

the systems pcv valve is the valve cover itself. when the crankcase gasses are pushed into the cover via pipe, the engine sucks gases through the valve cover via which ever port depending on idle or open throttle. the valve cover filters some oil out, but with excessive blow by oil will run through.

if you are experiencing any of the above i would perform a cylinder leak down test, and if worn rings are determined just put a filter directlly on the breather tube and by pass the valve cover and tb directly.

[vit]

Thanks Trey05Woo for the explanation. Tried to disconnect "left-front" tube again. What bothers me that the air flow from the head is almost the same as from crankcase tube. Moreover, it contains drips of oil, so if I place a napkin in front of it it becomes wet in oil in a couple of seconds!
How the oil pump should work? Is it possible for it to grab some "air" with an oil while pumping it to the upper side of an engine? Do I have a "crazy" pump with huge productivity?
Is it worth to try to unscrew oil dipstick and bypass tube holder? I don't believe that tube of such diameter may stuck with something but who knows?

[Trey05Woo]

well you said yourself the car is a poor serviced 100k + mile vehicle. most probably the previous owners did not perform timely oil changes hence abnormal engine wear and the excessive blow-by.
due to the higher than normal blow-by however, you need to compensate the stock ventilation system to allow the engine to vent these extra gasses. the method i mentioned earlier will help contain some of the oil. keep in mind you should check the oil daily, and after extended periods of use.

the oil pump has nothing to do with blow by, all it does is simply move oil from the crankcase through the crankshaft, rods, pistons, cam shaft, head, and back via galleries, and orfices.

blow-by is caused by compression escaping past the piston compression rings when the piston comes up on it's compression stroke. this escaped compression enters the crankcase (oil pan) and looks for the path of least resistance to exit. as i said some blow-by is normal because no ring seals perfectly in a cylinder, but when you have worn or damaged rings, more than normal compression will leak down into the oil pan and pressurizes it, this will push oil out as gasses vent. think of it like putting a hose into a bucket of water and blowing through it.

anyways glad i could help you understand. just put a blow through filter on the pipe plug the tb port and check the oil lvl regularly. ive seen engines with blow-by run thousands of miles with upkeep...