driving without PCV

[ukrkoz]

any ideas, how long can one drive a car with PCV disbled? purposefully, I mean.
I understand that it is supposed to ventilate crankcase. will simply PCV tube hanging loose do the trick? they used to have breather tubes in older cars...

I have reason. just curious.

[curtis73]

I discourage it highly. It seems like a worthless little $2 piece of metal, but it does more than just ventilate. Its a metered crankcase evacuation that does wonders for oil life. Without it, the oil can't effectively get rid of impurities. Old school breathers passively let evaporated contaminants escape, a PCV actively removes them. That's the "P" in PCV. "positive" as opposed to passive.

It makes healthy oil, which makes healthy engine.

[ukrkoz]

Originally Posted by curtis73

I discourage it highly. It seems like a worthless little $2 piece of metal, but it does more than just ventilate. Its a metered crankcase evacuation that does wonders for oil life. Without it, the oil can't effectively get rid of impurities. Old school breathers passively let evaporated contaminants escape, a PCV actively removes them. That's the "P" in PCV. "positive" as opposed to passive.

It makes healthy oil, which makes healthy engine.

a "hair club donor"??? there was nothing like "honorary mechanic" or some like that?

it is understood, not questioning value of PCV. so, basically, there will be slightly more retention of blow by gases in the crankcase, which should contaminate oil faster, which, with frequent oil changes, is a non issue?

i mean, common sense wise, right? i think, it is also known power mod, as it is believed that sucking gasses into the CC-s reduces engine power...

but this is not the reason i asked the question. our car fails CO emissions, based on "low O2 voltage at cruise speed due to excessive blow by gas recirculation through the PCV valve". hence the question.

[curtis73]

It is not a power mod at all. PCV only operates during idle and part throttle. At wide open throttle its not operating at all. Even if you just unplugged it and let it suck air, it wouldn't affect peak HP. Compared to the massive gulps of air that fit through the throttles, the tiny bit of flow through that 3/8" PCV tube has absolutely no effect on HP.

Emissions equipment is falsely accused of hurting power, but almost none of it does a single HP worth of damage. EGR only works at part throttle cruise, PCV isn't even an emissions piece, its just there for oil health, and smog pumps only take about 1/3rd hp to operate. The only real emissions piece that does directly affect HP is the catalyst, but since about 1990, catalysts have gone away from the dual-bed pellet type to the honeycomb matrix type and they are no longer generally considered a restriction. The use of emissions control devices occurred at the same time that two major things happened: 1) the auto industry switched from using gross HP to SAE net HP. The same engine that made 350 hp in 1969 only advertised 270 hp in 1972. Gross HP numbers are inflated and most companies just outright lied. 2) the government required massive reductions in emissions, so automakers responded by neutering performance. They didn't have the time to develop technology, so they just dropped compression ratios and used tiny cams. In 1969 you could get an engine with 11.5:1 compression off the showroom floor, but in 1976, some of them were as low as 7.2:1

PCV doesn't affect HP at all, and it is such a big help. Use one and change your oil every 5000 miles. Don't use one and change the sludge every 1000 miles and wonder why the inside of your engine looks like overcooked brownies. I wish I had a picture of the Isuzu I repaired last week. It had been operating without a PCV for a couple years, and not only did it blow the valve cover gaskets out, it was a nightmare under the covers. Imagine you poured brownie batter on top of the valve train, then cooked it until it was carbon. Everywhere something was moving, it had carved out a hole in the "brownies" to move, but there was no saving that. I did my best to not disturb any of it so it didn't fall down and clog the pickup, but that engine is on borrowed time.

Use a PCV. Pretty please.

[curtis73]

Originally Posted by ukrkoz

but this is not the reason i asked the question. our car fails CO emissions, based on "low O2 voltage at cruise speed due to excessive blow by gas recirculation through the PCV valve". hence the question.

What car and year?

Many things can cause that code, how did you determine it was PCV? Could be a malfunctioning EGR, could be bad cats, could be bad O2 sensors. Could also be a leaking injector, but typically you would fail from HC before CO.

[wrenchboss26]

i have seen cars with clogged pcv systems blow out oil seals, and oil pan gaskets. the vacuum created by the system can also aid the rings in sealing while the engine is cold. besides, an engine with any miles on it will likely blow some oil out of the tube and into the engine bay.

[ukrkoz]

Originally Posted by curtis73

What car and year?

Many things can cause that code, how did you determine it was PCV? Could be a malfunctioning EGR, could be bad cats, could be bad O2 sensors. Could also be a leaking injector, but typically you would fail from HC before CO.

Greg's Japanese Auto evaluation for "fail" emissions on CO level. They gave me spiel that though O2 is working properly, it is hanging at low voltage, 1V, at cruise speed, thus causing above mentioned condition, due to gasses blow by. It is 91 Civic, DPI engine.

She failed emissions on both NOX and CO march 31, before I bought her. As tabs were overdue, I could not really drive her. Simply having Seafoam in the tank, replacing gas tank cap, driving on Seafomed gas for about 100 miles, and CLEANING the throttle and area around it, whatever I could, made her pass NOX with flying colors, but CO was still failing. So, we had to apply for waiver, which involves spending at least $150 towards emissions related repairs, and that resulted in GJA conclusion.

Basically, we had to retest her yesterday, before waiver application, and CO went down even more - as I plugged PCV to prevent blow by of crankcase gases into the intake. Of course, if GJA's theory ir correct. otherwise, she tested 5 out of 5 on their testing equipment.

this car was neglacted by student owner. A lot of TLC will be done today. I have little doubt, as soon as I get timing right and replace leaking plug seals, she'll pass CO in a heartbit.

oh, and for the worried gentleman - I already have new PCV and will put it in today. old one was caked inside. black tar completely plugged it.

[MagicRat]

Originally Posted by ukrkoz

they used to have breather tubes in older cars...

Curtis is right on the money on this.

But another point. The breather tubes in old cars were not 'passive' either.
They were called 'road draft tubes'.

They were shaped and positioned in such a way that at speed, the air passing under the car created a slight negative pressure at the base of the tube. This actively sucked gases out of the crankcase, just as a PCV valve does.

The difference is the PCV valve obviously allows the gases to burn in the combustion chambers, reducing their polluting effects. The tubes simply dumped the pollutants straight into the air, which is a significant source of pollution.