Instead of catch can, why not delete PCV?

Doublebase · August 26, 2019

I just emptied mine five minutes ago...should have taken a picture...half full (1,500 miles).

People praise this cheap $30 dollar can on Amazon...I can see why...for the money you can't beat it.

SquireSCA · August 26, 2019

How does GM not address this? I mean, how do they think dumping a full quart of oil into the intake manifold every 5k miles, isn’t gonna make problems?

SquireSCA · August 26, 2019

Also, unscrew the bottom from the top, and then unscrew the little baffle from the inside of the top. Stuff some stainless steel wool in there and then out the baffle back in, and then the bottom back on. That extra material will help filter the oil out of the air, forming larger drops that will fall into the baffle and settle out, and less being passed through to the vacuum line.

it won’t catch all, but removing 80-90% is well worth the $30...

Doublebase · August 26, 2019

6 minutes ago, SquireSCA said:

How does GM not address this? I mean, how do they think dumping a full quart of oil into the intake manifold every 5k miles, isn’t gonna make problems?

It is probably close to a quart of oil over 5,000 miles...and in the winter a good mix of condensation.

I haven't actually heard of any issues with carbon buildup on the valves on these engines, but it's got to be there. Can't be a good thing. And I shouldn't say that I've never heard of any problems, but just nowhere near as wide spread as early DI engines in the Audi's and BMW's. But yeah I'd prefer to catch it before it goes in that intake.

Grumpy Bear · August 26, 2019

33 minutes ago, Doublebase said:

It is probably close to a quart of oil over 5,000 miles...and in the winter a good mix of condensation.

I haven't actually heard of any issues with carbon buildup on the valves on these engines, but it's got to be there. Can't be a good thing. And I shouldn't say that I've never heard of any problems, but just nowhere near as wide spread as early DI engines in the Audi's and BMW's. But yeah I'd prefer to catch it before it goes in that intake.

Curious. How much oil do you use and what is your OCI? Thanks.

Grumpy Bear · August 26, 2019

SquireSCA. Your return line to the middle of the manifold. Where did that line originally source from?

SquireSCA · August 27, 2019

37 minutes ago, Grumpy Bear said:

SquireSCA. Your return line to the middle of the manifold. Where did that line originally source from?

I posted a pic, as well as a link to the install video. There is a line coming out of the top of the case, below the throttle body. That line ran from there to the intake. I checked to see which line was pulling the vacuum and it matched what the video instructions showed.

Doublebase · August 27, 2019

1 hour ago, Grumpy Bear said:

Curious. How much oil do you use and what is your OCI? Thanks.

I'm using about 3/4 a quart between oil changes. Has been that way since new.

My interval is 5,000 miles. Last three oil changes have been Pennzoil Platinum 0w20 (x2) and Rotella Gas Truck 0w20. I'm due for another soon, I'll probably try the Rotella again, as there is a rebate going on until the end of the year (it'll end up costing me around $2 a quart after the rebate).

Grumpy Bear · August 27, 2019

1 hour ago, Doublebase said:

I'm using about 3/4 a quart between oil changes. Has been that way since new.

My interval is 5,000 miles. Last three oil changes have been Pennzoil Platinum 0w20 (x2) and Rotella Gas Truck 0w20. I'm due for another soon, I'll probably try the Rotella again, as there is a rebate going on until the end of the year (it'll end up costing me around $2 a quart after the rebate).

So your losses are not from the crankcase to the combustion chamber up past the rings but rather from the crankcase into the intake manifold.

Doublebase · August 27, 2019

7 hours ago, Grumpy Bear said:

So your losses are not from the crankcase to the combustion chamber up past the rings but rather from the crankcase into the intake manifold.

I'd say that's probably mostly true because of the amount of oil being caught in the can, still there must be some blowby in that crankcase to push it up like that.

Like I said, it's been like this since it was new. Truck runs fine (35,000 miles now).

I work in the industry, I see a fair amount of these things pretty regularly. I usually pull the dipstick on all of them before an oil change to check for oil loss (out of curiosity). I've never seen a single one that wasn't down on that dipstick (5,000-6,000 mile intervals). The 2014's are the worst (at least from what I've seen)...we service one regularly and she can't keep the oil in it...uses a quart every 1,000 miles. But I'd say most are more like mine...1/2-3/4 quart of use over the OCI. I've talked to some Chevy techs, they say it's pretty normal - that these things do use some oil - but not nearly as much as the 2008-2013's

I'd also add that AFM failure is not nearly as widespread as people in the chat rooms claim. We service many of these trucks...mileage ranging from 30,000- 150,000. Haven't seen one failure yet. Talk to people at the dealer and they tell me it so not as frequent as people think. That more people complain of the switch from V4 to V8...how it feels etc, rather than lifter failure. There literally is over 3 million of these engines on the road right now, most people don't experience AFM failure.

Edited August 27, 2019 by Doublebase

SquireSCA · August 27, 2019

I think that there wouldn't be so much oil in there if there wasn't such a strong vacuum sucking it out of the crank case... Pull the dipstick on the catch can while the engine is idling and you will hear and feel how strong that suction is... I am betting that if you capped the vacuum line going to the manifold, and just put a pod filter on the "out" line on the catch can, the amount of oil caught would go down drastically. I don't think that the amount that is "pushing out" under crankcase pressure, is anywhere near as much as how much is being sucked out by that vacuum line...

Thoughts?

Edited August 27, 2019 by SquireSCA

Grumpy Bear · August 27, 2019

56 minutes ago, SquireSCA said:

I think that there wouldn't be so much oil in there if there wasn't such a strong vacuum sucking it out of the crank case... Pull the dipstick while the engine is idling and you will hear and feel how strong that suction is... I am betting that if you capped the vacuum line going to the manifold, and just put a pod filter on the "out" line on the catch can, the amount of oil caught would go down drastically. I don't think that the amount that is "pushing out" under crankcase pressure, is anywhere near as much as how much is being sucked out by that vacuum line...

Thoughts?

Well peak cylinder pressures are several thousand pounds. BMEP runs 120-190 psi. So some gas escapes past the rings. Except on the intake stroke the cylinder is always a positive pressure over the crankcase. If oil is getting into a cylinder it has to be on the suction stroke. To do that it has to get past the oil scraper and a pair of compression rings one of which is a reverse twist scraper. Given Doublebase's comment....sounds about on the money. It's being over scavenged.

That said on the V6 in my truck the vacuum to the manifold is from the rear of the driver's side valve cover and the vent, one, on the opposite head front to the airbox. The driver side cover has towers between the coils where baffles separate the oil from the gas and at the exit there is an orifice to control the amount of vacuum.

If I pull the drives side hose, it's damp if I run it hard but at my 5,000 mile OCI....she looses not a drop of oil.

Perhaps the answer isn't in eliminating all vacuum but in limiting it to SOME vacuum????

Edited August 27, 2019 by Grumpy Bear

SquireSCA · August 27, 2019

10 hours ago, Grumpy Bear said:

So your losses are not from the crankcase to the combustion chamber up past the rings but rather from the crankcase into the intake manifold.

Correct, and I am thinking that it's the massive suction from that line, from the intake manifold, that is drawing the oil out more than it being pushed out.

When I complete my 1,000 mile test with the catch can, I will see exactly how many mL of oil is in there. I will then take the vacuum line off of the catch can and plug it, and then put a pod filter on the "out" of the catch can, drive another 1,000 miles and see how much oil it captures and compare.

SquireSCA · August 27, 2019

6 minutes ago, Grumpy Bear said:

Well peak cylinder pressures are several thousand pounds. BMEP runs 120-190 psi. So some gas escapes past the rings. Except on the intake stroke the cylinder is always a positive pressure over the crankcase. If oil is getting into a cylinder it has to be on the suction stroke. To do that it has to get past the oil scraper and a pair of compression rings one of which is a reverse twist scraper. Given Doublebase's comment....sounds about on the money. It's being over scavenged.

That said on the V6 in my truck the vacuum to the manifold is from the rear of the drives side valve cover and the vent, one, on the opposite head front to the airbox. The driver side cover has towers between the coils where baffles separate the oil from the gas and at the exit there is an orifice to control the amount of vacuum.

If I pull the drives side hose, it's damp if I run it hard but at my 5,000 mile OCI....she looses not a drop of oil.

Perhaps the answer isn't in eliminating all vacuum but in limiting it to SOME vacuum????

That makes sense, but I am not an automotive mechanic, just a mechanically minded person, so I can't say for sure... but yeah, I think that a little vacuum would be fine, to draw a little pressure and vapor out, but it doesn't need to be so strong that it's literally sucking oil out of the case... I went literally 20 miles and there was a quarter teaspoon... That's insane. There is no reason or need for that.

Doublebase · August 27, 2019

10 hours ago, SquireSCA said:

I think that there wouldn't be so much oil in there if there wasn't such a strong vacuum sucking it out of the crank case... Pull the dipstick on the catch can while the engine is idling and you will hear and feel how strong that suction is... I am betting that if you capped the vacuum line going to the manifold, and just put a pod filter on the "out" line on the catch can, the amount of oil caught would go down drastically. I don't think that the amount that is "pushing out" under crankcase pressure, is anywhere near as much as how much is being sucked out by that vacuum line...

Thoughts?

Depends, I mean the engine vacuum seems pretty "normal" or in range to me compared to other engines I've seen. I think part of the problem might be air/oil separation through the PCV system...GM has neglected this in the past, only later to have to come back and correct it.

But oil tracking into the intake manifold does happen with lots of other manufacturers and engines. Owned a Lexus 460 for years...that intake always seemed to have oil in it...I'd even see it tracking through the fresh air portion of the PCV system, right up the air snorkel and into the throttle body.

Something maybe to consider with these engines is that manifold vacuum drops when it goes into V4 mode, that's the reason why the brake booster is not fed by manifold vacuum, but rather from a vacuum pump...because they couldn't chance drops in vacuum effecting braking. Now what I wonder is, when the switch from V4 to V8 mode occurs...might there be a vacuum "snap", a sudden uptick in vacuum that pulls in more oil initially?

Just a thought.