6.6 - Catch Can - Final Answer

[mrjulian416]

The passenger side tube is the "fresh air" line allowing clean, metered air a path into/out of the engine.  It is not a "foul air" line letting blowby out of the engine.  There is much higher vacuum after the throttle plate than inside the resonator box.  It might be interesting to see what you catch in a can on that line, but I'd be surprised if it's the same stuff as you catch on the driver's side tube.

 

Can makers are always happy to show the pics of X tablespoons of nasty liquid collected in Y miles.  But there is never any indication of how many MORE tablespoons of stuff weren't captured in those Y miles.  Does a can have an effect on what gets sucked back into the intake?  Yes.  Does it have a meaningful effect? Ehhhh.....

 

As far as engineering/science based insight into the need/effectiveness of catch cans, this technical research summary is a very interesting read.

 

Considerations on Carbon Deposit Formation in Gasoline Direct Injection Engine

 

The conclusions of the study basically indicate:

• intake valve carbon deposit formation is worse under lighter load than heavy (counterintuitive to blowby being a primary cause)
• it is not related to blowby gasses in the intake (ah hah!, which as part of the testing were completely blocked off from entering the intake)
• indications are oil degradation is contributing, potentially due to effects in the combustion chamber, which at light load can and will see chamber gasses circulate back out of and into open valves during an intake cycle (reversion)

In other words, catch cans don't help.  Instead change your synthetic oil frequently.

 

But if adding a can helps you sleep better, then by all means.  Or add two.  The presence of a few tablespoons of nasty looking liquid in Y miles doesn't mean that liquid was your only problem.

 

Aaannnnddd.... whether GDI or MPFI, makes no difference to what flows through the PCV breather tubes.  You'll see the same stuff in a can on either type of engine.

Edited March 29 by mrjulian416
added GDI vs MPFI bit

[C/K Man]

That's good information, but there is another factor.  Late model engine with variable valve timing open the intake valve before the piston reaches TDC on the exhaust stroke.  This is done to recirculate exhaust gases (EGR) back in the combustion chamber without using an EGR valve like older engines did.  Those exhaust gases are blown up into the intake port momentarily before the piston goes past TDC and starts down on the intake stroke, which draws the exhaust gases back into the cylinder along with the incoming intake charge.  The exhaust gases are hotter than the back side of the intake valve and the surrounding intake port, so they tend to condense on those surfaces eventually leading to deposits if excessive.  That is why when you see intake valve/port deposits on an engine the deposits are seldom more than an inch or so above the valve, the exhaust gases don't have a chance to migrate very far up the intake port before being drawn back into the engine.  While it is true crankcase ventilation (and leaky intake valve guides) can contribute to intake valve/port deposits , most all of what you see these days is from the EGR effect of variable valve timing.  Of course, port type fuel injection (and quality gasoline) did a great job of keeping the intake clean, and with GDI alone we don't have that 'luxury' anymore.  A 'catch can' may reduce intake deposits slightly, but the best way to keep the deposits to a minimum in a GDI engine is with good quality gasoline, the proper synthetic motor oil, and good maintenance. 

 

FWIW I have a friend with a GDI 3.6 2013 Impala with over 200,000 miles on it.  No issues with excessive deposits.

 

I wonder about using E85 in GDI engines.  E85 capability is still an option on some Silverado/Sierra HD's with the L8T.  I have seen engines run on E85 for many miles with almost no carbon deposits in the combustion chambers, if you are not making the deposits in the cylinder I don't see how you would have any in the intake port.    

[mrjulian416]

C/K Man

 

Exactly right... which is why a catch can is really a psychological improvement to valve deposits and not really an empirical one.  High quality gas, and frequent oil changes is the answer.  Not a can that collects mostly water vapor and mixes it with a little oil.

[lineman1234]

Me,,,, im just hear to post MY, facts, conditions. Not to debate is the world round or flat on the motor world. 

.... 

I have never used one, a catch can till i put one on this 2024 L8T. IT, seems to be pulling some water and a little oil vapor out of the system. Does in need to, NO, will it hurt, ill find out if something happens. 

... The last dump is the pic of about 140 miles all highway, the can is/was almost half full. 

... Fuel is gotten from a local Cenex station, 10% ethanol, as its hard to find non ethanol hear in the Midwest. It is going to warm up from the 20s and 30s to 50 in a few days, so maybe temp plays a part, maybe not. 

[lineman1234]

It just occurred to me, i didnt give my reason for said can. My experiment with said catch can, soon to be can's is not to worry about the dreaded intake and valves crudding up, like most use it for. 

... I was and am more interested in the results of less to non of the vapors of oil and water, let alone extra what ever the nasty smell is that is in that oily water, being put into the intake to be added to the EGR great stuff and mix with air, to help or is it hinder combustion. 

... So far, my fuel mileage, and the 6.6 gasser isnt made for fuel economy, its made to work. My fuel economy hasn't changed, by adding the first can. So the extra water vaper and oil vapor dont seem to change how the system makes power. VS without the water and oil vapors. 

... The motor purrs the same before and with the experiment. 

... Its an experiment. Thats all. I may remove it/them in the summer after i see what the warm temps do. I may leave them on to just see what water it/they have taken out of the system, so the system didnt need to burn it off. 

[Pryme]

4 hours ago, lineman1234 said:

Me,,,, im just hear to post MY, facts, conditions. Not to debate is the world round or flat on the motor world. 

.... 

I have never used one, a catch can till i put one on this 2024 L8T. IT, seems to be pulling some water and a little oil vapor out of the system. Does in need to, NO, will it hurt, ill find out if something happens. 

... The last dump is the pic of about 140 miles all highway, the can is/was almost half full. 

... Fuel is gotten from a local Cenex station, 10% ethanol, as its hard to find non ethanol hear in the Midwest. It is going to warm up from the 20s and 30s to 50 in a few days, so maybe temp plays a part, maybe not. 

So you would completely fill your can in about 300mi??? That makes no sense at all. The only person I knew who ran a catch can was a friend with a hot 4 banger turbo about 20 years ago and it would take a few thousand miles to get close to filled. 

[lineman1234]

Yep, that is what is seems like. Im not making this up.  I drive and empty, i know how many miles each empty. At this rate, it would be a full can, or more, per tank of fuel. 

.... If it cant go a can per tank, it needs a bigger can, or put back to normal.

... I need to find a station without ethanol or fill up with 91 to see if its the ethanol crap that is adding water to the system, that would  normally go down the throat unnoticed. 

[carkhz316]

15 hours ago, Pryme said:

So you would completely fill your can in about 300mi??? That makes no sense at all. The only person I knew who ran a catch can was a friend with a hot 4 banger turbo about 20 years ago and it would take a few thousand miles to get close to filled. 

Mine will achieve this as well. I'm in the midwest (Minnesota) and when its a high dewpoint in the winter combined with fluctuating cold temps and some short trips in and around town, it always does this on any of my vehicles. Theres going to be some differences in how the cans fill up that might not seem normal to you.

Edited March 30 by carkhz316

[carkhz316]

13 hours ago, lineman1234 said:

Yep, that is what is seems like. Im not making this up.  I drive and empty, i know how many miles each empty. At this rate, it would be a full can, or more, per tank of fuel. 

.... If it cant go a can per tank, it needs a bigger can, or put back to normal.

... I need to find a station without ethanol or fill up with 91 to see if its the ethanol crap that is adding water to the system, that would  normally go down the throat unnoticed. 

This seems pretty normal to me. I'm in Minnesota and our family car (G8) will fill the can up in a couple weeks of varied driving in the winter. Contrast that with the summer and I might have to empty it once. Some people may not realize that different driving conditions and weather will affect how these systems behave. 

[customboss]

On 2/18/2021 at 12:44 PM, 6.6HD said:

Catch can is much like a Oil/Water separator. 

 

A catch can is only relevant for a DI engine.  There is so much info out there... do a bit of googling for more info. 

It's actually a fuel separator, separating unburnt fuel from crankcase PCV system, it captures raw fuel and post EGR fuel species.  It does mix with oil vapor but the majority of the volume of liquid is fuel. If one burns most of the fuel off the first run through a gasoline engine you WON'T HAVE measureable volume of liquid to capture.  As far as water vapor there is some that mixes in the catch can from incomplete combustion.  

 

Your damaged/defective injector was the cause of the incomplete combustion.  In even brand new DI engines with more than 10,000 miles of use causes  can be overused and restricted air filter, running untreated fuels that allow deposits to form on plugs, valves, rings, injectors, ( BTW 10-15% ethanol is a good thing for cleanliness in a closed fuel system so water entrainment is not an issue), defective coils from factory and associated plugs will make deposits in 20,000 miles that will be noticeable but MIL system may not warn of it, and poor cylinder seal from FUEL dilution of ANY engine oil. 

 

 

 

 

[customboss]

On 3/29/2024 at 11:04 AM, C/K Man said:

That's good information, but there is another factor.  Late model engine with variable valve timing open the intake valve before the piston reaches TDC on the exhaust stroke.  This is done to recirculate exhaust gases (EGR) back in the combustion chamber without using an EGR valve like older engines did.  Those exhaust gases are blown up into the intake port momentarily before the piston goes past TDC and starts down on the intake stroke, which draws the exhaust gases back into the cylinder along with the incoming intake charge.  The exhaust gases are hotter than the back side of the intake valve and the surrounding intake port, so they tend to condense on those surfaces eventually leading to deposits if excessive.  That is why when you see intake valve/port deposits on an engine the deposits are seldom more than an inch or so above the valve, the exhaust gases don't have a chance to migrate very far up the intake port before being drawn back into the engine.  While it is true crankcase ventilation (and leaky intake valve guides) can contribute to intake valve/port deposits , most all of what you see these days is from the EGR effect of variable valve timing.  Of course, port type fuel injection (and quality gasoline) did a great job of keeping the intake clean, and with GDI alone we don't have that 'luxury' anymore.  A 'catch can' may reduce intake deposits slightly, but the best way to keep the deposits to a minimum in a GDI engine is with good quality gasoline, the proper synthetic motor oil, and good maintenance. 

 

FWIW I have a friend with a GDI 3.6 2013 Impala with over 200,000 miles on it.  No issues with excessive deposits.

 

I wonder about using E85 in GDI engines.  E85 capability is still an option on some Silverado/Sierra HD's with the L8T.  I have seen engines run on E85 for many miles with almost no carbon deposits in the combustion chambers, if you are not making the deposits in the cylinder I don't see how you would have any in the intake port.    

E85 loves modern engines and modern engines love it. You fuel density measurement will trigger a MIL code and over rich the system if its tuned from factory for E10-15 like most are but you'll operate fine. 

[lineman1234]

I am no chemical analyst. But. My eyeballs tell me the stuff i dump out of the can into a qt jug, and when the jug sits, the yellow stuff darkens to oily stuff, and water seems to be on the bottom. 

...

The second can set up came in early, today, instead of Monday. So tomorrow morning that will be getting installed on the passengers side between the valve cover and intake box. If anything, that is where crampy stuff would be getting into the intake, not from the other first installed can. 

[Grumpy Bear]

The Truth Behind Carbon Buildup | Team Valvoline (valvolineglobal.com)

[Black02Silverado]

It would be interesting to see a catch can that E85 was 100% used. 

[CRApex]

10 hours ago, Grumpy Bear said:

The Truth Behind Carbon Buildup | Team Valvoline (valvolineglobal.com)

So problem solved, Easy GDI service and modern engine full synthetic!