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Discussion Starter #1
Hey guys I’m pretty sure I seen a discussion about drilling out the pcv a little to help with oil consumption?? I looked and searched and can’t find it. Like lots of 3.6 owners I’m using a couple quarts oil per 5k oil change. Maybe I’m crazy? Is the catch can the best solution??? Can someone send me the link if one is out there..


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Re: Pvc mod

Be very careful with how you interpret that video and the PCV modification.

First, his opinion is that a valve cover ventilation issue on the passenger side causes what appears to be oil sludging that can lead to oil starvation if the oil pickup is obstructed by it. The motor also does not appear to have been using full synthetic oil. He addresses oil quality and oil change intervals as well, which contribute to the build up shown in the video. I agree that poor ventilation causes a greater amount of tinting on the passenger side.

Note that the demo motor has a roller style chain which means it is early 2007, or older. GM switched to the silent non roller chain around 07.

I understand GM, or just Mahle and Felpro modified the passenger side valve cover gasket which is closed off at the rear end except for a small hole for each of the three passages, unlike the older open design seen in the video.

If you have an oil usage problem, I believe the PCV modification will make it worse. Here's why, there are three locations for the oil to enter the engine; the PCV valve to intake, the driver side vent tube to air inlet tube, and past the piston rings.

If you open the PCV passages, instead of just replacing it as routine maintenance which it is designed for, you will increase air flow to the intake plenum and along with that, the amount of oil mist. An oil catch can will reduce or prevent the oil flow to the intake, but you'll still be pulling it into the can and you don't want that either. The air flows through the motor in both directions, it can reverse into the intake air tube from the driver side valve cover at heavy throttle input when intake vacuum is low and crankcase pressures are high from combustion gasses.

I performed the PCV modification after an oil change while at my Mom's house. I made all of the holes the same size. I drove the 80 mile trip home. I checked my oil level and if I recall correctly, it was a 1/2 quart low and that frightened me, because my motor does not use oil that I've been able to detect on the dip stick between change intervals. I replaced the modified PCV valve immediately with a new stock part and haven't had that problem since. I'm confident that if I had drilled the holes in accordance with the recommendation, the motor would still have pulled more oil into the intake, just not as much and that still makes the modification a no go for me.

When I replaced my timing chains at 175k miles, my engine did not look like the one in the video. It was pretty clean although there was more tinting on the passenger side.

Like so many who have installed an oil catch can, you'll need to empty it and probably possibly more frequently because of the modification, but what you need to do is keep more of those two quarts in the motor. You'll need to investigate where you're losing oil, through the intake, or past the piston rings. If you remove the PCV valve, yous should be able to look through the hole and see if you have the updated gasket in place, if not that may help. I attached a picture of what the newer design looks like. The old style is still available so it can end up on a newer motor by someone unaware.
 

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Discussion Starter #5
Pvc mod

Be very careful with how you interpret that video and the PCV modification.

First, his opinion is that a valve cover ventilation issue on the passenger side causes what appears to be oil sludging that can lead to oil starvation if the oil pickup is obstructed by it. The motor also does not appear to have been using full synthetic oil. He addresses oil quality and oil change intervals as well, which contribute to the build up shown in the video. I agree that poor ventilation causes a greater amount of tinting on the passenger side.

Note that the demo motor has a roller style chain which means it is early 2007, or older. GM switched to the silent non roller chain around 07.

I understand GM, or just Mahle and Felpro modified the passenger side valve cover gasket which is closed off at the rear end except for a small hole for each of the three passages, unlike the older open design seen in the video.

If you have an oil usage problem, I believe the PCV modification will make it worse. Here's why, there are three locations for the oil to enter the engine; the PCV valve to intake, the driver side vent tube to air inlet tube, and past the piston rings.

If you open the PCV passages, instead of just replacing it as routine maintenance which it is designed for, you will increase air flow to the intake plenum and along with that, the amount of oil mist. An oil catch can will reduce or prevent the oil flow to the intake, but you'll still be pulling it into the can and you don't want that either. The air flows through the motor in both directions, it can reverse into the intake air tube from the driver side valve cover at heavy throttle input when intake vacuum is low and crankcase pressures are high from combustion gasses.

I performed the PCV modification after an oil change while at my Mom's house. I made all of the holes the same size. I drove the 80 mile trip home. I checked my oil level and if I recall correctly, it was a 1/2 quart low and that frightened me, because my motor does not use oil that I've been able to detect on the dip stick between change intervals. I replaced the modified PCV valve immediately with a new stock part and haven't had that problem since. I'm confident that if I had drilled the holes in accordance with the recommendation, the motor would still have pulled more oil into the intake, just not as much and that still makes the modification a no go for me.

When I replaced my timing chains at 175k miles, my engine did not look like the one in the video. It was pretty clean although there was more tinting on the passenger side.

Like so many who have installed an oil catch can, you'll need to empty it and probably possibly more frequently because of the modification, but what you need to do is keep more of those two quarts in the motor. You'll need to investigate where you're losing oil, through the intake, or past the piston rings. If you remove the PCV valve, yous should be able to look through the hole and see if you have the updated gasket in place, if not that may help. I attached a picture of what the newer design looks like. The old style is still available so it can end up on a newer motor by someone unaware.
OK so I might go ahead and buy the new PCVand also do the MOD just to maybe get some kind of comparison. Now that I think about it I may have actually ordered and replaced the PCV, I have to pull up my rock auto orders. And did you watch the YouTube video with the 7/64s and the 5/64 Holes? I didn’t know if you believe that to be an accurate drill bit size. My car has 101,000 on it it’s a 2010 CTS Awd 3.6. I’ve never seen any smoke out of the tailpipe‘s or any funny smell. So I’m not sure how much blow by I would be getting past the rings. Although I did clean the throttlebody this evening and replaced the gasket and I did have what I would say was three or 4 tablespoons of oil in the intake. And on a sidenote the AC Delco replacement throttlebody gasket does it matter which way it goes on it has a concave Ring I would say that goes around it I’ve made that face towards the intake although I can’t see it making a difference. I think I will try amp draw that out today clean it up real good and see what happens. Thanks for the good info. Also I have all the parts timing chain and gaskets to do the timing chains we just haven’t got around to doing it yet also have all the fluids and gaskets to do both differentials and transfer case and transmission.




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Discussion Starter #6
Re: Pvc mod

Upon further review I bought all new PCV stuff. And the hose too I guess. SoI will take the valve up and see with the holes look like you figured after all this time that would’ve shipped all the new PCV with a little bit bigger hole in them.



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Re: Pvc mod

I wouldn't modify the PCV at all, if GM hasn't done it by now it is with good reason. All it will do is allow more air and oil into the intake. The throttle body will need to close more to counter the increase in air flow through the PCV in order to maintain the desired idle, not an issue but an indication that the PCV openings are part of the idle rpm equation. Since you have an oil consumption history, I would not risk the PCV modification. I've read a few stories on strange and sudden high oil consumption resulting in engine damage all associated with the CTS. GM refers to your level of oil consumption as normal, but I would never be okay with that, I've never owned a car that consumed oil at that level, not even on conventional oil and regular abuse. The throttle body gasket install shouldn't matter, but I would install it with the raised portion facing the throttle body.

When you install the timing chains, make sure you physically push the tensioners outward and then press inward on them to make sure they are fully extended and locked into place. On first start up after the job is complete, perform a clear flood crank (gas pedal to the floor while engine is cranked), that will keep the motor from starting while at the same time pumping oil through it so that you avoid a dry start and have to listen to a lot of scary "I think I messed something up" noises until the oil system is pressurized.
 

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As to the PCV mod, It is my understanding that increasing the size of the orifice in effect lowers the velocity of the air stream thereby lowering the amount of oil the air stream can pick up. Ideally you want to pick up vapor and not oil droplets. Increasing the volume does not hurt if the velocity is lower.
I had installed my catch can a year or two before I did the hole size modification, after the mod the amount of oil caught in the can was significantly reduced and in my mind validating the theory.
 

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As to the PCV mod, It is my understanding that increasing the size of the orifice in effect lowers the velocity of the air stream thereby lowering the amount of oil the air stream can pick up. Ideally you want to pick up vapor and not oil droplets. Increasing the volume does not hurt if the velocity is lower.
I had installed my catch can a year or two before I did the hole size modification, after the mod the amount of oil caught in the can was significantly reduced and in my mind validating the theory.
I can only speak for my experience where the only modification was opening the PCV valve holes after a routine oil change and the immediate result was oil consumption where before I had none, that immediately resolved with a stock replacement. I can't see how making the holes larger would help the situation by allowing more air volume. The reduced velocity theory is relative, if in fact it is real, with the modification, the airflow velocity through the PCV orifice is pretty high regardless considering six cylinders are taking turns trying to pull their volume through it with the throttle body nearly closed.

2 qts per oil change interval, I'd be very careful. The modification didn't work for me and I only tried it to circulate more air through the motor.
 

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I tried the PCV modification as well. Mine used oil both before and after modification. My experience was that the mod caused oil to settle onto the piston heads causing a puff of smoke on cold startup (occasionally but not every start). I also experienced occasional misfire codes. I switched back to the OEM PCV stem and the car went back to sucking the oil through the intake (I know because I can see some in the tube that taps into the air intake tube). There it is burned gradually in the combustion process. I have non-DI so not as worried about carbon buildup on the valves as they are constantly cleaned by the fuel spray.
 

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Because the PCV system does, by design, move a significant volume of air through the engine valvetrain and crankcase it WILL carry off some oil vapor as well as acids and moisture boiled off by engine/oil heat. That oil consumption is calculated into the engine design specifications statements.

A catch can lets you dump the insignificant amounts of condensed oil instead of the engine burning it (along with the acid and moisture vapor which does not stay in a catch can).

An old Northstar trick was to carry the engine oil a half quart low so the crankshaft rotating assembly tended to whip less oil into foam/vapor.

That's no solace for a DI engine, though. The intake valve tulips will - will - get filthy. The actual effect of that is subject to discussion.
 

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There is a posting from a guy that is involved with I believe overkill that goes into the reason behind modifying the PCV "valve". And his suggestion is that GM DID actually open up the holes in newer vehicles. It has to do more with WOT if I recall. At WOT the pressure built up causes the air flow to instead of going through the passenger side "dirty" system, go through the "clean" system on the drivers side which puts oil directly into the intake tube.

I wrote to him that I noticed no difference in my car when I drilled out the holes to the specified sizes (he has specific sizes to drill them out to... Too big and it defeats the purpose). He suggested that I needed to also install a catch can because apparently there is some valving within the engine for the pcv system that get gunked up and need time to clear up. Apparently with the LFX engines they fixed this issue... Not sure which year. It may have been sometime during the 2012 model year.

My 2012 looses NO oil between oil changes which is kinda nice since my '09 burned a quart every tank of gas. I will be installing catch cans in my car at some point.. I have one sitting here waiting for me to figure out the best place to install it.

Rodney
 

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Discussion Starter #13
Re: Pvc mod

Be very careful with how you interpret that video and the PCV modification.

First, his opinion is that a valve cover ventilation issue on the passenger side causes what appears to be oil sludging that can lead to oil starvation if the oil pickup is obstructed by it. The motor also does not appear to have been using full synthetic oil. He addresses oil quality and oil change intervals as well, which contribute to the build up shown in the video. I agree that poor ventilation causes a greater amount of tinting on the passenger side.

Note that the demo motor has a roller style chain which means it is early 2007, or older. GM switched to the silent non roller chain around 07.

I understand GM, or just Mahle and Felpro modified the passenger side valve cover gasket which is closed off at the rear end except for a small hole for each of the three passages, unlike the older open design seen in the video.

If you have an oil usage problem, I believe the PCV modification will make it worse. Here's why, there are three locations for the oil to enter the engine; the PCV valve to intake, the driver side vent tube to air inlet tube, and past the piston rings.

If you open the PCV passages, instead of just replacing it as routine maintenance which it is designed for, you will increase air flow to the intake plenum and along with that, the amount of oil mist. An oil catch can will reduce or prevent the oil flow to the intake, but you'll still be pulling it into the can and you don't want that either. The air flows through the motor in both directions, it can reverse into the intake air tube from the driver side valve cover at heavy throttle input when intake vacuum is low and crankcase pressures are high from combustion gasses.

I performed the PCV modification after an oil change while at my Mom's house. I made all of the holes the same size. I drove the 80 mile trip home. I checked my oil level and if I recall correctly, it was a 1/2 quart low and that frightened me, because my motor does not use oil that I've been able to detect on the dip stick between change intervals. I replaced the modified PCV valve immediately with a new stock part and haven't had that problem since. I'm confident that if I had drilled the holes in accordance with the recommendation, the motor would still have pulled more oil into the intake, just not as much and that still makes the modification a no go for me.

When I replaced my timing chains at 175k miles, my engine did not look like the one in the video. It was pretty clean although there was more tinting on the passenger side.

Like so many who have installed an oil catch can, you'll need to empty it and probably possibly more frequently because of the modification, but what you need to do is keep more of those two quarts in the motor. You'll need to investigate where you're losing oil, through the intake, or past the piston rings. If you remove the PCV valve, yous should be able to look through the hole and see if you have the updated gasket in place, if not that may help. I attached a picture of what the newer design looks like. The old style is still available so it can end up on a newer motor by someone unaware.


So like I said before I have everything to replace the timing chain. My friend is a GM tech and he’s the one actually doing the work. So he’s telling me it’s actually the left side cover that cures the problem. He said he would send me the part number and the bulletin when he gets to work tomorrow. Was going to wait a month or two to do the timing chains but might go ahead and do it sooner than later.



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There is a posting from a guy that is involved with I believe overkill that goes into the reason behind modifying the PCV "valve". And his suggestion is that GM DID actually open up the holes in newer vehicles. It has to do more with WOT if I recall. At WOT the pressure built up causes the air flow to instead of going through the passenger side "dirty" system, go through the "clean" system on the drivers side which puts oil directly into the intake tube.

I wrote to him that I noticed no difference in my car when I drilled out the holes to the specified sizes (he has specific sizes to drill them out to... Too big and it defeats the purpose). He suggested that I needed to also install a catch can because apparently there is some valving within the engine for the pcv system that get gunked up and need time to clear up. Apparently with the LFX engines they fixed this issue... Not sure which year. It may have been sometime during the 2012 model year.

My 2012 looses NO oil between oil changes which is kinda nice since my '09 burned a quart every tank of gas. I will be installing catch cans in my car at some point.. I have one sitting here waiting for me to figure out the best place to install it.

Rodney
That's correct, the air flow does reverse direction when the engine speed is high enough not only because of an increase in crankcase pressure, but because the vacuum pressure of the intake decreases as the throttle is opened and the larger unrestricted passage on the driver side becomes a better path for air flow. The driver side has a baffle to help out but oil enters the engine from both sides and if you look closely at the air intake tube you'll note that there is a section molded into it that appears to be a reservoir to catch and hold some of it. Some models have a small plastic tank attached to the intake tube that can serve in that capacity although from what I read years ago it may serve the purpose of reducing airflow noise (usually found on the CTS4). I've seen intake tubes from other GM vehicles with a similar attachment and they all look like reservoirs and some contain a large quantity of oil if turned on end.

The LFX is not much different and you'll find some are fitting it with an oil catch can as well.
 
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