8.1L 496 internal closed pcv modification advice

[1 FMF]

here are pics of intake manifold off my sierra 2500, engine is 8.1L. This has the closed or interal pcv system, requires no maintenance. I did some researching and there are complaints of 8.1L burning oil, whether or not it's due to the pcv system i don't know. But i'm wondering if i should block this off and set up a traditional external pcv system. The whole inside of my intake is coated in a brown oil varnish, i don't know if that's normal. I recently bought this truck, haven't put more than 1000 miles on it before jack standing it to fix an exhaust leak. so i really don't know if it's an oil burner. I've been going to town on everything under the hood to fix things right and for the last time... have injectors getting cleaned and hope to get more than 11 mpg when finally finished. But i don't want to put the intake back on and later have to pull it again, gaskets are $70. I also had what looks like ash deposits on the spark plugs, they were not oil fouled and were clean and whitish. so i don't know if that might have been previous owner using fuel additives, will post pics of spark plugs when i can

http://www.gm-trucks.com/forums/index.php?showtopic=90812

 

[AVB]

What do the intake ports in the head and the valve stems look like? I had a 6.0 a while back that had what looked like bbq sauce burnt on a grill rack looks like on the valve stems, and the ports were a gooey sticky mess. I think it was just due to the poor quality fuel the government buys. This was on a low mileage 2005 c2500 GSA truck it also had a worn out cam lobe and scoring on the #2 cylinder.

 

[NHGUY]

Dont expect much mileage.Everybody that has one that big says they are hogs.The 6.0 is bad enough on gas.

 

[SteveSRT8]

Hopefully no one is dumb enough to buy one of these monsters and expect good mileage! Ha, that's a joke, right?

Use Kreen on this issue. It goes in the oil and the gas and cleans all this stuff up. Make sure the thermostat is factory hot, and watch the metered pcv carefully as it can contribute to some of the ills listed here.

BTW, I have 6.0's in my fleet that weigh as much as two vans and still can get excellent mileage, 16+. Not bad for an extended wheelbase van loaded to the gills!

 

[1 FMF]

this does not have a pcv valve. It is not metered.
Well it is, in the sense that the air hole opening is only 1/4" in the throttle body which flows clean air into the crankcase. Then there is the 1/4" tube in the bottom of the intake manifold which I believe crankcase air flows right up into the intake plenum and into the cylinders. so it's however much air, and oil, can flow through a hole with a diameter of about 1/4".

 

[artificialist]

The GM Ecotec uses this sort of manifold, and they aren't known for oiling problems.

However, the Jeep 4.0 uses a metered CCV system, and I have seen more of them leak than I can remember.

 

[1 FMF]

here's what i am thinking, all air is metered by the MAF sensor. The sequence is air filter box with MAF sensor mounted directly off it, then piece of hard tubing going to the throttle body mounted on the intake. In the upper corner of the throttle body is a 1/4" passageway which lets fresh filtered & MAF metered air directly into the crankcase below the intake manifold. If you look at my pic above, you'll see the small tube on the underside of the intake. This goes directly into the intake plenum and is the same size as the hole in the throttle body. The air flows into the crankcase under the intake manifold, then is sucked back into the intake plenum by that tube in the pic above. Given the way this ventilation system is set up that means the crankcase can have no leaks anywhere otherwise this ventilation system will also suck air in from there which is then not MAF metered air and is a vacuum leak. Having looked over everything these are what could now be vacuum leaks: the oil dipstick tube into the block and the dipstick itself not seated, the oil fill cap, gaskets including oil pan gasket and valve cover gasket.

what i'm thinking of doing is blocking off that tube on the underside of the intake. then i was thinking of putting a 1/4" fitting into each valve cover and running pcv hose or vacuum tubing to somewhere into the intake plenum behind the throttle body. provided there are no vacuum leaks anywhere else on the motor all the pcv air is metered by that 1/4" hole in the throttle body. before i start drilling, what am i missing?
reason for doing this would be to prevent any oil being sucked up by that tube in the underside of the intake manifold.