davanz

I am looking for an answer as to how an issue with direct injection engines is being addressed in th C7. First a little background.

Through the years I have known of oil catch cans being installed in the PCV system and I understand their purpose. I never installed one on my Corvette engines, (currently an 06 LS2), as I do not drive it in such a way as to think it is an issue. But a while back I bought a CTS for my wife and it has the 3.6 DI V6. Upon visiting some CTS forums, I learned of the following:
As we know the PCV system draws gases from the crankcase and directs them into the intake manifold for them to be burned off. In these gasses there will always be a certain amount of oil mist or vapors which enter the cylinders along with the fuel, going past the intake valve. On any engine which has the gasoline introduced into the system ahead of the valve, such as a carburetor or port/throttle body injection, the gasoline is constantly washing off the back side to the intake valve helping to clean it. On the contrary, in a direct injection system, only air is flowing over the back sie of the valve and the oil from the crankcase builds up there, is "cooked", and starts to form a carbon deposit resulting in more and more interference with the intake flow. I have seen pictures of the intake valves on these engines which showed a lot of buildup in a few miles. Check out some of the pictures on the Camaro forums.

Out of curiosity I pulled the intake manifold cover off of my wife's CTS, with only 10,000 miles and was amazed at the amount of oil standing in there. With a flashlight I could see the intake runners also oil soaked so I am concerned about what may be happening to the valves. The point of this explanation is to document that I do not believe this an unsubstantiated fear, but something truly needing addressed. I cleaned out the manifold as best as I could, intalled a catch can, and am considering doing some type of chemical cleaning of the intake system.

If you have stayed with me this far you know the question. What, if anything has GM done about this for the C7's direct injection engine. Do any of you have any information? I am heading to the NCM Bash tommorrow and hope that this question will come up in one of the sessions there.

JerriVette

The entire lt1 is designed to not have a carbon buildup on. Valves. My 45k mile cts with direct injection has been flawless.

Every oil change I use a bottle of techron and I use shell tier one gasoline.

Buy the c7 LT1 with confidence. If you do a search you will see all the details as to what GM did with the LT1 design to not have what porsche and Lexus had with regards to direct injection.

That's GMs specialty and why their research and development teams are the best in the world.

Specifically corner Paul koerner....aka the corvette mechanic and he will have your answer in personal detail. We do a podcast together and he is in bowling green with our producer rob haggard to tape the seminars.....

Tell them JB sent you!

Enjoy

Kappa

I wouldn't worry about it. GM is very good at addressing DI issues unlike some of the German automakers.

lt4obsesses

As I understand it, the LT1 incorporates seperators for the oil and crank gases in the valve covers. So that the gases going into the intake should be, for the most part, oil free. I don't know all the specifics on this system.

As far as maintaining a DI system, while adding fuel system cleaner is not going to prevent build up on the backside of the valve that much, perhaps a bi annual top end cleaner treatment will help. DI provides for improved efficiency as well as allowing for more power, but it does come with some additional maintainence.

Oh, and BTW, coming from my brother, a senior Cadillac Tech. Ignore the engine oil life monitor on VVT engines. Change the oil every 5000, and don't wait for the monitor to read 10% or even 30%. By this time, you will have consumed enough oil that a low oil condition can damage the valvetrain. Just a heads up if you didn't already know.

Magister Ludi

Excellent question; excellent responses. Learn something every day on this forum.
Thanks.

JerriVette

Something to consider even with oil life monitors.....most Americans NEVER CHECK OIL LEVELS BETWEEN OIL CHANGES....HENCE THE PROBLEM WITH LOW OIL LEVELS..

I suggest checking the oil level when not changing the oil as frequently.....

GM needs to follow what BMW did and get rid of the dip stick entirely and just add an oil level monitor.


Unfortunately 90 percent of Americans are too lazy to check oil levels with the dip stick...

Sad but unfortunate fact of self service gas stations too....

Years back gas station attendants asked to check the oil for the increase in average transaction .......and the cars used oil.....

Even with 3000 mile oil intervals...

lt4obsesses

Yeah, my brother tells me he gets these things in, and the monitor says 10%. The last oil change would be 10K miles and he would get at most, one quart out of the six quart pan. And they wonder why their engine is noisy.

Not to derail this thread on DI however, just making the point that new technology brings new systems to maintain, and that improper maintainence is usually at root cause of complaints about these systems. There is a huge difference between poor design and poor ownership, and unforunately design often takes the hit when the other is the problem.

davanz

lt4obsesses. Do you think the commmon condition of people running engines with low oil has any relationship with the numerous reports of stretched timing chains on the GM V6 engines. Car maintenance is an obsession/hobby with me. I change oil and filter on my vehicles every 5000 miles regardless of any monitor reading and I would not like having an engine with no dipstick I can use to check the level every few weeks. I know that may be overkill but thats just me and my hobby.
By the way I still have a 1997 Tahoe that I bought new which now has 292,000 miles that I use regularly and it now uses some oil between changes. It has never needed any major work, heads never off, etc. and I attribute much of that with my oil change regime and use of a high grade of oil and fuel through the years.

I'll probably never see that kind of mileage accumulation on my Corvettes but I just like treating the cars as if that were my goal. I look forward to learning a lot more about the C7 drivetrain.

Kappa

Oil life is a pretty contentious subject in most enthusiast circles.

I like to run my oil out to 7500-9000mi. BMW and Porsche say 15,000mi is fine and there are some guys who are running motors with 200K+ with those intervals. Then you still have people who swear by 3000mi even with synthetic.

I don't have any problems following GM's oil life monitor. It's usually pretty accurate. Pretty complex algorithms are built into it.

DREAMERAK

I believe Porsche has went back to 10,000 after some "problems" a 911 engine is about $25,000 a turbo about $45,000.

robvuk

Zymurgy

From the "Gen 5 Small Block Lubrication System" press release:

Dominic Toretto

"GM needs to follow what BMW did and get rid of the dip stick entirely and just add an oil level monitor.


Unfortunately 90 percent of Americans are too lazy to check oil levels with the dip stick..."

Not sure about the C6s or other Corvette gens but, on the C5 I had, the oil dipstick was worthless. Never read correct. I had to RELY on the Low Oil Level indicator.

Not to thread hijack, carry on, great reading here.

-Alex

JoesC5

That's odd. On my C5, I changed the oil, start it and check for leaks, shut it off and let it sit for awhile so the oil would drain from the upper engine back to the pan, and it would read full.

Same with my C6 Z06. Change the oil, fill with 10.5 qts of oil, check for leaks and let the oil warm up, shut it down, wait 5 minutes and check level, and it reads on full.

Same with my other two Corvettes and my Mercedes. Filling the engines with the specified amount of oil and the dip stick registers on the full mark.

Been that way since I was in high school some 50+ years ago, changing oil in my Mom's Esso gas station after school and the weekends. No telling how many thousands of cars I've changed the oil in.

Unless you had the wrong dipstick in your C5, you shouldn't have gotten a wrong oil level reading.

RC000E

I ask the powertrain engineer about this at the bash. Corvette racing used DI when they were in GT/GT1. This isn't new to anyone, so I wouldn't concern yourself with it.

In terms of gasolines combustion stability, the presence of oil in the combustion chamber effectively reduces the effective octane. As a builder of some very high HP forced induction cars over the past 15+ years, effective catch can systems, eliminating recirculation, was a priority of mine to combat knock/pre-ignition.

I will ask at the Bash and report back what kind of response I get.

steel_3d

On my C6 I need to re-check the dipstick two-three times to be sure of the reading. The oil is smeared in such strange ways on the dipstick, that sometimes you could convince yourself of a reading on the high or the low end that are half an inch apart. Horrible design.

My wife's Audi TT is a much better design, with a double kink in the stick that protects the important reading range from smearing.

GOLD72

In the past several years I too have found oil smearing on the dipstick to be a problem on a number of cars which seems to be resolvable only by multiple checks and closely looking at the dipstick to see where the smear begins to gauge true level. PITA.

JudgeNjury

The people who don't check the oil between extended synthetic oil changes are clearly the problem.

That's why an oil level monitor system with an indicator on the dash makes the most sense.

Might be able to save a gram or two of weight if they get rid of the dipstick as well.

JoesC5

Can you explain why the wet sump Corvette engine has an oil level sensor, but the dry sump Corvette engine doesn't?