I was fortunate and had no issues with my first oil change. When I scheduled it in advance, I asked and was told that it would be done by the Corvette tech. himself, not someone else.
I was able to go into the shop to meet and talk to the tech. who was very knowledgeable and professional, he explained that he had only put in 7.5 quarts and asked me if I wanted to take the other half quart with me. After meeting and talking with the Tech. I am very comfortable having my car serviced there in the future. The dealership is Ferman Chevrolet on North Dale Mabry in Tampa, FL.

 

Excessive oil can make its way to the intake.

Caused by excessive oil

 

^^^^
Originally Posted by C5racecar View Post
C8 has a dry sump oil system. That means that in theory there is little or no oil in the engine pan. There is no storage in the oil pan. The danger of overfilling was back in the old days when you were actually checking the oil storage level in the oil pan.
Too much oil could splash on the crankshaft causing oil foam. That was the old days. With a dry sump you are checking the oil level in the tank. The tank feeds the pump, nothing else. Do you worry if your windshield washer tank is overfilled?
Of course not, It is just a storage tank and it does not impact the performance of the pump. Same deal with the oil.

This is my understanding of dry sump systems from years of racing. Maybe the C8 is different, but dry sump means no oil storage in the pan. No oil starvation in high G corners and lower ground clearance is possible.
That's why SCCA TransAm cars have dry sumps and only 2.5" of ground clearance. The engine sits really low in the frame, and there is no room under the crankshaft for oil storage.
Excessive oil can make its way to the intake.

MY RESPONSE:
Yep but a race car dry sump is different!!
In a race car the scavenge pump pulls a lot of air along with the oil out of the crankcase. To get all the oil out it may have several scavenge pumps. (Note, that creates a partial vacuum that also helps increase power as the crack is spinning in a partial vacuum, less windage loss. In fact the C8 Z06 can achieve ~11 psi vacuum , i.e.only ~4 psi not 14.7 psi of air is in the crankcase so a significant help to reducing windage losses!) That crankcase air (with oil mist) in a race car is vented to the ambient air, no EPA rules.

With a passenger car dry sump EPA says, that air with some oil vapor is not just going into the ambient air! Have to make it go into the air intake. In the C7, if overfilled that meant a lot of oil not just oil vapor went into the air intake tube through the dry sump tank air vent hose! That went into the engine. NOT good. In some cases it just ran down the intake tube, soaked the air filter and dripped on the ground. Also not good.

The C8 has three oil/air scavenge pumps but the same issue. Can't just vent the large amount of air that comes from the scavenge pumps into the ambient air. In the C8 case don't know the path of how that air gets back to the intake but the EPA says it must be ingested!

 

The oil tank vents back to the rocker arm covers. In the illustration in post 11, it is the line (s) marked in red (line 2) that go from the oil tanks at point 1, and forks into two lines, on to each rocker arm cover (at points 5 and 10). The Service Manual says there is a centrifugal air/oil separator in the tank. That line is intended to carry the separated foul vapors from the oil tank back to the engine, where it eventually goes out line 6, marked in blue in the illustration in post 11, from another separator in the engine block valley (point 3) to the intake manifold at point 7, where it is ingested. And the manual is clear about not overfilling the tank. While it does not say why, if overfilled it would seem that oil would get sucked back through line 2, into the rocker arm covers.

 

^^^
Thanks Andy. Your explanation helps but a bit hard to see the pressure difference that causes the "foul air" as GM calls it from one side of the manifold to the other. I'm sure it does from the description but not clear how.
Made a pic for future reference:

 

Yes - While the engine block pressure fluctuates, I would assume that an average negative pressure is maintained due to the final PCV connection, line 6, that goes from the engine block valley to the intake manifold (the intake manifold vacuum providing the average negative pressure). The "centrifugal air oil separator" in the tank may also produce some positive pressure in line 2 but that is pure speculation on my part. I looked up "centrifugal air oil separator" and found a patent for it, and some generic examples, but I have no info specific to the C8 on how it works. Note that fresh air to system is provided by line 8, which draws its air from upstream of the throttle plate. Its in the above illustrations from the Service Manual. Here is an actual engine photo - the detail of the those connections my be more clear than in the Service Manual illustrations. I don't have a coupe, so its not easy for me to directly examine or photograph these lines and their connections.

 

Thinking about the C8 Z06 LT6 and the quoted operating with ~11 psi vacuum or ~4 psi versus 14.7 psi calculated the MPH.

Considering the LT6 can operate at 8500 rpm, that means the end of the counterweight and the rod big end are moving at ~135 mph. Lots of air drag that wastes hp. Much less drag and hp loss in 70% less dense air!

 

Mine was overfilled from the factory. No extra charge! I would have gladly traded the extra oil for 2 quarts of tranny fluid.

 

@C5racecar My oil level is like 1/2 to 3/4 inch over the max line, I drove it back from the dealer after the oil change, any damage done? is it ok to drive over the dealer to get it drained? or doesn't really need to drain and it's no problem?

Really hate going to the dealers. Will this work to suck the oil out is the hose long enough?
www.harborfreight.com/multi-use-transfer-pump-63144.html or

Oil pressure idle was 36 when cold, highway 29 when warm.

If I drain from the dipstick, that's the tank right? and if I drain from the add oil cap, where does that goes exactly?

 

I have never heard of checking the oil with the engine running.

 

For C8 u check the oil level with the engine running. At 170F or higher I believe

 

Ever wonder why you check an automatic transmission with the engine running?? Similar reason. In the case of the C8 oil will drain down from the integrated dry sump tank back to the pan from where it came and you'll get a false low reading!


Yep check with engine off and in time oil in the dry sump tank will flow back to the oil pan where it came from. Probably past the scavenge pump gears. You'll get a false low reading!

 

Yep see pic above. Could drain with a long piece of aquarium air tubing. Take a while but will drain by gravity. Have to suck on the end to get it started. Just have a loop so you can see before it gets in your mouth!

Easier to use a larger hose and drain from the oil fill opening.

 

I have not tried it, but using that pump kit with the adapter for the smaller hose, and running it through dip stick tube might work. I don't think the oil fill opening goes directly to the tank. See picture. Rather, it is connected to the tank via a pipe arrangement with two right angles. It might be difficult to fish a tube around those corners and it might get stuck. The dip stick tube is long but I think that the bends are gradual and the tube might go through easily.

 

Sounds good I will give it a try, the most economic way to do it this way. Got this one for only 5 bucks www.amazon.com/gp/product/B01N8SNNOI/

Anyone know how many quarts I can get the oil out this way? If I can get enough quarts out then I will just do it this way for the oil change next time!! Save the hassle to go to the dealer, pay way too much, and get home to find out that the oil change was done very incorrectly! very frustrated! (What are the chances that dealer will send someone over to get the excess oil out? I mean it's possible to damage the engine if you keep driving it)

 

The engine needs to be off to drain all the oil out of through the drain plug in the oil pan. When the engine runs, it "scavenges" oil from the oil pan and puts it back in the oil tank, where it gets distributed to the engine. So the tank is not filled or full unless the engine is running. Not a good idea to remove all the oil while the engine is running.

 

^^^
Yep, would not have the engine running although to remove 2 quarts may not be an issue except the tubing will get soft.

Suspect the oil will drain down to the pan slowly past the scavenge pump gears. Could check the oil level after say 15 minutes. Could always start a cold engine for a few minute to put the level back.


Suspect when draining oil that 'O" ring at the drain plug tip is sealing a passage from the dry sump tank to the pan and why all oil will drain quickly.

 

Right - to drain excess oil from the tank the engine could (and maybe should) be running so that the oil level in the tank is high. But I was responding to a suggestion that he could actually change the oil just by draining the tank through the dipstick tube. I don't think that would be a good idea.

That is a good point about that second gasket on the drain plug. Perhaps it does help to fully drain the tank when its removed. I never tried to check the tank level before running the engine, so I don't know how quickly it drains down. Also, this discussion makes we wonder how level the in the tank is "regulated". I assume its not. It must pretty much pump most of the oil out of the pan, so the majority of the oil is either in the tank. or in the engine oil lines. It looks like, from the pics attached, that the oil is picked up through a component in the pan called a "crankshaft oil deflector". You can see where it identifies an "oil pump gasket(1)" in the first pic. In the second pic it identifies some screens (3) and some inlet ports (1). Its probably raised slightly from the bottom of the pan so its doesn't quite get all of the oil.

 

Excellent guys, thanks for the help with pictures and explaination etc!! very hepful. (Jerry the aquarium tube you used to get excess oil out, it's the standard size 3/16 inch right. That should work good? I am just going to use the tube with gravity and no pump, might take awhile and few engine starts to get oil into the tank, oh well, definitely won't go back to that dealer again)

 

Interesting that my two C7 dry sumps were the opposite. Took overnight to drain past the scavenge oil pump gears.

Pic is the separate detached dry sump tank.
To check GM said:

• Shut off the engine and check at the tank after 5 minutes (when the oil has drained from the baffles inside the tank.)
• But do not wait more than 10 minutes or some oil will drain back to the pan and you'll get a false low reading.

For fun I checked after it was parked overnight and sure enough oil was below NOT just that Add mark on the hatched area but below the end of the dip stick! At least 6 quarts low.

Some folks could hear the oil being pumped back to the dry sump tank from the pan after parked overnight!


There were two drain plugs in the C7 Dry Sump. One for the oil in the pan and the other for oil draining from the dry sump. Note oil pump is a sliding vain type and computer controlled variable volume (to save energy.) Similar in the C8 (and many modern cars) which is why you see a lower and occasionally step change in oil pressure. The oil scavenge pump is more gear type so oil can flow back when the engine is not running.