I have an odd situation of oil consumption and so far can't find the source.
2003 LS6 C5Z
BTR Stage 2 cam/springs/valve seals replaced in 2019
Stock PCV system with Elite Engineering CC installed per EE instructions for 01-03 LS6 cars)
LS2 TB / Dorman LS2 intake

Below is a screenshot of mileage intervals when I would get a "Low Oil warning". Column on the right are the miles traveled in between these intervals. When this happens oil level is at the bottom dot on dipstick. I would add 1qt to raise level to top dot.

As you can see, it has been getting worse.



Plugs all look similar and not oil covered or a ton of carbon deposit.


I checked spark plugs and none of them look like a motor burning 1qt oil in ~340mi...
I do not see any smoke out the tail pipes at idle/WOT/or deceleration
My CC is not catching a ton of oil either. I have yet to see this car catch even 1/4 can of oil in the catch can.

From my understanding, oil consumption comes from three places. Leaking valve seals, oil leaking past piston rings, or poor PCV system. All of these put oil/contaminates into the combustion chamber...at which point you would assume the spark plugs would be a telling sign of the issue...yet my plugs look "normal"? I don't see any drips of oil on the floor or on the car...

I will continue to drive normally and see if the warning light comes on AGAIN in ~300 mi. From the time I started logging this, nothing has been changed on the motor and is all DD with occasional fun sprints on the highway etc.

Any other suggestions?

 

How is the compression?

 

I have not done a compression test. I did check two cylinders for leakdown.

Cyl 6 was maybe 13% and Cyl3 was perfect.


I realized I needed to rotate motor for each cyl to be TDC but unable to get a socket/wrench on crank bolt with ATI damper and steering rack in the way so I didn’t do all 8 cylinders.

Doesn’t a leakdown and compression test for same thing just using different tools? Can you pass compression but fail leakdown?

 

Definitely a well documented problem for C5 ZO6. Here is one SB up to 2002, I'm sure it carried over for early 2003 builds.

TSB #01-06-01-023A

 

Took these pictures today. I can’t confirm how many miles since I cleaned the tips but I have noticed this is “a thing” that I don’t remember happening years ago





Buddy of mine owns a speed shop and tossed me some new plugs. I’ll replace plugs and top off oil this weekend and drive until warning light comes on again.

Another option is to go ahead and do valve seals again and springs over winter as car sits. Inexpensive to change out.

 

I don't think you have to change the oil anymore.

 

Ha Ha i beat you.

 

I have an oil consumption issue with my '99 LS1. Link to thread

To summarize - It burns some oil between oil changes, but I have not documented it like you have. It'll burn 2 quarts on an HPDE day, no problem, and if I engine decel from a higher RPM I can make thick blue smoke happen at will. I do not have cats to filter out any of the smoke.

Most common causes for oil consumption (once you verify you are not leaking externally)

1. Valve Seals
2. Oil via the PCV system -The internal seal of the LS6 PCV system can fail, replace or repair, and also use catch can to remedy
3. Rings
4. (Only if you have ported heads) You need to use thread sealant on the rocker arm bolts/studs.

Most fixes above can be done in a few hours, except the rings. GM has acknowledged issues for 1999-2001 rings being a problem for oil consumption, and the problem is most apparent with a manual transmission coupled with spirited driving. I guess according to the post above, this was extended to 2002.

Also possible you could have a cracked ring land, or broken piece of ring.

I'm just laying out all the possible scenarios, you still have a fair amount of diagnosing to do.

Compression tests and Leak down tests will show you the health of the top piston ring, but will not give you any insight to the oil control rings sadly.

As for my motor - I have not yet found the smoking gun, but after doing all I can with the top end, it seems to be pointing at the rings. I plan to pull the motor and perform the actions of the TSB outlined above and swap to the updated rings.

 

I do have a "early" 03 with the early style fuel system. At roughly 23k mi in July 2007 I have paperwork showing from a dealership saying the motor was replaced due to the original one being hydro-locked. Car currently has ~85K on it so that puts the motor having ~62K on it. Motor PN at the time was 89017349 on the invoice.

It was done at a Chevrolet dealer in AZ and the PN on the invoice is now "no longer available" on Summit so the motor COULD have been long out of production as of 2007 and an older stock unit was used?? MAYBE a motor that has this known issue?

I'd want to do some digging on motor serial #'s and see what I can dig up in relation to the TSB.

 

If you have all 8 plugs removed, and you still have your accessory belt on, you can easily turn the motor by the alternator pulley bolt.

The Leakdown test will show if air is escaping the cylinder. The air can be getting past the rings, past the valves, or into your coolant (bad head gasket).

Typically the compression test is quicker to do, and if you see a problem here, a leak-down test should follow to help you find where the air is going.

 

Good tip on alternator bolt!

 

Since we're sharing exhaust pics, this is after a wash. I suspect my engine has a ring problem because the right side of the exhaust tips are dirtier than the left. In my mind, indicates a problem with a specific cylinder vs a PCV oil issue.

 

It wouldn't be a bad idea to pick up a compression tester.

Hell it's not a big deal to remove the valley cover to inspect, but again I have a CC that should show signs of PCV issue as it gets the oil, and if that failed then the 02 sensors should show signs if I'm burning oil in the cylinders.

 

So, also my PCV tube from my CC to my intake is NOT full of oil...also explains how I said my intake is NOT excessively covered in oil...also that my CC is NOT having a bunch of oil in it...

IMO that eliminates PCV and leaves valve seals and or rings...

New plugs will go in this weekend along with top off oil and see how far I get until next warning light.

 

If you keep driving that car, don’t wait for your oil light to come on to fill the oil. Keep that oil level full.

 

 

Looks like oil come from the exhaust since your tips are full of it, also if you remove the throttle body you can see if the intake is all oily, if it is your catch can isn’t properly installed

 

CC is installed properly. No oil in the intake...at least not "1qt per 400mi" worth.

Compression tests and leak down will be done by this weekend.

However, I have a funny feeling it's going to come down to a LS6 rebuild or a LS3 drop in.

 

I did a compression test after getting coolant up to 192* and fan kicked on. Let each cylinder pump 5 times:
1 150
3 155
5 155
7 155

2 155
4 155
6 152
8 155

This weekend will be leak down test which I'm having a tricky time being 100% that Cyl 1 is at TDC. Plan is to get 1 to TDC, mark the damper against timing cover (or any fixed object) then mark the damper every 90* from the initial marking. Then I can visually see 90* crank rotation and test the next cylinder in firing order.

My ATI damper and the steering rack in the way is making this more difficult. Normally I would just rotate motor by hand on crank bolt with all spark plugs out...Now I'm thinking to get the car in the air in 4th gear, rotate the wheels to rotate the motor more precisely. However, I'm still needing to find a way to get Cyl 1 at TDC.

 

Spend $20 on Amazon for a cheap endoscope camera that connects to your phone or laptop via USB. You will be able to see each cyl hit TDC.

That little camera is a handy tool to have for many occasions.

Based on your compression tests, I don't suspect you will find any issues doing a leak down test for each cylinder. But I'd be interested in what you find nonetheless. Compression and Leak down tests can't really tell you anything about your oil control rings. Just that the compression ring is in good shape, and that your valves are sealing properly.