Purchased used 05 coup. Had 12,000 km noticed oil consumption. First litre used at 2600km dealer said its normal, top up oil at 1900km oil light on .,,,check oil down below lowest dot on dip stick. Olso noticing carbon on exhaust pipes. The car was sold to me as a signiture series BS with a mod Borla exhaust. Can anyone please tell me if this is normal to be 1 litre low at 1900 km. Car still under warranty and Im frustrated that the dealer has gone to cust serv. tech supports says its normal.
Anyone with knowledgable advice that could advise me it would be very appreciated.

 

don't know litre conversion but you should be less than 1 qt. consumption per 5,000 miles. Make sure you are using the correct oil!
put something down in your garage floor and see if it's leaking.

Most of us are consuming less than 1/2 quart per 3,000 miles driven under conservative driving on c6's.

 

Here is the document for the oil consumption test from GM. It is long, but it touches on everything. It clearly states that 1 quart in 2000 miles is normal, not 1000 miles.

Document ID# 1690890
2005 Chevrolet Corvette


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Subject: Information on Engine Oil Consumption Guidelines #01-06-01-011B - (08/08/2005)



Models: All 1998-2006 Passenger Cars and Gasoline Powered Light Duty Trucks Under 8500 LB GVW (Including Saturn)




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This bulletin is being revised to update the model years, models affected, and oil level check information. Please discard Corporate Bulletin Number 01-06-01-011A (Section 06 -- Engine/Propulsion System).


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All engines require oil to lubricate and protect the load bearing and internal moving parts from wear including cylinder walls, pistons and piston rings. When a piston moves down its cylinder, a thin film of oil is left on the cylinder wall. During the power stroke, part of this oil layer is consumed in the combustion process. As a result, varying rates of oil consumption are accepted as normal in all engines.

Oil Consumption
The accepted rate of oil consumption for engines used in the vehicles referenced is 0.946 liter (1 qt) in 3200 km (2000 mi).

Important: Certain 2006 models have a new GM Extended Warranty. Please refer to the appropriate Owner's Manual for warranty information.

This rate only applies to personal use vehicles, under warranty, that are driven in a non-aggressive manner and maintained in accordance with the appropriate maintenance schedule, with less than 58,000 km (36,000 mi), or 80,450 km (50,000 mi) for Cadillac, driven at legal speeds in an unloaded (for trucks) condition.

Important: This rate does not apply to vehicles that are driven in an aggressive manner, at high RPM, high speeds, or in a loaded condition (for trucks). Oil consumption for vehicles driven under these conditions will be more.

Many factors can affect an owner's concern with oil consumption. Driving habits and vehicle maintenance vary from owner to owner. Thoroughly evaluate each case before deciding whether the vehicle in question has abnormal engine oil consumption.


Gasket and External Leaks
Inspect the oil pan and engine covers for leakage due to over-tightened, damaged, or out of place gaskets. Inspect oil lines and fittings for signs of leakage.


Improper Reading of the Oil Level Indicator (Dipstick)
Verify that the dipstick tube is fully seated in the block. When checking the oil level, make sure the dipstick is wiped clean before taking an oil level reading and fully depress the dipstick until the shoulder bottoms out on the dipstick tube. The dipstick should be the proper part number for the engine/vehicle that is being checked.


Not Waiting Long Enough After Running Engine to Check Oil Level
Some engines require more time than others for the oil to drain back into the crankcase. To assure a sufficient amount of oil has drained back to the crankcase, and an accurate reading can be obtained, the vehicle should be allowed to sit for at least 15 minutes, after the engine has been shut off, before taking an oil level reading. In order to ensure accurate results, the temperature of the oil should be close to the same temperature as the last time the oil level was checked.

Important: This does not apply to 2006 Corvette ZR1 equipped with the 7.0L LS7 engine (dry sump). Follow the instructions in the Owner's Manual for checking the oil in this application.


Improper Oil Fill After an Oil Change
Following an oil change, verify that the proper amount and type of oil was put in the engine and that the oil level on the dipstick is not above the full mark or below the add marks. Refer to the Owner's Manual or Service Manual for information on recommended oil quantity, viscosity, and quality.


Aggressive Driving, High Speed or High RPM Driving
Aggressive driving and/or continuous driving at high speeds/high RPMs will increase oil consumption. Because this may not always be an everyday occurrence, it is hard to determine exactly how much the oil economy will be affected.


Towing or Heavy Usage
Towing a trailer will increase oil consumption and may cause oil consumption to fall below the normal accepted rate referenced in this bulletin for an unloaded vehicle in a personal use application. Large frontal area trailers will further increase the work required from the engine, especially at highway speeds, and thus increases the rate of oil consumption.


Crankcase Ventilation System
Verify that the positive crankcase ventilation (PCV) system is operating properly. Blockages, restrictions, or damage to the PCV system can result in increased oil use.


Oil Dilution (Fuel and Water)
On vehicles that are usually driven short distances, less than 8 km (5 mi), especially in colder weather, unburned fuel and condensation generated from cold engine operation may not get hot enough to evaporate out of the oil. When this occurs, the dipstick may indicate that the oil level is over-full. Subsequent driving on a trip of sufficient length to enable normal engine operating temperature for 30 minutes or more, in order to vaporize excess moisture and fuel, may give the customer the impression of excessive oil consumption.


Engine Temperature
If an engine is run at overheated temperatures (see Owner's Manual or Service Manual) for more than brief periods, oil will oxidize at a faster than normal rate. In addition, gaskets may distort, piston rings may stick, and excessive wear may result. Verify that all cooling system components are in proper working order.


Engine Wear
Piston scuffing, excessive piston-to-wall clearance, tapered or out of round cylinders, worn, damaged or improperly installed valve guides, seals and piston rings will all cause an increase in oil consumption.

Measurement of Oil Consumption
Engines require a period of time to BREAK IN so that moving parts are properly seated. Therefore, oil economy should not be tested until the vehicle has accumulated at least 6400 km (4000 mi). An exception would be allowed only if an engine is reported to be using more than 0.946 liter (1 qt) in 1600 km (1000 mi).

Verify that the engine has no external leaks. Repair as necessary.
Verify that the engine is at normal operating temperature (see Owner's Manual or Service Manual).
Park the vehicle on a level surface.
Wait at least 15 minutes, after the engine is shut off, before checking the oil level to make sure that the oil has had time to drain back into the crankcase.
Verify that the oil level is at, but not above, the full mark on the dipstick, and that the proper viscosity and quality oil are being used as recommended in the Owner's Manual.
Record the vehicle mileage, date, and exact oil level on the form included in this bulletin.
Ask the customer to verify the oil level, each time the vehicle is fueled, following steps 1-6 and return the vehicle to the dealership if the oil level is found at or below the add mark, 0.946 liter (1 qt) low. If the oil level remains above the add mark, the customer should continue to operate the vehicle and verify the engine oil level until 3200 km (2000 mi) has accumulated before returning to the dealership for a final evaluation.
If the final evaluation shows that the engine uses more than 0.946 liter (1 qt) in 3200 km (2000 mi), follow the published symptom diagnostics as described in the appropriate Service Manual. If the oil consumption test shows that the engine uses less than 0.946 liter (1 qt) in 3200 km (2000 mi), explain to the customer that their engine meets the guidelines for oil consumption.
Oil Economy Test -- Data Sheet
Dealer Name: _________________________________

Customer Name: _________________________________

Phone: (___)____-_______ Phone: (___)____-_______

VIN: ____________________________

Oil Type Used: ____________________

R.O. #: ___________________