ENGINE OIL ECONOMY (INFORMATIONAL BULLETIN)

SUBJECT: ENGINE OIL ECONOMY (INFORMATIONAL BULLETIN)

VEHICLES AFFECTED: 1982-93 "C,D,E,K,V" MODELS AND LIGHT TRUCKS

THIS BULLETIN SUPERSEDES AND REPLACES CORPORATE BULLETIN REFERENCE NUMBER 716105R.** THIS BULLETIN IS BEING REVISED TO ADD METRIC MEASUREMENTS.

This bulletin will serve as a guideline for engine oil economy. Included is information concerning:

I. HOW TO ESTABLISH AN ACCURATE MEASURE OF OIL ECONOMY. --------------------------------------------------- o What should be considered acceptable oil economy.

o Factors which can reduce oil economy.

Test Procedure

The procedure listed below should be used to determine engine oil economy:

1. The engine must have at least 5,000 KM (3,000 miles) before it is possible to get an accurate indication of oil economy due to the effects of engine break in. An engine with oil economy of 800 KM per Liter (500 miles per quart) or less should be checked immediately to determine the cause.

2. All sources of external oil leaks should be checked and corrected as necessary before this test is run.

3. The engine oil dipstick and tube should be checked to verify they conform to design specifications. Refer to Item III.

4. Add oil until the level reads near the top of the full range on the dipstick. Refer to step 5 below.

5. A 20 minute drain back time is required before an accurate dipstick reading can be obtained.

6. Determine that the proper viscosity oil is being used. Thin oils have poorer oil economy than thicker oils.

7. Read the dipstick and record the oil level in the Customers File

8. Return the car to the owner. Instruct the owner to:

a. Check the oil level weekly after 25 KM (15 miles) of highway-type driving and after allowing the oil to drain back for 20 minutes.

b. Add oil only when the dipstick level reads add One Liter (one quart) below and only in One Liter (one quart) increments.

c. Record the mileage and amount of oil added in the Customers File.

9. After the owner has driven the car for 2,000 miles, the car and data sheet should be returned for evaluation.

II. GUIDELINES ---------- The following should be used when evaluating engine oil economy:

1. 1,000 miles or more per quart economy indicates acceptable oil economy.

2. Fewer than 1,000 miles per quart indicates action should be taken. Item III below will present a logical approach to diagnosis. A new engine that starts in this area will generally improve during break in.

III. DIAGNOSIS --------- The many factors which can cause poor oil economy can be separated into two basic areas: engine mechanical conditions and engine related conditions.

Engine Related Conditions:

1. Miscalibration of the oil dipstick can make it appear that there is a poor oil economy condition. Overfilling of the crankcase can result in poor oil economy due to foaming of the oil and excessive oil splash.

2. A careful inspection should be made of the PCV system. An unseated PCV check valve can cause poor economy due to excessive blow by. A kinked or collapsed PCV hose can cause poor oil economy due to increased pressure blowing oil into the air cleaner. A restricted PCV system can also cause rapid oil deterioration. Changing the valve and/or hose is usually the correction. Oil accumulation in the air cleaner and/or excessive wetting of the element is a clue that the PCV system should be carefully inspected.

Engine Mechanical Conditions:

3. A loose intake manifold may allow oil to be drawn into either the intake ports or exhaust heat crossover passages resulting in poor oil economy.

4. Piston Rings

a. Missing or broken piston rings.

b. Compression rings installed upside down.

c. Compression ring gaps aligned; particularly on several cylinders. NOTE: During engine assembly the oil ring rail gaps normally can be aligned. This will not contribute to poor oil economy.

d. Scuffed rings and/or scored cylinder bores.

e. Rings stuck in the grooves or excessive ring side clearance.

f. Oil ring expander overlapped and not exerting pressure on the rails.

5. Valves

a. Missing or broken valve stem seals; particularly on the intake valves.

b. Excessive valve guide wear.

6. Mismachined cylinder walls. This would be seen as a low spot where rings fail to contact the cylinder wall or as many small holes in the cylinder wall surface or a cylinder that was only partially honed.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.