INTERNAL COOLANT LEAKS (SERVICE PROCEDURES)

SUBJECT: INTERNAL COOLANT LEAKS (SERVICE PROCEDURE)

VEHICLES AFFECTED: 1991-92 "F" CAR

Condition:

--------- Some owners of the above vehicles with a VIN F (LB9 V8) engine built before VIN breakpoint:

Chevrolet NL110563 Pontiac NL205439

or a VIN 8 (L98 V8) engine built before VIN breakpoint:

Chevrolet NL111173 Pontiac NL205712

may comment on a loss of engine coolant without visible coolant leaks.

Cause:

----- This condition may be caused by an internal coolant leak between the cylinder head and intake manifold at the coolant crossover passages. One cause may be a cylinder head casting dimensional problem, to determine if cylinder head is the cause.

Perform the following procedure:

1. Remove the rocker covers.

2. Remove the intake manifold.

3. Measure the distance between the rocker cover mounting flange and the bottom of the coolant passages (front and rear) (see Figure).

4. If the distance is less than 66 mm (2.60 inches), replace the cylinder head(s) with the following part numbers.

LB9 V8 Engine, P/N 10159553

L98 V8 Engine, P/N 10159552

Parts are currently available from CANSPO.

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.