For 1990-2009 cars

# INTERNAL COOLANT LEAKS (SERVICE PROCEDURES)

#### Subject: INTERNAL COOLANT LEAKS (SERVICE PROCEDURE)

#### Models Affected: 1991-92 FIREBIRD MODELS -----------------------------------------------------------------------------

#### Condition:

---------- Some owners of the above vehicles with a VIN F (LB9 V8) engine built before VIN breakpoint NL205439.

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

#### Correction:

----------- 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 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 GMSPO.

Labor Operation: T1800

Labor Time: Inspect both cylinder heads 10.3 with A.C. +.1

Clean part on vehicles with 30,000 plus miles +.3

Replace head (right or left) .6 Replace both heads 1.1

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.