ALUMINUM INTAKE MANIFOLD CORROSION (REPAIR PROCEDURE)

VEHICLES AFFECTED: 1985 G,B,E,H MODELS AND 1986 G, B MODELS WITH 5.0L (VIN Y) ENGINE

A mid-year change was made to the intake manifold gasket. All 1985 and early 1986 models with 5.0L (VIN Code Y) engines used a gasket with an insulating sheath applied to the gasket in the area that contacts the intake manifold. This insulating material is dark orange in colour.

LOSS OF COOLANT

There have been cases where the sheath in the area of the coolant passages has deteriorated which resulted in a leak. Most coolant leaks are external; however, there have been cases where coolant leaks have been internal. When investigating a loss of coolant, and a leak is not obvious, remove the intake manifold and examine the gasket for deterioration and evidence of an internal leak in the area of the coolant passages. If an internal leak is found, replacement of heads, blocks or intake manifolds is unnecessary.

REVISED SERVICE GASKETS

The service gaskets will, in the near future, be revised to delete the insulation sheath. When using one of the revised gaskets, it is essential that sealer, part no. 5725836 or equivalent be applied to both sides of the gasket where it contacts the cylinder head and the intake manifold.

Please revise your 1985 Chassis Service Manual and 1986 New Product Service Information Manual - All Series Except Toronado with this information.

Service Procedure:

Intake manifold gasket deterioration as described above may result in corrosion pitting of the aluminum intake manifold.

It is not necessary to replace the intake manifold for this condition. Use a 80% aluminum epoxy such as Devcon "F" or equivalent to fill the corrosion pits in the aluminum intake manifold. Refer to service procedure below.

SERVICE PROCEDURE:

1. Remove intake manifold.

2. Thoroughly clean corroded area using a wire wheel to remove all aluminum oxide.

3. Remove all remaining grit and dust with compressed air, or thoroughly wash in a solvent.

4. Mix epoxy with hardener according to instructions. Apply with a two inch putty knife or similar flat straight edged tool. A heat gun can be used to shorten curing time.

5. After hardening, smooth surface down to its original machined surface using a single cut flat mill file. Observe the voids and fill if necessary. Surface may be smoothed further using 320 grit sandpaper with a sanding block.

6. IMPORTANT: Before reinstalling the intake manifold, it is essential that sealer, part number 5725836 or equivalent be applied to both sides of the intake manifold gasket where it contacts the cylinder head and intake manifold. Refer to illustration.

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.