TIMING CHAIN RATTLE NOISE FROM ENGINE ON START UP

SUBJECT: TIMING CHAIN RATTLE TYPE NOISE FROM ENGINE ON STARTUP (INSTALL PF1225 ENGINE OIL FILTER)

VEHICLES AFFECTED: 1987-90 N, W, L, L4 W/2.3L

Some owners of 1987-90 N-W-L models equipped with a 2.3L models equipped with a 2.3L may comment about a rattle type noise from the engine when the vehicle is first started. This noise will then usually disappear within a few seconds.

This condition may be the result of oil in the engine oil filter draining back into the crankcase after the engine has been shut off. As a result, engine oil pressure sufficient to fully extend the timing chain tensioner plunger to properly tension the timing chain may be delayed a few seconds when the engine is started. While there is no adverse effect on component durability or performance, timing chain noise may occur for this brief period of time.

To minimize oil filter drain back and timing chain startup rattle noise, it is recommended that an AC Rochester, PF1225 (GM P/N 25014233) oil filter be installed. This filter exhibits excellent anti-drain back characteristics and is now being used in Production. The PF1225 is also the recommended service replacement oil filter for this engine.

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.