How to Replace a 4.3 Blazer Rear Main Seal

by Robert Bayly

The General Motors 4.3 liter V6 engine was introduced in 1985 and is based on the Chevrolet 350 cubic-inch V8 engine. It was used in 1988 through 1995 Chevrolet Blazers. The 4.3 engine uses a one-piece rear main seal mounted in a housing at the rear of the engine block. A bad rear main seal will allow motor oil to leak out between the engine and transmission.

Step 1

Park the Blazer on a level, paved surface and set the parking brake. Raise the front of the vehicle with a jack and support with jack stands.

Step 2

Place a ratchet and socket on the large bolt in the center of the crankshaft pulley. Turn the engine in a clockwise direction until the timing notch in the crankshaft pulley is pointing straight down. The crankshaft must be in this position to remove the oil pan.

Step 3

Remove the transmission from the Blazer. There are several different transmission types for the Blazer. The process will differ, depending on which transmission you have.

Step 4

Place a drain pan under the drain plug on the oil pan. Remove the oil pan drain plug from the pan with a ratchet and socket. Catch the engine oil to drain in the drain pan.

Step 5

Use a ratchet and socket to remove the bolts from the pan. Some engines have studs and nuts. Remove the nuts. Remove the pan from the engine. Note that the oil pan has reinforcement strips along the side. Remove the strips. Clean them and the underside of the oil pan where they fit with a shop rag sprayed with parts cleaner.

Step 6

Use a ratchet and socket to remove the four bolts from the oil seal housing at the rear of the engine block. Remove the housing. Remove the gasket. Spray parts cleaner on a shop rag and clean the gasket surfaces on the engine block and seal housing.

Step 7

Note how far down the seal sits in the housing and which way it faces, so you can install it to the same depth and direction. Insert a flat-head screwdriver into one of the three grooves that are spaced around the housing. Use the screwdriver to pry the seal out of the housing, a little bit at a time, moving from groove to groove. Clean the seal seat with parts cleaner and a shop rag.

Step 8

Set the seal housing on a block of wood. Coat the outside lip of the new seal with clean motor oil. Set the seal in its seat. Place another block of wood on top of the seal. Tap the block with a hammer to drive the seal down into its seat.

Step 9

Mount a new gasket on the engine block. Do not use gasket sealer. Coat the inside lip of the seal with motor oil. Mount the housing on the block. Install and tighten the bolts.

Step 10

Inspect the rubber oil pan gasket for damage, or excessive wear. If the gasket looks good, it can be reused. If it is damaged, remove it, clean the surfaces of the oil pan and engine block with parts cleaner and a shop rag. Mount the gasket on the oil pan. Do not use sealer.

Step 11

Install the oil pan with its reinforcing strips. Install the nuts and bolts by hand. Use a torque wrench to tighten the nuts to 200 inch-pounds. Tighten the bolts to 100 inch-pounds.

Step 12

Reinstall the transmission. Fill the engine with fresh motor oil.

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