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4.0L Oil Pan, Rear Main Bearing Seal Install Jeep TJ/Rubicon


Gather all parts

Drain fluids

Remove skids

Spun the nutsert, drill hole in frame 

Tack weld inside

Remove starter

Pull pan and bearing brace

Bearing brace

Remove rear main cap & remove/install upper rear main seal

Remove rear main seal

Carefully remove rear main seal and install new one

Too much wheeling and too many hard hits on my old TbT oil pan skid had finally taken it toll. The bottom of the oil pan was beaten more in than out and a new stronger skid was in order.

The engine check light had been telling me I had a bad number 1 cat, the one closest to the firewall on ’03 TJs, which has 3 cats. Two sat just under the exhaust manifold and one was back by the transfer case. Since they are welded in and part of the Y-pipe assembly from DC Jeep, it was best to replace the entire Y-pipe.

The rear main seal had been leaking almost since day one and albeit was not much more than a wet spot on my oil pan, I figured that since I was in there I might as well replace it also.

I strongly recommend using OEM parts for  gaskets, seals and oil pan because they fit!


  Mostly common hand tools except you will need a long extension with a universal joint on the end for the remove/install of the bolts that hold on the Y-pipe at the header.

  • Torque wrench
  • Sockets - 11mm, 12mm, 13mm, 14mm, 15mm 16mm
  • 3/8 and ½ drive Ratchets
  • Needle nose pliers
  • Small drift punch or screwdriver


Expect to spend a good 4 hours if there are no issues.

 Approx. costs:

  • Y-pipe, $325 - $450
  • OEM Oil pan, $90
  • Nth Oil pan skid [std trans], $160
  • OEM gaskets and rear main seal, $45
  • 6 quarts Mobil 1 oil and oil filter, $35

 Rear Oil Seal Install:

  • Wipe the seal surface area of the crankshaft until it is clean.
  • Apply a thin coat of engine oil.
  • Coat lip of the seal with engine oil.
  • Carefully position the upper seal into the groove in the cylinder block. The lip of the seal faces toward the front of the engine.
  • Apply Gasket Maker sealer on both sides of cylinder block as shown in. The dab of sealer should be 3 mm (0.125 in.) in diameter.
  • Apply Mopart Gasket Maker on the rear bearing cap. The bead should be 2.3 mm (0.09 in.) in diameter. DO NOT apply sealer to the lip of the seal.
  • Position the lower seal into the bearing cap recess and seat it firmly. Be sure the seal is flush with the cylinder block pan rail.
  • Coat the outer curved surface of the lower seal with soap and the lip of the seal with engine oil.
  • Install the rear main bearing cap. DO NOT strike the cap more than twice for proper engagement.
  • Tighten all main bearing bolts to 80 ft lbs of torque.
  • Install the main bearing cap brace. Tighten nuts to 35 f. lbs.
  • Install the oil pan gasket and add oil
TIP on Rear Main Seal Install (thanks to the fine folks at 4 Wheel Supply :

  The primary reason for new rear main seals leaking is (after installation) the torn backside of the seal. Because there is a pre-load on the (upper half) seal when installed, it is all too easy to cut/tear the rubber off the back side of the seal where it meets the sharp machined edge of the back of the block (thereby creating gap and/or unequal pressure along surface).


  A thin piece of plastic (ie. the stuff used to package card would work, but is a little thick). Cut the plastic so that it has an ear the width of the seal journal and about 1/4 inch long. Insert the ear into backside of the journal (you are using it as you would a shoe horn to cover the sharp edge) Cover back side of seal with LIGHT coat of RTV (acts as lubricant during installation and seal when done). Seal will slide in like a greased pig on hard ice (as opposed to having to tap in with hammer). SMALL dab of RTV on mating surface (ends) of seal... DO NOT put RTV on mating surface of bearing cap; this will destroy proper bearing clearance.

 Oil Pan Install:

  • Clean the block and pan gasket surfaces.
  • Apply Silicone Rubber Adhesive Sealant on cylinder block to rear main bearing cap corners and cylinder block to front cover joints (four places).
  • Slide the one-piece gasket onto the block and timing case cover.
  • Position the oil pan on the gasket.
  • Install the 1/4 inch oil pan bolts. Tighten bolts to 84 in. lbs torque. Install the 5/16 inch oil pan bolts. Tighten these bolts to 132 in. lbs torque.
  • Install starter motor.
  • Connect the exhaust pipe to the hanger and to the engine exhaust manifold.
  • Install transmission oil cooling lines (if equipped) and oxygen sensor wiring supports that attach to the oil pan studs.
  • Install the oil pan drain plug. Tighten the plug to 34 25 ft. lbs. torque.

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