Unfortunately, a leaky rear main seal is pretty common on the 4.0L motor found in most Jeeps. Getting it fixed at the dealership usually runs in the neighborhood of $500, however, if you’ve got a free afternoon, you can fix it yourself for under $50. But be prepared, as my uncle so aptly put it, this is definitely “one of the oiliest jobs possible on a Jeep.” New rear main seals are usually in stock at most auto parts stores, and seem to range from $13 to $15. At that price, you might go ahead and pick up two of them, just in case you mess up one seal during the install like we did… DOH! It might save you from having to make a trip back to the auto parts store, heh-heh…
To start with, depending on how much lift you’ve got, you’ll want to jack up the vehicle by the frame, pull the wheels, and let the front axle hang down to give you clearance to get the oil pan out. Once that’s done, remove the starter and the bazillion bolts holding the oil pan to the bottom of the motor. Oh yeah, don’t forget to drain your oil first!
Now comes the fun part of seperating the pan from the rest of the motor. The XJ we were working on had well over 100,000 miles on it, and had never had the oil pan removed before, so it was a bit stubborn. We had 3 flathead screw drivers and a Stanley “wonder bar” pry bar going around splitting the seal all around the oil pan. It finally popped off after about a half hour of work. To get it out, lower the back half and pull it out under the transmission.
The oil pan was full of black sludge, so it was probably good we pulled it anyway. In addition, the pick-up for the oil filter was nearly clogged with sludge and crystalized gunk. The old oil pan gasket was rock hard, I’d definitely recommend getting a good gasket scraper, or a chisel! Be sure to remove the front and rear neoprene oil seals, they’re pretty easy to pull out and should come off in one piece. Don’t forge to clean the old gasket material off of the bottom of the block as well. We probably spent more time scraping off old gasket than doing anything else…
The rear main seal is located in the back-most bearing cap. It’ll probably take a large breaker bar or impact wrench to get the bolts loose. The bottom half of the seal is in the bearing cap, and if it’s old like the one we were replacing, it may take some work to get all the old seal out. Clean the bearing cap thoroughly to make sure all the old seal is out..
The upper half of the seal is actually inside the block itself. It’s somewhat hard to see too, especially when everything’s covered in oil — the yellow arrows point to the holes where the upper half of the seal goes in. In order to get this upper half out, you’ll need to use a punch or sharp tool (we ended up using a small torx driver and a hammer) to push the seal out from one side. Be very careful not to score the crankshaft. The seal has a metal support wire inside it, this is what you’ll be pushing on with the punch to get the seal out.
Once you get part of the seal coming out the other side, you can grab it with some needle-nose pliers to pull it out the rest of the way. Again, watch that crankshaft…
With the upper half out, carefully insert the new seal half into one of the holes in the block and push it all the way in. An article on the International Full-size Jeep Association website recommended to “coat the block contacting surface at the upper seal with soap, and the lip of the seal with engine oil,” (refer to diagram above). It may help to put a breaker bar on the harmonic balancer on the front of the engine to manually turn the crankshaft. note: the lip of the seal must face to the front of the engine.
Once the upper half is in, coat both sides of the lower seal half’s end tabs with gasket maker, make sure not to get any sealant on the lip of the seal. Next coat the outer surface of the lower seal with soap and the lip of the seal with engine oil, as you did with the upper half. Press the seal into the bearing cap to seat it firmly. Apply gasket maker to both angled edges of the bearing cap, then replace the bearing cap and torque the bolts to the specified torque.
The oil pan is actually pretty clean in these photos, compared to what it looked like when we first pulled it out anyway. Once we got a new gasket scraper, we were able to get the rest of the old material off before putting in the new one-piece oil pan gasket. I’d highly recommend getting the one-piece oil pan gasket, it makes like much easier, and only runs about $32. The part number is #53007568.
Now put the oil pan back into place, put all the bolts back in, put the drain plug back in, and fill the engine with oil, and you’re done!32 comments