IsYour Jeep Engine aLeaker?
Fixing the rear main on the 4.0L six
If oil isn’t dripping from beneath your Jeep TJ’s inlinesix, it’s because it’s either
brand new or the rear main seal has been replaced within the last 40,000 miles. That’s just a fact of four-liter life. A leaking rear main seal (RMS) is almost as common among TJs as a leaking valve cover gasket. Both are annoyances that leave the undercarriage a mess, as well as oily spots wherever the Jeep is parked.
Oil seeping from around the back of the valve cover and running down the rear of the engine block can be easily stopped by either re-torquing the valve cover bolts or removing and replacing the old gasket with a new one. A leaking RMS, which typically rears its ugly head with leaking oil originating from between the transmission and the engine, is a little more time consuming.
Fixing the leaking seal entails dropping the exhaust, oil pan, main bearing support bar, and rear main bearing, and then replacing the two-piece seal. It’s one of those jobs that shops we work with typically charge at least a few hundred bucks for. The good news is that doing the RMS repair yourself is relatively easy, and the cost can be less than $50 for the seal and sealants. The six quarts of oil and a new oil filter of course will add to that.
It can be done in a couple hours— providing the exhaust down-pipe bolts come out without breaking off. (Lube them well with penetrating oil the night before.) A basic metric socket set, along with a good torque wrench and a round-nosed punch, are the only tools required. You will need tubes of anaerobic (seals in the absence of air) sealant and RTV sealant, though.
To learn how, follow along as Dunks Performance (in Springfield, Oregon) techs replace the RMS on a customer’s 2006 LJ. The 4.0L had just turned 57,000 miles and it had been seeping oil for six months. The owner of this TJ Unlimited was having a new 4-inch suspension installed, which provided the perfect opportunity to address the oil leak because the front axle assembly and exhaust would already be conveniently out of the way, allowing easy access to the oil pan.