IsYour Jeep En­gine aLeaker?

Fix­ing the rear main on the 4.0L six

Jp Magazine - - TABLE OF CONTENTS - By Bruce W. Smith jped­i­tor@jp­ Pho­tog­ra­phy: Bruce W. Smith

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.

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