4.0L exhaust manifold weak on Comanche

by (anonymous)

Overall the Comanche has been a great truck. I have owned it six years now and only one major problem. The exhaust manifold. The I-6 4.0L engine is very strong and reliable, however Jeep has a design flaw they neglect to fix on the exhaust manifold. Since the engine is a straight six cylinder (i.e. inline-6) there is one manifold connected to the engine block. At the point where each of the exhaust ports branch together, after about 75,000 miles on the vehicle the manifold cracks. This happens on most I-6 engines. When you replace it, do not buy a factory manifold, purchase a Borla Stainless Steel header. The cost is about Overall the Comanche has been a great truck. I have owned if six years now and only one major problem. The exhaust manifold. The I-6 4.0L engine is very strong and reliable, however Jeep has a design flaw they neglect to fix on the exhaust manifold. Since the engine is a straight six cylinder (i.e. inline-6) there is one manifold connected to the engine block. At the point where each of the exhaust ports branch together, after about 75,000 miles on the vehicle the manifold cracks. This happens on most I-6 engines. When you replace it, do not buy a factory manifold, purchase a Borla Stainless Steel header. The cost is about $330 for the part and about $300 to install it. This exhaust header comes with million mile warranty, now you will be protected for life. The reason the factory exhaust manifold cracks is because the exhaust system is rigidly mounted to the under body of the vehicle. As the engine increases power it rotates clockwise from the centrifugal force of the cam shaft. When this occurs internal stresses are placed on the exhaust system and where the exhaust manifold branches together creates a stress concentration area and eventually over time it cracks. (i.e. if you take a playing card from a deck of cards and put a circular hole in it, then bend the card back and forth eventually it will tear at the hole location first) Even though this engine has this design flaw don't let it scare you away from purchasing a Jeep product with this engine.I have 127,000 miles on my Comanche and still have the original clutch. The mileage is not so good.It doesn't include a 4 wheel drive.