Running the Serpentine Belt on a 4.0L Grand Cherokee
The 4.0 liter inline-six in your Grand Cherokee uses a single serpentine belt to drive everything except the timing components. The belt path is straightforward once you can see the layout. Below is the routing for the ZJ and WJ generations, which covers pretty much every Grand Cherokee with that engine. Here is the path. Start at the crankshaft pulley at the bottom center. The belt runs clockwise around the crank, then travels up the front of the engine to the power steering pump pulley on the driver side. From there it drops down to the water pump pulley, crosses over to the alternator pulley on the passenger side, continues to the AC compressor pulley, wraps around the upper idler pulley, and finally comes back down through the tensioner pulley before returning to the crank. The tensioner sits on the bottom left side of the engine (driver side when facing the engine bay). It is a spring-loaded unit with a 15mm bolt head in the center of the arm. You need a 3/8-inch drive ratchet or a long breaker bar on that bolt to compress the tensioner and slip the belt off or back on. The belt itself is a 6PK1185 or equivalent — six ribs, 1185 millimeters in circumference. Melling MB1379 and Gates 6PK1185 are the two I see most often on shelves. The Dorman part is fine too if you are in a bind.
I have replaced more of these than I care to count, and the part that always trips people up is getting the belt routed around the AC compressor pulley. That pulley is tight against the engine block and you need to thread the belt into the groove before applying tension. If you try to seat it after the tensioner is compressed, you will be wrestling with the belt for twenty minutes. Do the compressor first, then the tensioner last. That is the order that actually works. Another thing nobody mentions: the upper idler pulley bearing on these dies a slow death. You will hear a high-pitched whine that gets louder under load, usually from the alternator running harder when the headlights are on. The bearing seizes gradually. When you pull the belt off, spin every pulley by hand. If any of them feel rough or gritty, replace it. The upper idler is about twenty-five dollars and ten minutes of work. Skipping it means your new belt will be making the same noise in six months. Here is the procedure that takes about forty-five minutes with the engine cold. Remove the plastic engine cover first. Pull the driver side wheel well liner enough to see the lower portion of the belt and the tensioner — you do not need to remove the tire, just loosen the three plastic push clips and fold the liner back. Locate the tensioner bolt. Attach your ratchet and rotate the tensioner arm clockwise (toward the engine) to relieve tension. Slip the belt off the tensioner pulley. Note the routing before you remove the belt completely. A quick photo is easier than memorizing it, but the diagram above is accurate for 1993 through 2004 4.0L Grand Cherokees. Install the new belt in reverse order, leaving the tensioner pulley for last. Compress the tensioner again, hook the belt onto the tensioner pulley, and slowly release. Double-check that every rib of the belt sits flush in its pulley groove. Do not force it. Spin the engine by hand two full revolutions with a socket on the crank bolt and re-inspect the routing. Start the engine and listen. If there is any chirping, the belt is not fully seated on one of the pulleys and you need to remove and reinstall it.
A couple of things that can go wrong. The tensioner arm bolt is a soft steel fastener and it strips easily if you use an impact driver on it. Hand tools only. If the bolt is already rounded, the workaround is to use a belt hook tool to hold the tensioner arm while you break the bolt loose with a standard socket. The hook clamps onto the tensioner arm and keeps it compressed so you are not fighting spring pressure the whole time. Also, do not use belt dressing. It is a bandage for a worn tensioner or a glazed belt. If the belt is glazed, replace it. If the tensioner is not holding proper pressure, replace the tensioner assembly. Belt dressing just makes a mess and attracts dirt that accelerates pulley bearing wear. If you need a diagram to reference, search for the Mopar service manual for your specific year. The online PDFs are free through some Chrysler owner forums. The diagram in there matches the routing above but includes the accessory brackets and pulley sizes, which is useful if you are doing more than just a belt replacement.
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The whole job is not hard. It is fiddly because the engine bay is crowded and your hands are small compared to the space between the AC line and the intake manifold. Work slowly, keep the old belt as a routing reference until the new one is fully seated, and check the condition of every pulley before you finish. That is how you make sure you are not back in the driveway in three weeks.
