Serpentine belt slips off idler pulley

My guess would be you either have an oil leak that is causing the smell and causing the serpentine belt to slip, or you have a pulley for the serpentine belt that is not spinning freely and causing the belt to slip. A slipping belt can also cause the burning smell that you describe. You might have a AC compressor clutch that is failing and not freewheeling correctly, you could have an alternator with a bad bearing, you could have an idler pulley or tensioner pulley with a bad bearing, etc. I'd certainly be checking for an oil leak as well though.

IT COULD BE AN IDLER, TENSIONER, OR THE BELT SLIPPING, THESE ARE SEALED YOU CAN'T LUBE THEM. IT SOUNDS LIKE THE BELT IS SLIPPING, BUT IT COULD BE SLIPPING BECAUSE OF A FAULTY IDLER\TENSIONER. REMOVE THE BELT, MAKE SURE ENGINE IS SHUT OFF, AND YOU HAVE THE KEYS, ROTATE ALL THE PULLEY'S AND THE ALTERNATOR PULLEY THEY SHOULD ROTATE FREELY AND RUN TRUE, AND NO ROUGH FEEL TO THEM, OR THE TENSION COULD BE TOO WEEK TO KEEP THE BELT TIGHT.

This can be caused and often is by a defective crankshaft harmonic damper pulley.

for a 5.7 liter, start a the crank pulley,go clockwise around the waterpump pulley,go downto the power steering pulley,up to the a/c comppressor,under the idler pulley,up to the alternator pulley,and the slip the belt onto the tensioner pulley.

This pulley should be spring loaded and you should have a diagram of the belt path on a label under the hood. There should be a square hole in the casting for a breaker bar or rachet to use as a lever to push or pull the pulley.

One of the secrets to installing the belt is not using the Idler pulley as the last pulley the belt attaches to. You are better off to use a stationary pulley in an easy to reach area as the last pulley to slip the belt over. In some cases you can just lean on the Idler pulley and press it down with the belt already over it. Then use the slack to slip the belt over another pulley, stationary, like the Alternator or water pump pulley.

If in doubt about out or in for the spring, just look at the diagram and see which side of the picture shows the belt looping around it. It (Idler pulley) is always suppose to push against the belt. If the belt runs to the right of the Idler, the spring pushes right. up to up, down to down, left to left. This means you get clearance by pushing the Idler in the opposite direction.

I hope this helps. Thanks for using Fixya.

There should be a diagram attached to the car near where the belt goes showing how the belt is to run through the pulleys.
Newer vehicles have a tension pulley which is a pulley on a spring loaded arm that keeps the belt tight.

First run the belt on all the other pulleys and then use a wrench to hold the tension pulley back while you slip the belt on.

Older cars do not have a tension pulley and you had to usually loosen something like the alternator a little bit to get it on.

On this particular model of the 1998 Dodge Grand Caravan I determined that the upper hose from the water pump had slipped off and anti-freeze squirted on the serpentine belt causing it to slip off. Once the belt gets slick it never stays on. I replaced the belt by loosing the tensioner which is the idler pulley located in the center of the configuration, A big thanks to user motor1258for the configuration diagram.

Don't have a chart, video, or diagram available at the moment. Can offer you generic advice.

1.Somewhere in the middle of that serpentine belt, that is wrapped around all those pulleys, is an Idler tensioner Pulley. All this pulley does, is put tension on that serpentine belt. Usually located somewhere in the middle.

The Idler tensioner Pulley will be on a bracket. It will be on the end of the bracket. The bracket usually has a 1/2 inch square hole in it. This is used for a tool, that resembles a 1/2 inch breaker bar.
-> I, use a 1/2 inch breaker bar.
The 1/2 inch breaker bar is inserted into this square hole, and the bracket is pulled to one side.
This pulls the tensioner pulley away from the serpentine belt, allowing the belt to have slack, and then the belt is slipped off of one of those pulleys. Release the pressure slowly, remove the tool. Then the serpentine belt is removed all the way.

(The Idler tensioner pulley bracket, can only be moved in one direction, to take pressure off of the serpentine belt. The direction opposite, of it putting pressure on the serpentine belt.

The spring used to put pressure is Very strong. This is also an area, where you can easily slip, cutting your knuckles, or fingers, or hand, on sharp objects. Use caution, you may want to wear a glove, or gloves!)

Then the new serpentine belt is wound around the pulleys in the correct pattern, the Idler Tensioner Pulley is once again pulled to the side, and the last of the serpentine belt is slid into place. Then you slowly release the tensioner pulley, and it puts pressure on the serpentine belt once more.

Make sure the serpentine belt is in the grooves of the pulleys, and is wound around in the correct pattern.

On the car hood inside, or on the radiator support, or perhaps on the inner fender well, or in the Owners Manual, it should show the correct pattern for installing the serpentine belt.

Your '90 Benz has a belt tensioner that is automatic. You just insert the correct tool to ease the tensioner pulley, (The tool is inserted into the bracket for the tensioner pulley), to the left as you're facing the car. Then slip your serpentine belt off. Reinstallation is a reversal of this process. (I believe it's to the left, don't quote me on that)

The radiator support in front, should have a diagram of how the serpentine belt goes on the pulleys.

If your serpentine belt slips, then the belt tensioner pulley assembly is bad, needs to be replaced, or the serpentine belt itself is worn out.

Try using a 1/2 inch socket on your heaviest socket wrench. Put it on the nut on the idler pulley and push the idler back to allow you to slip on the belt.