This month, while replacing the original alternator on the 318 (5.2L) in my 1992 Dodge B250 van, I discovered the belt tensioner was frozen. A "frozen" belt tensioner usually refers to a bad bearing in the tensioner pulley. The tensioner pulley stops turning and the serpentine belt slips, melts and/or breaks.

This time it was the spring loaded tensioner arm that was frozen. I usually think of tensioner arms becoming too loose and floppy as the spring inside wears out. This tensioner arm was the opposite of floppy. I could not release the tension on the serpentine belt even while levering the tensioner arm with a 24 inch breaker bar. I could feel that the bolt head was going to break off the belt tensioner before the arm ever moved. I cut off the old serpentine belt so that I could remove the alternator.

Once I had the belt tensioner on the workbench, I could see that the tensioner arm spring was rubbing against and corroded into one side of the housing. It was the bearing inside the belt tensioner arm, rather than the bearing inside the belt tensioner pulley that had worn out first.



I was finally able to break the arm free after clamping the belt tensioner in a vise and jerking the arm back and forth with the breaker bar. The arm's tension was uneven and there was a screeching noise as the spring scraped against the housing.

Constant, unrelenting tension only works when there is a separate V-belt for every one or two accessories (alternator, water pump, etc.). Belt tension needs to be continuously adjusted on newer engines (like my 1992!) that have a single serpentine belt following an extremely complicated path to power all the accessories. I do not know for sure if the seized-up belt tensioner arm contributed to my alternator/charging system problems. I do know after installing a new belt tensioner, my A/C compressor no longer makes a rumbling sound when I first switch it on.

Belt tensioners are always inexpensive when compared to the cost of replacing accessories. On most engines it would be a good idea to change the whole belt tensioner assembly (tensioner pulley and tensioner arm) rather than just the tensioner pulley. The cost difference is usually relatively small, and if one tensioner bearing is worn out, then the rest of the tensioner might be close to failing too.



I am not in a hurry to replace more engine accessories, and a new full size passenger van easily costs $50,000 these days, so I treated my Dodge van to a new idler pulley, belt tensioner and serpentine belt. It is a good idea to replace the tensioner and any idler pulleys whenever it is time to replace the serpentine belt. RockAuto's "Belt Drive Component Kits" means buying a complete refresh of a belt system can take just one mouse click.



Tom Taylor,
RockAuto.com