So I replaced the water pump on my girlfriends 2009 Fit and then put a new serpentine belt on. We filled the coolant and test drove for about 45 mins. Normal driving. Got home, popped the hood while engine still running to inspect for leaks or belt wear. Everything looked great. Turned off the engine and the belt snapped.

What could have caused this? All pulleys are turning freely. I know we need to change out the AC Compressor Clutch because it's rattling. Would that have made the belt snap when the car was turned off?

 

Maybe a bad belt? Incorrect tension?

 

did you check the tension is in correct valve? what of the v-belt model did you replace on?

 

How do you adjust tension on the serpentine belt?

 

Brand new belt and happened twice.

 

Assuming that you didn't make an error getting the belt on all the way (it may well be the tightest, most difficult belt I've ever installed regarding physical resistance so that wouldn't be anything to be ashamed of) there would have to be a force exceeding its' strength rating or conditions that lowered its' strength. I'm inclined to assume the latter because of when the belt snapped.

If it's binding on a pulley and, somehow, the belt isn't slipping, I'd think the engine could certainly snap it.
If it's binding on a pulley and it is slipping, along with being subject to a significant amount of tension, it may be getting very hot, and that may weaken it.

While I don't know the temperature tolerance of the average belt, let alone this specific one, I haven't seen a belt located near exhaust components.. Feel free to correct me if there's an example that comes to mind. And they're always in motion when the engine is running, plus they get air from the grill and condenser fan.

If we can suppose that the serpentine belt isn't normally subject to high temperatures, it may be the case that it isn't designed to tolerate them. So if you think your ac compressor clutch isn't disengaging, allowing the pulley to spin freely, that'd definitely be worth inspecting.

You may be able to save some money there if the need is dire. Replacement bearings are reasonable, or maybe the compressor's field coil has the clutch stuck to a seized compressor. If #2 was correct, you could just unplug the compressor's electrical connector. There may also be an ac compressor bypass pulley on the market, where you remove the compressor and replace it with a simple, cheap, regular pulley that takes up slack on the belt. I think others have also hunted down undersized belts that can be used without a compressor or bypass. that'd be in another thread here somewhere.

 

is the belt use in correct parts (38920-RB0-004) ?