Help Diagnose "Jumpy" Belt Tensioner (VIDEO)

[sfbayjay]

Hi all,

Been struggling to pin down an issue under the hood of my 2002 XLT 4.0L V6.

Last week the large coolant hose that runs from the bottom of the coolant reservoir to the bottom of the radiator was CUT and started spewing coolant everywhere! Fun!

I found out that the belt tensioner, right next to the cut hose, is "jumping" when the truck was at idle, just enough to make contact with the hose and make a nice clean slice. This ONLY happens at idle - once engine speed is increased everything runs smoothly and the "jump" vanishes.

I have since replaced the hose, and also changed the belt (new Gatorback), the belt tensioner, and the idler pulley. Neither the tensioner or idler seemed in bad shape, but they were cheap and easy to swap so I crossed my fingers but, no dice - still jumping.

I've done a ton of reading about this here on the forum, but I can't seem to narrow down the problem. Too many possibilities: water pump, clutch fan, power steering pump/pulley, AC, harmonic balancer.

I don't have ANY chirp/squeak or noises with this problem, just the tensioner "jump" at idle - goes away and smooth as silk once RPMs are increased at all.

Here's a video I put together. Have a look and let me know if you have any thoughts on how to narrow down this problem! I really don't want to start throwing money at parts that don't need to be replaced if I can help it.

Link to Video: https://www.youtube.com/watch?v=g_H8hNqc

 

[sfbayjay]

Really? No replies to my incredible and awesome serpentine belt video? (I've been hearing some Oscar buzz)

Seriously - anyone?

Forgot to mention in my prior post or in video - no apparent issues with alternator. Pulley seems smooth and yesterday's load test suggests it's working well.

A trusted friend has suggested I consider replacing the power steering pump, largely due to play in the pulley (near end of video). He thinks that maybe the pulley is binding when loaded by the belt tension, even though it spins freely when the belt is off.

Thoughts?

 

[2000StreetRod]

steady idle?

I watched your video (which was very well done) twice and the only thing suspicious I noticed was the slop in the power steering pump but I doubted that was causing the tensioner to jump. How steady is the engine rpm at idle? Do you have any misfire DTCs?

 

[sfbayjay]

Engine idle speed is dead steady, no surging or strangeness. Honestly, the truck runs GREAT other than the tensioner jumpiness.

Had codes checked a few weeks back when CEL came on - only code was P0125 - low coolant temp. Thermostat was stuck open or ECT sensor was bad - changed thermostat and sensor, cleared CEL light, and no more problems since. No more CEL light since, either. Truck was running cooler than usual, consistent with stuck thermostat. After changing therm, back to normal temp on gage and rock solid.

Trying to decide now whether play in the PS pulley is enough reason to change it out and see what happens. May not fix the original jumping tensioner issue. Could end up chasing this thing all the way around the serp belt. Ugh.

Maybe I'll have codes checked again to be sure nothing new has showed up, but there's no CEL.

As always - any ideas welcome!

 

[sfbayjay]

Thinking about this some more - here's more back-story, although possibly not related.

The day this problem first surfaced, as mentioned in my first post, the coolant hose between the bottom of the coolant reservoir and the bottom of the radiator was sliced open when the jumpy tensioner hit the hose when the engine was idling. Thinking back on that, here's how it went down (in the parking lot of the veterinarian with a yowling cat in the back seat - bonus):

1. Started truck, idling for awhile w/ AC running while on the phone, maybe 3 minutes.

2. Backed out of parking space, made 2 or 3 tight turns to maneuver to front door of vet clinic.

3. Idled there about 3 mins waiting w/ AC running.

4. When I attempted to pull away, had no power steering. Crap! No noises or other symptoms - engine running smoothly and AC blasting cold air.

5. Backed up a bit to re-park and figure things out. Noticed coolant everywhere on ground where I’d been sitting.

6. Truck in park. Pop hood. Hot coolant flying everywhere! The slice in the belt was squirting coolant right onto the serp belt where it came around the tensioner and the belt was throwing the coolant EVERYWHERE!

7. Slammed the hood, turned off the AC, and power steering immediately came back to life.

8. Quickly drove home with steaming truck. Replaced the coolant hose, replaced belt tensioner, belt, and idler pulley.

That about brings things up to the present.

At the time, I figured that the temporary loss of power steering in the parking lot was because the belt had been soaked with coolant and was slipping over the PS pulley. Now I think maybe the PS pump and/or pulley bound up for a minute when I was making tight turns, the tensioner jumped around and sliced the hose, then somehow turning off the AC compressor gave just enough of a tweak to free up the PS pump/pulley.

Thoughts?

 

[budweiser]

Mybe the belt is alittle to long and its not tensioned enough and its jumping around I bought a belt for my 03 explorer and it was longer than the one I took off and noticed it would have rubbed my rad hose my want to check the belt mybe wrong on like mine was.

 

[sfbayjay]

Update: Jumpy belt tensioner

Well - it wasn't the power steering pump. :thumbdwn:

Changed out the pump this weekend and the problem remains.

I can also rule out the fan clutch, as I checked things out with the fan disconnected.

That leaves alternator, water pump, AC, or harmonic balancer.

I checked all 4 of these remaining components very carefully when I had things apart to change the PS pump. I can't really find anything obvious. No play in any of the remaining pulleys and no noise from any of them when spun.

I'm stumped. :scratch:

 

[zpn_by]

remove the belt and try to spin each accessory pulley by hand. Any indications of snags or catching? could be that the belt is driving fine, until it gets to a snag on one of the accessories, then skips. Also, after coolant spraying everywhere, while the belt is off clean each pulley with soapy water and a scrub brush, in case there is coolant left in the grooves/on the smooth parts. Seems simple, but you never know, and at least these are no-cost checks. Good luck!

 

[budweiser]

guys the fan belt is to long your wasting money buying all that stuff. if the belt is to long the tensior aint got enough tenson on the spring like it should which results in it jumping around. take that belt back to where you got it get the right belt I just had to do this on my 2003 explorer.

 

[sfbayjay]

guys the fan belt is to long your wasting money buying all that stuff. if the belt is to long the tensior aint got enough tenson on the spring like it should which results in it jumping around. take that belt back to where you got it get the right belt I just had to do this on my 2003 explorer.

Thanks for the suggestion, but I am definitely running the right belt. A brand new Goodyear Gatorback - same size/brand/type I've used for the last 100K miles with no problems.

 

[sfbayjay]

remove the belt and try to spin each accessory pulley by hand. Any indications of snags or catching? could be that the belt is driving fine, until it gets to a snag on one of the accessories, then skips. Also, after coolant spraying everywhere, while the belt is off clean each pulley with soapy water and a scrub brush, in case there is coolant left in the grooves/on the smooth parts. Seems simple, but you never know, and at least these are no-cost checks. Good luck!

Thanks for the ideas - I did clean up everything really well after the original coolant disaster. Cleaned up all the pulleys and changed the old belt. In fact, I bet the old belt had plenty of life left after only 45K miles, but I changed it anyway.

I haven't found any damage or rough spots on the pulleys. The old belt was worn very evenly with no signs of damage.

 

[zpn_by]

I haven't found any damage or rough spots on the pulleys. The old belt was worn very evenly with no signs of damage.

I'm glad to hear everything was done properly - some people forget that coolant can make a belt slip. However, I meant to spin each pulley by hand to check its motion, not it's surface. Let's say your power steering pump has a catch in its impeller as it spins within the pump - you can't see anything from outside, but you could certainly feel it if you move the pump a few rotations by hand. Try this for each of the accessories - water pump, alternator, steering pump, AC. You may find the cause there...