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Serpentine Belt Failure
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Author:  Bim05 [ Tue Jan 26, 2016 6:06 am ]
Post subject:  Serpentine Belt Failure
Sorry about War and Peace here, but I have never had this happen before.

Was out on a trip yesterday, and on the way back to port (30 min run), I lost power steering to starboard, port side was normal. I didn't hear anything untoward, and my immediate reaction was yet another failed power steering RAM (3 in 4 years!!). There was no other indication that I noticed at the time, and the engine was running fine, so I continued the journey for 20mins more until I came to smoother waters not far from port. It was then I noticed the temp gauge was not registering! I raised the engine hatch as to my horror, I found the belt in the bilge, fortunately in one piece! Managed to get the belt back on OK, and return to port, no further adverse effect apparently.

This was only the 3rd outing from a full service, so the water pump & impeller, belt tensioner, and the belt were all fitted as new parts by the dealer.

Apart from embarrassing myself here as an absolute gumby for not stopping when the steering was abnormal,

What would make a new belt just slip off like that?
More importantly, what damage could have been done to the engine in that 20mins?
Why didn't the engine shut itself down?

VP 5.7L GXi, 320HP

All help appreciated :|
Author:  rpengr [ Tue Jan 26, 2016 8:19 am ]
Post subject:  Re: Serpentine Belt Failure
With the serpentine belt off, you would have lost the power steering, the alternator, the water circulating pump, and maybe the raw water pump (depending on location). There would have been no harm in loosing the power steering and alternator (other than tired arms and dead battery). It is overheat that you are worried about.

If the raw water pump was still being driven by the crankshaft, then hopefully you are OK. Without the circulating pump, you probably had some areas inside the engine that were boiling water, but at least the raw water pump would have tried to keep water in there and also kept cooling the exhaust manifolds. The temperature gage might not have been registering due to low voltage...I'm not sure.

Please answer these questions:

Do you have closed cooling, or raw water cooling?

Where is your raw water pump located? On the front of the crankshaft? or off to the side of the engine?

Was there any "ticking" sounds from the engine when you shut it down? Any other signs of very high heat?
Author:  SpecialK [ Tue Jan 26, 2016 9:26 am ]
Post subject:  Re: Serpentine Belt Failure
Two seasons ago I had the serpentine belt come off of my starboard engine while cruising. Lost power steering quickly followed by increased engine temp. Shut down the engine, raised the engine hatch and found the belt in the bilge. My issue was caused by a loose power steering pump bracket that had just enough play/wiggle to allow the serp belt to come off the pulley. I tightened the bracket attaching bolts and have had no further issues.
Author:  LouC [ Tue Jan 26, 2016 1:46 pm ]
Post subject:  Re: Serpentine Belt Failure
Alignment of pulleys and tensioner a
Failure of the harmonic balancer on the crank pulley. Any of these can cause a belt to jump off. In fact I think it's more common with serp belts than with the older style V belts because of how serp belts wrap around the pulleys.
Author:  Bim05 [ Wed Jan 27, 2016 6:16 am ]
Post subject:  Re: Serpentine Belt Failure
Thanks for your help guys. I rang the dealer today.
He suggested it's a rare occurrence for a new belt to throw off, and I'm dropping the boat off to him in a few days to inspect everything and put the computer over it for any alert codes re: overheating etc.

The water pump is down low on the starboard side.
I believe it's raw water cooling - the dealer suggested that the raw water pump (crank driven?) would keep the engine water circulating well enough for that 20mins.
No ticking sounds at all when I stopped the engine
The temp gauge was not registering a reading when all this was happening - I just didn't associate the steering failure with that fact at the time - obvious now!
I had two brand new fully charged GEL batteries installed as well, so didn't notice a drop in voltage at the time either.

Engine fired up fine for flushing when I got home, seems no ill effects at this point. I'll let you know the outcome next week - might come in handy for someone in the future.

Some lessons learned here for sure,
Thanks again, appreciate it.
Author:  pet575 [ Wed Jan 27, 2016 10:03 am ]
Post subject:  Re: Serpentine Belt Failure
Had a similar thing happen to me a few years back. Turned out that the bearing in the raw water pump failed and caused the pulley to start wobbling. Couldn't see it with naked eye but with engine running you could see it. Caused belt to be thrown and had to replace the entire raw water pump.

In my case, I found out about it because my temp shot up and I got an alarm. I had no idea how long it was thrown because I normally check gauges occasionally while cruising but couldn't remember last time I had checked. Had gone a few miles before getting the alarm.

Seems like you should've/would've gotten the alarm if the temp had gotten too high. That leads me to think that either: (a) you're OK because the circulating pump kept things cool enough until you decided to shut it down; or (b) the temperature sender and gauge need to be checked while your guy is looking things over.

At this point I'd vote for (a) based on your post.
Author:  rpengr [ Wed Jan 27, 2016 10:29 am ]
Post subject:  Re: Serpentine Belt Failure
Bim05 wrote:
The water pump is down low on the starboard side.
I believe it's raw water cooling - the dealer suggested that the raw water pump (crank driven?) would keep the engine water circulating well enough for that 20mins.
No ticking sounds at all when I stopped the engine.

The water pump down low on the starboard side means that it is driven by the serpentine belt also, not crank driven. Unless it has a separate belt...but I have not heard of that.

It is surprising that it could go for 20 min without the raw water pump, but if you didn't have ticking sounds and burnt rubber smell (from exhaust rubber tubes) then you must have not gotten too hot. So probably no harm done.
Author:  Bim05 [ Sun Jan 31, 2016 7:25 pm ]
Post subject:  Re: Serpentine Belt Failure
Dropped it off to the dealer this morning, so I'll post what the findings are next 24hrs or so.
Author:  Bim05 [ Mon Feb 01, 2016 9:35 pm ]
Post subject:  Re: Serpentine Belt Failure
Dealer just called me and advised that i) all the pulleys are perfectly aligned, so that wasn't the issue, ii) no codes indicating any overheating, so that was a relief, and iii) he said the likely cause was a small build up of rust on the pump pulley, and at high revs would cause the belt to become unseated and fly off.

He suggested that even though there was only a short amount of time (8 weeks) since the service, rust can build up quickly. I've had the boat 5 years and this belt is only the third one I've had, all previously replaced as part of a normal service. I'm having difficulty swallowing this as the cause - any comments anyone would like to make on this analysis from your experience? His fix was to remove the pulley, sand blast it clean, repaint it, reinstall it, and of course a new belt!
Author:  rpengr [ Tue Feb 02, 2016 8:59 am ]
Post subject:  Re: Serpentine Belt Failure
Is there any chance that a foreign object fell into the running belt? (a rag, strap, tool, etc)

I'm sure they would have checked the tensioner, but you can verify for yourself that the spring is strong and that it moves without any signs of friction due to corrosion.
Author:  pet575 [ Tue Feb 02, 2016 10:41 am ]
Post subject:  Re: Serpentine Belt Failure
Sounds like most likely answer is that prior technician failed to tighten properly and they are not going to say that out loud.
Author:  rpengr [ Tue Feb 02, 2016 4:03 pm ]
Post subject:  Re: Serpentine Belt Failure
pet575 wrote:
Sounds like most likely answer is that prior technician failed to tighten properly and they are not going to say that out loud.

The "tightening" of a serpentine belt is done with a spring loaded belt tensioner. No adjustment needed by the installer.
Author:  Bim05 [ Tue Feb 02, 2016 9:04 pm ]
Post subject:  Re: Serpentine Belt Failure
Definitely no foreign object fell on the engine area, and last service included a new tensioner as the 'old' one had frozen up, and a new belt.

I just think it's a bit rich to try to cover up something that was overlooked during the service, unless his rust theory has any cred to it - I'm very skeptical!

thanks for your helpful comments guys!
Author:  pet575 [ Wed Feb 03, 2016 10:34 am ]
Post subject:  Re: Serpentine Belt Failure
rpengr wrote:
pet575 wrote:
Sounds like most likely answer is that prior technician failed to tighten properly and they are not going to say that out loud.

The "tightening" of a serpentine belt is done with a spring loaded belt tensioner. No adjustment needed by the installer.


Maybe I'm recalling incorrectly but I am relatively sure that there is a manual tensioner on my 2007 Merc. I'm willing to be proven wrong, just going off of faint memory.
Author:  Bim05 [ Wed Feb 03, 2016 8:01 pm ]
Post subject:  Re: Serpentine Belt Failure
yep, auto-tensioner on my 5.7l GXi, diag link to also show where the small rust built up was causing the belt to fly off (apparently) http://tinyurl.com/zk4q8lk might help someone else in the future.
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