Overheat Due to Shredded Serpentine Belt

[Philip Swofford]

All,
I had an overheat event the other day. I have a 2001 32′ Topaz express with twin Cummins 370B’s and usually run at 20 knots cruise around 2400 rpms. At WOT, I can get 3100 rpms no problem. Anyway, I was running about 2400 rpm and shredded a serpentine belt on my port engine. The Aqualarm alarm panel and Seaboard sensors I installed worked as expected (I have the SMX 205F temp switch installed at the point on the exhaust manifold where you could mount the turbo in an alternate configuration). I throttled back to idle and shut the port engine down within 5-10 seconds of the alarm. There was coolant and shredded belt material all over the front of the engine. I ran in the couple of miles on the starboard engine. I let the engines cool down overnight and the next day cleaned everything up. I installed a new belt and added a couple gallons of coolant. I cranked the engine up and monitored the coolant level and topped it up just a little as the air worked out of the system. It seemed to crank and run fine and I couldn’t see any leaks or cracks in the exhaust manifold or coolant in the oil. I didn’t have a chance to run it up to cruise as the weather was awful. I hope I’ve dodged a bullet, but only time will tell.

Now, I’d like some advice. This engine has shredded a belt before, but I caught it before it broke. After it broke the first time, I inspected all the pulleys and made sure everything was turning easily and smoothly. I couldn’t see anything the looked massively out of order at the time. Since then, I keep an eye on it, but I haven’t noticed it shedding any excess material. I can’t see that anything is misaligned, but I’m still investigating that. I bought the belts I have from Seaboard, so I know they’re correct. I’m relocating my coolant overflow tanks, so I can do away with the belt guards and better see what’s going on with the belts.

Any advice on what I should look at? Pulleys out of plane/misaligned? Need a shorter belt? What do you typically see a lot?

The next question is, should I change to the 190F temp switch and the 160F thermostat so that if this happens again, I’ve got a little more cushion before major damage could occur?

I appreciate any help.

Thanks!

Philip Swofford

Topic

[Philip Swofford]

Thanks for the reply Donald!

The boat is in Orange Beach, AL and it was used over the winter, so it wasn’t laid up for months like a lot of northern boats.

I plan on doing exactly as you suggested with a straight edge to check on the pulley alignment. I am re-locating the coolant overflow tanks so I can get rid of the belt guards and make checking this stuff out a lot easier.

I checked all of the pulleys and they all spin smooth with no slack back and forth. The water pump and tensioner pulley surfaces are totally smooth, but the alternator, and idler pulleys and harmonic balancer are a bit rough. I’ve run other boats with pulleys in similar condition and never had any issues, but this may be an issue with this one. I plan on replacing or cleaning them up.

As far as a high output alternator, I’m not sure. I bought this boat used and its had a few owners. I meant to get the part number off of the alternator to make sure about what I have, but I forgot to when I left it Monday.

The boat apparently had some less than diligent owners over its life. The guy I bought the boat from had done a lot to bring the maintenance up to par, and I’m continuing that trend. I have to keep telling myself this is a marathon, not a sprint!

[donald roth]

The problem could originate from the alternator, circulation pump, or idler pulley, or as you mentioned above, misalignment of the pulleys.
Without the belt, turn each pulley, feeling for resistance or grinding, then try to move them radially, feeling for play in brackets, bearings, and mount points.
Lay a straightedge across the face of the damper and measure to each pulley, should be very close on all.
Do you have a HO alternator? These can put a lot of strain on the belt.
Are all the pulleys clean and free of rust in the shivs?
I give the belts an occasional squirt of Armor All, keeps them supple and quiet.
Don’t know where you’re located, but if you are coming out of winter layup, and did not slack the belt over the winter, that might have added to its demise.

[Author]

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