Cat 3208 Raw Water Intermittent Stop

Two days ago I heard the distinct change in engine exhaust that normally tells me the raw water pump belt has failed. Engine temp climbed, I throttled back and prepared to grab a mooring to check it out. Then engine temp went back down and engine sound returned to normal. No other problems during a couple more trips that day. Yesterday same thing. Engine temp spiked up, but after some time on the morning all was back and doing OK.

Today I'm troubleshooting. Strainer is clean. Pulled raw water pump and impeller is in good shape. I'm rapidly running out of ideas (actually I'm already out of ideas) on what can be causing this to happen intermittently.

Cat 3208 375hp turbo.

Any advise is appreciated.

I have same motors, perhaps something is choking off the intake such as a piece of plastic bag which is flopping around & randomly restricting flow? Falls away when you idle back?

Impeller keyway wore allowing impeller to spin on shaft under load?

Just some thoughts.

Thank you for the reply. The intake is clear. My first thought was that something had been pinned against the intake but it's completely clear. (We're a dive shop so going underwater to check it wasn't a problem). The impeller is in great shape. I was really hoping it was the impeller as that would be an easy fix. Now I'm putting everything back together but still don't know what caused it. Thanks again for trying to help.

Belt slip?? Pulley slip on shaft (rare, if not downright impossible).

Raw water hoses can delaminate from the inside. They'll get hot and the block the water flow. Then cool down and seem to work again. Do if any of your hoses are older check them out from the inside.

Ski in NC said:

Belt slip?? Pulley slip on shaft (rare, if not downright impossible).

Click to expand...

The belt was definitely loose but that would seem to make a continuous overheat problem not the intermittent one I'm getting. I could be wrong. I'm putting the water pump back together now and will be putting it back in with a properly tightened belt.

Check your hoses!

Capt.Bill11 said:

Raw water hoses can delaminate from the inside. They'll get hot and the block the water flow. Then cool down and seem to work again. Do if any of your hoses are older check them out from the inside.

Click to expand...

They can separate internally and under suction close off under higher flow and seem to repair themselves at lower volumes. Start with the sea strainer to pump. Check the bearings on your pump, they may be heating up and causing the belt to slip. I think that pump shares the same impeller as the standard Sherwood pump that comes on the 330B Cummins. If that's the case there are three cassette bearings between the impeller and the pulley. The Cummins is gear driven but I think the pump is similar. I've had bearing failure on the Cummins.

Did this problem occur right after a start? Pump takes a lot of torque to get it spinning, then once spinning it is pretty easy.

Anyhow, my vote is for loose belt.

At least you know to listen to the exhaust for the noise increase from no water flow.

I had a Globe impeller once fail in a very covert way: The rubber part of the impeller started slipping on the brass core of the impeller (not the brass core slipping on the pump shaft). Because the impeller looked perfectly fine, as did the rest of the raw water system, it took a bit of time to figure out the problem. Maybe the same as your issue?

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Impeller pieces from previous service can intermittently plug up something down stream

If you have raw water cooled exhaust manifolds, I had a chunk of rusty cast iron slag about the size of a half dollar, pop loose in the manifold and block the water outlet. And I also had a similar event with the outlet from a heat exchanger, where the pencil zinc dropped off the brass cap and partially blocked the outlet from the heat exchanger.
Murphy's Law at it's best "If you think it can't happen, just wait a while and it will !!"

My 3208s had the same issue I had heard and read about...the tranny cooler had very thin passages and would clog easily...not sure why it would be intermittent...but on 3208s that was one of the "problem" areas I always was reminded of.

Murphy's Law at it's best "If you think it can't happen, just wait a while and it will !!"

As O Toole said , Murphy was an optomist!!

I have had exactly same experience as post #9, in my case it gave intermittent s.w. flow problem. I decided to change the pump impeller thinking it may have lost some "strength" in the vanes, after I got it out...or actually while I was getting it out, I found the rubber part was detached from it's hub, it must have been driving at low rpm alongside (irregular shape of the rubber i.d. acting like splines) but slipping / spinning on the hub at cruise rpm