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My boat started to overheat last weekend. I pulled raw water pump out and it was shredded so I replaced it and tried again and the boat overheated. I rechecked the raw water pump and I found a piece of the old impeller that got away from me. So now I went ahead while I was at it and replaced the thermostat and engine water pump as well. Yesterday I took it out and it overheated again! This morning I pulled the raw water pump again and the impeller is in good condition but there was what appears to be ground up rubber in the line. I put the muffs on and tried running water through the line but none was really making it from the outdrive to the water pump. Any ideas? Yes I will try to flush the line but why small rubber looking pieces? BTW I have a 2003 mercruiser 350 and bravo 3.

Thanks

So out of curiosity, whens the last time you replaced the impeller? Its a two year maintenance item, but 1 year if you suck up dirt or sand often. You've now created a PITA situation for yourself because pieces of impeller vanes go through the whole exhaust (risers/manifolds/water passages in head/block) and clog the waterways. They are very challenging to get out most the time. It took me from March- end of July to fish out 3 pieces in my 4.3l from the last owner!

You need to backflush the system and pray the pieces of impeller come out. Have you taken the thermostat housing off again? Rubber gets in all of the passages. Take off the lower hose of the circulating water pump on the front of the engine. You might have to do this several times as the rubber pieces circulate and find new "homes" in your engine/cooling system. Thats the easy part - if you keep on overheating and your thermostat housing, hoses, etc. are clear the risers and manifolds might have to come off so you can probe out the impeller pieces.

This is a lesson to check the impeller every year and change it, no matter what, every two. Period.

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1997 Four Winns Vista 278
T - 4.3l EFI
Kohler 4esz Genset
379 hours as of 8/8/21

Welcome gerard, those small rubber looking pieces are old impeller vanes. When you say your impeller was shredded, do you mean no vanes left on it, a couple left, or a couple gone? Try and account for any vanes that are gone from original. It is a pain hunting for them for sure, but worth it $$$$ wise....

Technologic80 has good advice (if a somewhat rough way of saying it), also you may have luck by taking each hose off and blasting water thru them with a garden hose, make sure to observe to see if any peices of impeller come out too...

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1996 205 Sundowner DLX
5.0FL Volvo SX Cobra
Tow Veh: 2012 Nissan Frontier Pro-4X

Yeah, sorry if I sounded rough - I get very frustrated because the impeller is so easy to replace and cheap, to boot!!! $30 every two years guarantees no little rubber pieces blocking tiny passages throughout the engine and manifolds and likely the chance of never overheating.

Some people even remove the impeller over layup (winter) so it doesnt take a set in the impeller housing. Ive read of some people taking the impeller out, putting silicon lubricant on it and re-installing it for layup. Now, I dont go that far but I check it annually and replace it bi-annually no questions asked.

Can I be re-named the forum impeller enforcer?

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1997 Four Winns Vista 278
T - 4.3l EFI
Kohler 4esz Genset
379 hours as of 8/8/21

The impeller-nator...

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1996 205 Sundowner DLX
5.0FL Volvo SX Cobra
Tow Veh: 2012 Nissan Frontier Pro-4X

Yep the impeller is one of the most important maintenance items on the boat, be it an outboard of stern drive. I always take mine out and inspect it, on the OMC Cobra the are pretty durable and can last 2-3 seasons depending on your conditions. Any wear at all on the ends of the vanes or the wear plate and I change it. I have 2-3 spare ones on the boat already installed in the housing, I can swap it I about 15 min..

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

It's okay that you were rough on me. I am in that Army and can take anything you throw my way Also I didn't make known to you the fact that I bought this boat just last month and am now going through it with a fine tooth comb.

After I posted the question I pulled the impeller out again (which was the new one I just put in last weekend) and found a piece of the plastic that is on the inside of the impeller and wraps around the shaft buried under the new impleller. Apparently it was hidden in between the housing and the shaft oil seal and worked itself loose and the new impeller had three groves worn in it and that is where the ground up rubber was coming from. I have since replaced it with a new impeller and flushed out all the lines as much as possible. Hopefully next time I can launch it I will have sucessfully fixed it!

We just had to replace the entire pump. Dealer looked at the housing & said it was completely worn from sand. Previous owner boated exclusively in the Mississippi. Brass & sand don't mix. $386 pump later & overheating is no longer an issue. Dealer said impeller should be replaced every year but in most cases every 2 years is ok.