Inboard impeller question - fried or not???

C

cacioa

New Member
Nov 16, 2010
55
Huntington, NY
Boat Info
2002 340 SUNDANCER, RAYMARINE C120
Engines
8.1s
My boat was launched this weekend. Once in the water, I started it up and went to pay the hauler. When I was going back to the boat I noticed no water coming out of my port exhaust and started noticing some smoke. Temp hit around 160 and I shut it down right away. I checked the strainer and it was dry. I then put a bucket of water in the strainr and it primed the impeller fine. I then proceeded to my slip around 20 minutes away at 5-7 knots. Temp was fine all the way and exhaust was pumping like normal. Not too sure if I damaged the impeller or if i caught it in time. Basically it ran for around 5 minutes dry. I have a 2002 340 with 8.1S wich have the guardian system but no alarms went on. Any info, advice, thoughts or even precautionary actions I should take at this point would be appreciated.
Thank you
 
You may have lucked out this time.....I hope so, Mike.
 
In my exhaustive research, 30 - 60 sec is the life span of an impeller out of water.

#1 I'd at least look at it to check for damage
#2 what caused it to not work right away, my first hunch is the 'key' that goes on the impeller to shaft may be missing, causing it to not spin, but when you added water yourself to the system, it gave it enough lubercation to spin just enough to have water flowing, and keep the temp down. If thats the case the impeller will be hit or miss and eventually just not run anymore.
 
cacioa said:
..... I checked the strainer and it was dry. I then put a bucket of water in the strainr and it primed the impeller fine.....
Click to expand...

May I ask what kind of trick is that? If you have an issue with raw water passing the seacock and getting in to the seastrainer, how will a bucket of water resolve it?

Although, I think that 30-60 seconds is kind of an extreme, but 5 minutes is a long time and I'm almost positive that the vanes have lost some surface. At the minimum I would take it apart to have a close look. But, since you have it in your hands already, why not just install brand new one and keep this one as a spare? Having 100% functioning cooling system on the marine engine is more important than having a fresh oil.

However, before even doing anything with the impeller I would make sure that whatever is blocking the raw water from getting in to the seastrainer is cleaned and there's good water flow. You might have picked up some ealgrass or seagrass, a plastic bag or some other object in the scoop strainer.

Last weekend my dock neighbor came back on one engine, b/c he sucked an eal via his IPS drive (on Formula). What a mess, I was totally shocked to see how poorly Volvo designed the intake system. The impeller is installed BEFORE the seastrainer. :wow:
 
Thank you all for the advice. I'm going to play it safe and change it out. At a minImum, I'll take a picture of the impeller to show what it looks like after 5 minutes of running dry.
 
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One more thing to look at when it comes to diagnosing impeller/overheating issues....when i took delivery of my used boat, I installed new impellers on the engines and genny. Some maintenance log items were not recorded well in the last few years of the previous owner so for peace of mind.....
Anywho.....the genny worked fine for awhile, and then overheated. I figured that somehow I had burned the new one, so I went and bought another and proceeded to replace it. The used impeller was just fine, and the problem was that sometime in the past, a unit had come apart and chunks of rubber vane left the hub and had blocked the pump outlet (jammed inside the port) and up the hose into the heat exchanger, causing more blockage.

I'm not suggesting this is your issue, but whenever a new impeller is installed (especially on a previously enjoyed boat), it would be a good idea to look deep into the pump assembly for any loose parts. Seems that more than a few impellers have been run dry on many a boat.
 
Toecutter said:
One more thing to look at when it comes to diagnosing impeller/overheating issues....when i took delivery of my used boat, I installed new impellers on the engines and genny. Some maintenance log items were not recorded well in the last few years of the previous owner so for peace of mind.....
Anywho.....the genny worked fine for awhile, and then overheated. I figured that somehow I had burned the new one, so I went and bought another and proceeded to replace it. The used impeller was just fine, and the problem was that sometime in the past, a unit had come apart and chunks of rubber vane left the hub and had blocked the pump outlet (jammed inside the port) and up the hose into the heat exchanger, causing more blockage.

I'm not suggesting this is your issue, but whenever a new impeller is installed (especially on a previously enjoyed boat), it would be a good idea to look deep into the pump assembly for any loose parts. Seems that more than a few impellers have been run dry on many a boat.
Click to expand...

You definitely made a good point, but based on this statement "...I checked the strainer and it was dry. I then put a bucket of water in the strainr and it primed the impeller fine...." I think his issue is before the impeller. Now that the impeller ran dry for a while OP will change it to play safe, but it's not going to resolve the issue. The raw water flow from the seacock cannot be stopped by something like an "air pocket". Remember that there's quite a lot of pressure pushing that water thru. So, if it's not getting in to the seastrainer and then to the impeller there must be some physical object blocking it.
 
Reviving a somewhat older thread: My generator stopped discharging water out the pee hole/exhaust so I shut it down. Opened the strainer and found it clean, opened the sea-cock and had a small flow filling up the strainer housing. Tried starting the generator again and still no water flow so shut down again, next step is to check the impeller but was wondering if I should try blowing from the sea-cock back out to make sure the line is clear. Any pointers?
 
Thanks wow not easy to get at :smt100 Had to pull off one of the cooling lines to the heat exchanger just to get at the impeller and of course one side is a ***** to get at. Will order the parts today.
 
mrclark321 said:
Reviving a somewhat older thread: My generator stopped discharging water out the pee hole/exhaust so I shut it down. Opened the strainer and found it clean, opened the sea-cock and had a small flow filling up the strainer housing. Tried starting the generator again and still no water flow so shut down again, next step is to check the impeller but was wondering if I should try blowing from the sea-cock back out to make sure the line is clear. Any pointers?
Click to expand...

Based on the slow flow rate from your sea-cock to the open strainer, I'd say there must be some restriction/obstruction somewhere from the intake fitting to the end of the hose attached to the strainer. Either a shot of compressed air or water from a hose might dislodge whatever is blocking it. If that doesn't work, remove the hose from the sea-cock and visually inspect the inside of it and open the sea-cock briefly to see what kind of water flow results. You can also shoot water with a hose into the raw water line and see if the flow to the open strainer is restricted.

With your reduced flow rate mentioned, it seems unlikely that your issues would be caused from a bad impeller.
 
Thanks Jim I diconected the supply hose to the strainer and blew it back through the sea-cock and it seemed OK, I took the plate off the impeller but could not see it as there was a hose in the way and did not have the tools to remove it. I ended up picking up a couple impeller kits and hope to tackle it tomorrow. Need to hire a midget to give me a hand as there is no damn room to move around. :smt013
 
Nehalennia said:
Replace it. It's cheap peace of mind.
Click to expand...

I'm with Todd,

About three years ago, I was training my then 13 year old son on monthly checks - he cycled the stbd seacocks and I cycled the port ones, I didn't check his work - my mistake. 5 minutes at idle later, and a water pressure alarm. I asked him - "did you reopen the seacock?" and his answer was priceless - "I'm not sure".

So he learned how to change his first impeller (with supervision) - it looked brand new, but I didn't even keep it as a spare - $30 and 1 hour of work - it's not worth risking it.
 
Well this morning and afternoon for quite a few hours I think I got it fixed. The impeller was disintegrated only leaving the collar that seemed to be seized on so this involved removing the pump and most hoses and flushing all lines as there was pieces of the impeller everywhere including the heat exchanger. After finally getting everything back together and firing up the generator all apeared good until steam started to come in the coolant tank....DOH did not add enough glycol/water so had to add more and vent the system. After that the generator was started again but for some reason it was hunting and tripping the breaker. :huh: I then shut off the hot water heater and air conditioner to reduce load and things seemed fine, let it run for another 10 minutes checking water flow out exhaust and for leaks on the cooling lines which there were and adjustments were made. After some time I added the water heater and air conditioner and the breaker did not trip so hoping everything is OK.
This was an attempt at my part at doing this job myself to save a few bucks as well as just get to know the boat better, as for the time it took to do the job I was way off. The joys of owning a boat :grin:
 
The fixation seems to be on a blockage before the seawater pump. That doesn't necessariiy have to be the problem. Anytime you truck an inboard cruiser, and leave the seacocks open, the air flow over the hull can suck the water out of the intake system and leave the strainer and lines from the intake to the impeller completely dry. Sometimes these boats will self prime, others may not depending upon the plumbing and elevation of the water lines in side the hull. When an air lock is created or the distance is just to far for the seawater pump to pump, your only option is to prime the pump as the OP did when he poured a bucket of water in the strainer. If I haul out and am on the hill for a week, my generator drains itself dry and I have a hose fitting in the lines ahead of the strainer to purge air and prime the gen pump.

If smoke came from the exhaust, the impeller may be functional, but t he vanes aredamaged and will break off sooner rather than later.........go ahead and change it now.
 
mrclark321 said:
Well this morning and afternoon for quite a few hours I think I got it fixed. The impeller was disintegrated only leaving the collar that seemed to be seized on so this involved removing the pump and most hoses and flushing all lines as there was pieces of the impeller everywhere including the heat exchanger. After finally getting everything back together and firing up the generator all apeared good until steam started to come in the coolant tank....DOH did not add enough glycol/water so had to add more and vent the system. After that the generator was started again but for some reason it was hunting and tripping the breaker. :huh: I then shut off the hot water heater and air conditioner to reduce load and things seemed fine, let it run for another 10 minutes checking water flow out exhaust and for leaks on the cooling lines which there were and adjustments were made. After some time I added the water heater and air conditioner and the breaker did not trip so hoping everything is OK.
This was an attempt at my part at doing this job myself to save a few bucks as well as just get to know the boat better, as for the time it took to do the job I was way off. The joys of owning a boat :grin:
Click to expand...

Excellent you have learned a lot about your boat I have asked a lot of questions of a quite a few mercruiser mechanics the more you know the easier it will get to do a lot more work on your own. Now maybe you can start doing some preventive maintenance like every time you get in the bilge to check fluids spend some time looking at everything for leaks take a screw driver tighten all the clamps you can check all grounding wires for corrosion and if there tight. I do this almost every time I'm in the bilge you'll be surprised how many clamps come loose from vibrations and you'll get to know all the different quirks of your boat and save some boat bucks in the future.
 
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