Impeller eaten by gear oil...

Discussion in 'Outboard Maintenance' started by SClay115, Jan 22, 2011.

  1. SClay115

    SClay115 Throwin' loops

    So here is the deal, I am fussing with the boat, just getting it up and running smoothly, and notice I am not getting any water flow. The impeller in the boat is OEM Evinrude, and not more than a few months old, but still, it is in many, many pieces.

    So, upon further inspection, I note that what is left of the impeller smells like lower unit oil, which would make sense, rubber plus that lube has to spell bad news.

    Thing is, the driveshaft seal is even newer than the replacement impeller, possibly a bad seal. However, I want to address an interesting situation, which might be causing the failure. When I am reassembling the unit, when I insert the driveshaft into the lower unit, bottom it out into the gears, it wants to "pop" up an inch or two. As if there is too much pressure in the lower unit gearcase, and not enough space for it to go, causing it to rise up and make room for the pressure.

    Hopefully this makes some sense, trying to describe it is much harder with text. I am thinking that this build up of pressure is pushing lower unit oil up the driveshaft, and then onto the impeller body, thus doing irreparable damage to the rubber.

    So, here is what I am thinking, I either have too much lower unit oil, or did something wrong. I didn't have my impact driver with me, but I am thinking that if I were to open up the "fill" plug for the lower unit, insert he driveshaft, then close it again, it would allow for the excess pressure to escape, hopefully remedying the situation. Maybe? I truly think the seal is good, so I do not think that is the issue, but then again, I could be totally wrong. I am very green when it comes to outboards....

  2. levip

    levip I Love!

    id bet that might solve youre problem, my1956 fastwin does the same crap when i pull the drive shaft it wants to pop out and it does "pressurize" the gear case
    however while i was in the lu anyways id drain and refill it just to make sure you dont have water coming in
    make sense?

  3. Un-shore

    Un-shore Well-Known Member

    Yes, you are correct and also you should only fill it after assembly using the filling port and vent it so you don't put too much oil in. It expands a lot when running and could even crack your housing.
  4. cutrunner

    cutrunner Cert. Yamaha technician

    Not to try and say anybodys wrong but gear oil can not eat the blades off of an impellar, in most cases when the driveshaft seal goes bad the lower unit will stop pumping water because the gear oil is lubricating the impellar, and i slipns so freely that it does not hold the water in the housing. The only things that make blades come of are 1-cheap sierra impeller kits, 2-never changed, dryrotted, then broke,3-or it was run for a short period of time without water, and it doesnt take but 30 seconds to damage it.(imagine a rubber piece being dragged against stainless at 1000+revolutions per minute with no lube)
  5. SClay115

    SClay115 Throwin' loops

    I'm going to have to chime in here and say that if let sit long enough, gear oil, and most any other oil, can degrade a rubber product, from my experience that is. That mostly relates to the automotive and motorcycle world. My thinking was that the oil expanded, ran up past the seal, and into the water pump housing, basically soaked the impeller itself, and since I have unfortunately had to let the boat sit(move and such), the chemicals in the oil permeated into the rubber. When I went to run it again, it basically just came apart since it had deteriorated from the oil.

    I suppose I should have worded it different, my impeller blades were not "gone" they were just neatly sitting in the housing, around the metal core of the impeller itself. The seal is new, and hopefully not the issue, but in all reality, if I do need to swap it out, it really is a very short job, time wise.

    Hoping that mother nature turns the ceiling fan speed down here, and then I can take the boat out and see how she runs.

  6. topnative2

    topnative2 Well-Known Member

    water is a lubrucant to rubber and oil does degrade rubber

    make sure the splines of the impellar are going the correct direction when u install it or u will kill it