impeller on and off

[bream master]

Hi to all,about a month or so ago ichanged the impeller in my 78 35 johno,once i had changed it itook boat down to local ramp,I let motor warm up a bit,the stream coming out of pee hole was beatifull so iput motor in forward gear and i took off,everything was running fine until i noticed the water stopped flowing & motor started to overheat so i quickly shut it down.After 5min i stuck a wire up pee hole thinking its blocked or something,so i started engine up again and all was well until it done it again..........thermostat is new so to is full impeller kit,pls somebody help me.........cheers.

 

[tashasdaddy]

Re: impeller on and off

check your compression, it sounds like you are getting, back pressure into the cooling system, pushing the water back down, could have a leaking head or exhaust gasket, leaking into the cooling system.

 

[F_R]

Re: impeller on and off

Along the same line of thought, the leak could be ahead of the water pump, blowing exhaust into the pump intake side.

 

[tashasdaddy]

Re: impeller on and off

very true. but isn't it more common from the top. because exhaust is thru hub.

 

[F_R]

Re: impeller on and off

Well, the problem is we are both making educated guesses. The pump still is in the exhaust stream so if it is not sealed on the intake side, gasses will get in. Since he has been working on the pump, that raises suspicions.

While we are guessing, it could also be a problem with the grommet at the top (or bottom) end of the water tube. Low flow of water = steam = back pressure and less flow = more steam = etc.

And, that motor still has the intake on the forward side of the gearcase. How much weeds and crud in the water blocking it???

 

[tashasdaddy]

Re: impeller on and off

very true. it is time to trouble shoot.

 

[bream master]

Re: impeller on and off

Thankyou all so much for your responses.I have checked comp and all is well,running at 115psi on both cylinders,also have checked water tube to grommet no probs.I have replaced all gaskets including exhaust cleaned all water jackets e.t.c .I like you at the moment am very be-dazzled as to what this prob may be............cheers

 

[fixmyevinrude]

Re: impeller on and off

Just a thought:
I am wondering if perhaps the key for the impeller might be cracked, broken,shattered, missing or installed incorrectly. Might be worth checking out.

 

[huckelberry]

Re: impeller on and off

Just a thought:
I am wondering if perhaps the key for the impeller might be cracked, broken,shattered, missing or installed incorrectly. Might be worth checking out.

My guess also. The impeller has enough grip on the shaft to pump enough water at idle, but at high rpm it is supposed to act like a displacement pump. If the key is sheared or missing, it will slip and block flow altogeher.

 

[bream master]

Re: impeller on and off

Thanks again for all responses.Ok lets start from the beggining,the old impeller in which i took out had aslot in it in which the key from the shaft would slide in.On the new impeller in which my mechanic told me to put in, it hasnt got that slot it is different but that was what b.r.p suggested & when i installed it it fitted like a glove,so idont beleive its that prob.On idle the motor pumps water beatifully but under load she would go for about 3km before you start noticing steam come out of pee hole........cheers......

 

[tx1961whaler]

Re: impeller on and off

If your old impeller had a key, the new one should have a key. The evinrude site clearly shows an impeller with a key.
http://shop2.evinrude.com/ext/index.aspx?s1=541ec97bf3d98d1f80bbcb3fce0f9ab2

Get the correct impeller and key, and your problem is solved

 

[tmcalavy]

Re: impeller on and off

Ditto, switch back to the old-style impeller...no dis intended to your mech, but it was engineered with an impeller key.

 

[tashasdaddy]

Re: impeller on and off

get the correct part.

Part Number: 0388702
Description: IMP & KEY
Pack Qty: 1
Dimensions: 2.00 x 2.00 x 0.60 (in)
Weight: 0.06 lbs
Equivalent Parts: 0395289

 

[Cricket Too]

Re: impeller on and off

I can't even understand what would keep the impeller from slipping on the driveshaft without and impeller key. I've never heard of that.

 

[tx1961whaler]

Re: impeller on and off

"I can't even understand what would keep the impeller from slipping on the driveshaft without an impeller key. I've never heard of that."



Friction. Same reason a spun prop only slips at higher RPM......

 

[bream master]

Re: impeller on and off

Thankyou all so much for your time and effort in helping me solve this problem.I will go back to this mechanic & let him no he has wasted 40years of knowing nothing.In the mean time i will get the right impeller and key & make this mechanic pay for his mistakes..............cheers.....LIFE IS ALL GOOD IN THE LAND DOWN UNDER.

 

[bream master]

Re: impeller on and off

The numbers that tasha has stated do not show a slotted key impeller for the 78 model,it does infact show it on the 77 model,on the 78 model & higher it shows a grooved type impeller not a slotted one.Just wondering now if my motor is a 77 and not the 78 that was claimed for it to hve been.Very hard to detemine when your plate is missing................cheers:redface:

 

[fixmyevinrude]

Re: impeller on and off

Take all of your old parts with you and go back to the mechanic and show him what you need. Check everything new before you leave against the old parts. (That is assuming it ran fine with the old parts.) If you have a title you may be able to get the Model & Serial numbers off of it. Keep in mind that many times an engine is sold new (never purchased or titled or registered before) a year or more after it was manufactured. You must go by when it was manufactured and not purchased. Titles will usually state the year as the year it was first purchased in. Model & Serial numbers will show when it was manufactured. Hope it all works out for you.

 

[bream master]

Re: impeller on and off

I originally showed him the impeller with the slot in it,he told me that the current one will do no problems so i went along with him,he also said there is no way it can slide or slip up the shaft,we argued a bit & told me there is nothing to worry about..............I dont no what to beleive.

 

[McGvr]

Re: impeller on and off

Here is the real question; Is the impeller machnically locked to the drive shaft? It has to have a key, pin, or wedge? friction alone will not hold.