Cooling Question

[phoodieman]

1967 40 HP RDSL 29E

The manual says, "At low speeds the impeller works as a displacement pump. At higher speeds water resistance keeps the blades from flexing and the pump acts as a circulator, enough water being provided by the forward motion of the motor through the water".

So if I'm reading this right, at low rpm I should have cooling water discharge from the back of the motor, but at higher rpms (and speeds), there shouldn't be any water coming out of the back of the motor. Because at speed I'm not seeing any water coming out of the discharge.

Is this how the motor should operate?

Phoodieman

 

[oldcatamount]

Re: Cooling Question

You should see a "spray" of water at all speeds. Less intense at idle but very visible at high speed. You should be able to see this spray by simply glancing back there. If you have to keep looking for water, the pump is probably failing.

 

[phoodieman]

Re: Cooling Question

I took the boat for a ride yesterday with a buddy so I could watch the motor at high and low speeds. At idle I had water coming out, but I wouldn't describe it as a "spray". At higher speed I didn't see any water being discharged. I wish I had replaced the impeller when I had the lower unit off. It looked like it was in good shape, but after reading a couple of other posts I guess I need to replace it and get the water discharge all the time. I have had a couple of issues I was dealing with and now it looks like I might have been over heating the motor. May be an impeller replacement will clear them up.

phoodieman

 

[oldcatamount]

Re: Cooling Question

If you do take the lower unit off to replace the impeller, be sure the grommet (that receives the copper water line at the impeller housing) is in good shape and the copper line is all the way "up" inside the upper grommet to.

 

[kfa4303]

Re: Cooling Question

hi phoodieman. I have a '66 33 hp which is essentially the same as yours. you definitely need a functioning impeller, or you risk serious damage to your motor. your impeller may have been good, but reinstalled improperly after you inspected it. either way check/replace it again. it's well worth the peace of mind. once it is replaced, you should see a discharge (spray,mist,sputtering) of water mixed with exhaust out of the leg of the motor at ALL times when running. also, the motor can only be run in the water and/or in a tank with water up to just an inch or so below the exhaust port. you cannot run these guys on the "muffs" you see other motors use. the amount of spray and exhaust should increase as the motor is run at higher rpm. the impeller/water pump is driven by the prop shaft. as the motor spins fast so to does the water pump which causes it to suck in (impel) more water. that water is then directed up a copper tube to the underside of the engine where the water splashes against a metal plate to cool the engine. the now warmed water is "spit" out of the back of the motor along with the exhaust. this will cause some oil/smoke to accumulate in your test tank, but that's normal.
oldcatamount is right to warn you to make sure that the copper tube is properly seated on the water pump housing and up to the underside of the motor. they can often become dislodged when servicing the lower unit. if the tube is not connected properly, your impeller may still be working, but the water may not be reaching its proper destination. also make sure that the impeller key is in place. if it is not, or is broken the prop shaft can spin, but the impeller will not. as a result, no water will be pumped. make sure you're using the proper fuel oil mix. it should be 50:1 although some folks run 24:1 to be safe. check these and let us know what happens. here's a link to a video of what type if "spray" to look for. your motor is a little bigger, but it gives you an idea of what to look for.

http://www.youtube.com/watch?v=6tPc3SkIX2g