ohnson, Evinrude, OMC, outboard motor, outboard motor repair, 9.9, 15 hp, year of manufacture, powerhead, piston, water pump, carburetor, long shaft, 15 hp conversion, sailmaster

Water Circulations:  All outboard motors (other than aircooled) require that there be water circulation thru the motor to dissipate the heat generated by the internal combustion of the fuel.  This system starts at the water intake of the lower unit indicated below.  From there the water is sucked upward & into the water pump.  This water pump is a small rubber vaned centrifugal pump, sucking the water in from the bottom & pumping it upward into the bottom of the powerhead by way of a 3/8" copper supply tube.

Water intake on 74-92 motors	Water intake on post 92 motors

Shown below on the left is the water pump with the impeller on the driveshaft.  During functioning the water is drawn into the housing in a slot in the lower plate of the water pump, (not shown here) but this slot is at the lower side of this photo.   The vanes are not as compressed allowing the water to be sucked into the cavity.   As the impeller turns on the driveshaft, the vanes compress as the cavity is not centered but offset.  This offset forces the water out the gap seen on the top of the cavity & up into the copper tube which is located in the 1/2" round hole in the top.  Here the tube is secured & sealed by a rubber grommet in the top of the water pump.

On the right is a new water pump impeller.  Seen here is the drive slot in the bottom for the impeller key into the driveshaft.

Water pump viewed from bottom side	New impeller

Shown in this illustration below is the flow of the water thru the motor.   It first enters the motor by way of the tube in the bottom plate.  Then it goes into the RH water jacket with a slight amount allowed to go overboard as an indicator that the system is working.  The bulk of the cooling water goes on into the rest of the water cover & back out into the block.   Here it travels around the sides of the cylinder & out the top & into the water passage of the head.  Then it goes to the thermostat & out into the thermostat cover & back out into the head & then back into the lower block & out into the midsection cavity.   When in the water on a boat it then goes out thru the holes in the sides of the lower unit.

Any restriction before it gets to the thermostat will make the motor get hot.  The thermostat is near the last of line for the water to reach, because it has to be the controlling point allowing the cooler water to do it's thing for the motor before the thermostat makes contact.

Water circulation thru the motor

I  will not go into details of changing the water pump or thermostat as that is covered in the other articles, but try to give here direct pointers as what to look for if problems are encountered.   Again, though for a refresher, if you do not get any water coming from the overboard water indicator & you can not lay your hand on the top of the block for 30 seconds or so, shut the motor off before you ruin it by overheating & damaging the rings & seizing it up.

Step by Step Things to Look At:  (1) First, the water intake screens have to be clear.   (2) Next the water pump impeller has to be functioning.  Is it possible the drive key fell out when you changed impellers.  (3) The water pumps outlet grommet needs to be slid into the tube that goes up to the motor when you re-assembled it.  If this grommet got folded over when the tube was slid in, your water supply will be restricted or blocked.  This is hard to guarantee it is correct as you can not really see it when you reassemble the lower unit to the midsection after replacing the impeller.  The standard length shaft is worse, where the longshaft motors have a larger rubber guide that makes it about foolproof.

(4) Next is a hard one, as I have occasionally seen the connection of the water tube from the water pump to the bottom of the powerhead that has a rubber bushing, deteriorate & folding in, blocking or restricting the full water flow into the powerhead.  This however can only be repaired by removing the powerhead from the mid-section as it fits into an adapter plate under the powerhead. 

(5) The next place the water will be seen is at the overboard water indicator, otherwise known by many as the "pee hole".  This will not be had on the 74-76 motors as described previously.  This rubber tube comes from an ell fitting in the lower section of the RH water jacket & is directed to a plastic fitting on the outer upper RH rear section of the lower cowling. 

This rubber tube is slid onto a plastic fitting that has a small hole to the outside, allowing a small stream of water about the size of a wooden match to be observed as an indicator that the water pump is functioning.  However since this hole is small, it can get plugged with debris if the motor has been ran in dirty water, or a bug has crawled up inside & died.   It may be a good idea to keep a small wire handy that can be poked up inside this indicator hole to dislodge any debris if that is the problem if it does not spray water. 

The post 93 motors have the tube come from the top of the water jacket & do not use a plastic outlet, but merely use the rubber tube itself protruding slightly out the back.  This makes for a very simple way of pulling it out & checking the hole.

(6) Another thing, that I describe below is where I have had to drill a 3/8" hole thru the sidecover in alignment with the center of the outlet Ell.  From here I drilled the plastic Ell  & tapped it to an 8-32 thread.  Now I made a short (1/8") threaded 8-32 screw that was screwed into the Ell as a plug when the motor was running.  This motor apparently had internal debris inside the water jacket that occasionally plugged the pee hole.  But poking a wire up inside the pee hole did not gain me anything.  Now I could go thru the sidecover hole, remove the screw, & run a wire into the actual Ell & the water jacket also, thru the threaded hole & with the motor running, it would blow larger chunks of debris out.   This allowed me to clean the plugged fitting from the outside.   The small hole on the sidecover was inconsequential.  Shown below by the red arrow is this hole.  Be careful to not over tighten the plug screw in the plastic.

For you non machinists that don't have taps or understand a screw size & threads, here is a simpler method of doing the same as above.  Drill the 3/8" hole as describe above, hut get a #8 or #10 stainless sheet metal screw.  Drill the hole in the corner of the plastic Ell to a size smaller than the screw.  Start the screw in the Ell to get the threads initiated.   Remove the screw & cut off the screw threads so that there is only about 1/4" or less of threads showing.  Now, you can run the motor to allow the water pump to BLOW any debris out the hole you have created.   Screw your plug screw in & see if it is now "Peeing".  If not then pole a wire up the pee hole from the outside to free anything plugging it up.  You may have to repeat this a few times to get all the crap out.  But it is better to take some time doing this than to burn a motor up, thinking it was OK.

(7) Next the water flows around in the sidecover.  If there is any salt corrosion here it will effect the cooling as it blocks or restricts the flow into the block.  This cover can not be removed on the pre 93 motors without removing the powerhead from the midsection as there is one bolt under the RH motor mount that is impossible to get to.

Usually there will be no blockage in the block itself, (8) but very often there will be in the head & quite likely in the thermostat itself.  The simple thing here is if there appears to be a problem, take the head off, & remove the headgasket as water passages on both sides of it need to be checked.   Once the water gets thru & past the thermostat, you should have no problem.

At times I have seen when the motor is run on muffs, water bubbling out of the shifting rod grommet at the lower mounting area.  Any of the above blockages could be the reason the water is bubbling as it may be backing up into the water pump & being blown out of the water pump outlet grommet.

It is highly recommended that after a day of fishing in saltwater that you run it with muffs.  If it is the post 93 series, then there is a FLUSH fitting on the upper front RH water jacket.   This is not for running the motor, but for a non-running flush.  

There is also a couple of anti-salt solutions, one being Salt-Away.   These chemicals when used as a flush are designed to neutralize the salt residue left in the motor if it was ran in saltwater.  Here you mix a portion of the solution with water & run the motor, when warm shut it off with the solution still in the motor.

A  self-contained flushing unit using a live-well pump

For those of you who only fish freshwater, you do not realize how fortunate you are.

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 Copyright © 2007 LeeRoy Wisner  All Rights Reserved

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Originally started 01-20-2007, Last Updated 05-29-2008
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