74 on water problems

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. With the motor on a boat & the motor in the water in a normal operating position, the water pump is submerged in water. This system starts at the water intake of the lower unit indicated below.

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 or eccentric. This offset forces the water from the rotating impeller 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 of the pump housing. Here the tube is secured & sealed by a rubber grommet in the top of the water pump.

When the motor is running, the water in the water pump housing is pushed by the rubber vaned centrifugal impeller upward & into the 3/8" copper supply tube up into the powerhead.

On the photo below, the RH is a new water pump impeller. Seen here is the drive slot in the bottom for the impeller key into the driveshaft.

As said before, this is a centrifugal pump, this means that the impeller is a rubber vaned insert setting inside of a stainless steel housing. Again the impeller is offset to one side so that when the water comes into the pump housing at the widest part around the impeller & as the impeller turns the water is compressed & then forced out on the other side. This is illustrated by the LH photo below.

The above issue of reassembly has been improved considerably by this grommet being replaced by a taller one that has a more of a internal taper to it. This water pump outlet grommet has 2 side ears on the sides that hold it into the top of the water pump housing. Be sure that they are in place when reinstalling the lower unit.

The left hand photo below shows the water pump housing with a folded over outlet grommet. With this folded over rubber grommet is pushed down into the water supply channel of the tube, & the water flow is restricted. This is the most common blockage when a novice, (or even professional at times) does not get the copper supply tube inserted properly when reinstalling the lower unit after replacing a impeller. The tube needs to be round, not sharp, & greased as it is slid together during the reassembly. The grommet ears need to be secure in the pump housing.

What makes it overly hard to reassemble properly (& keep it there during assemble) is that there is not much room & it is hard to see as everything is slid up aligning the driveshaft, shifting linkage rods AND the supply tube into the top of the water pump housing all at the same time. You need to be sure the supply tube just enters into the water pump outlet grommet, then get the shifting rod aligned into the connector block. Now you may have to move the shifting lever into reverse to bring the lower unit closer to the mid-section housing. At the same time rotate the flywheel enough so that the driveshaft splines engage with the crankshaft splines all the while putting pressure upward on the lower unit.

In the photo on the right are examples of the 3 grommets that I have found, with the newest & tallest on the left. The grommet on the right is the one that appears to be shown in the LH photo of the pump housing.

Long shaft motors have a 5" fiberglas adapter plate above the water pump. In this adapter is a long rubber grommet that has a long tapered internal hole for the water supply tube to go into. When it is assembled, this longer grommet is self-aligning of the tube into the grommet, so longshaft engines have way less problems when reassembles.

Occasionally the connection of the water tube from the water pump to the bottom of the powerhead that has a rubber bushing or grommet can deteriorate & folding in, blocking or restricting the full water flow into the powerhead. This location is indicated by the red arrow in the photo below. However this grommet can ONLY be replaced by removing the powerhead from the mid-section as it fits into an adapter plate under the powerhead.

The blue arrow indicates where the main used water flow exits the block. There is another short 3/8" copper tube that diverts this warm water down, cools the exhaust tube & then out thru the relief holes in the sides of the lower unit & or out thru the prop.

I have seen different styles of these grommets on different years of motors, so they must have made changes over time. Some are just one rubber grommet, while the others that seem to have the problem are 2 smaller ones, with one on top of the tube securing flange & another on the top of the flange.

Here the older water pump outlet grommet is folded over, shown by the arrow at the bottom of the photo	Here are the 3 different grommets that I have found on short shaft motors. You can just see the ears on the center & RH ones.

If you are having trouble with water flow & need to test to see if the internal passages are blocked, I fashioned a adapter that attaches to a garden hose. This was simply made up out of fittings I had around. It uses a garden hose adapter to 3/4" pipe & then reduced down to 1/4" pipe that has a 3/8" barbed fitting. The plastic tubing is about 16" of 3/8". Then a small hose clamp rounds out the unit. You may not really need the hose clamps unless there is a actual blockage, as just the plastic tubing slid onto the copper tubing should give you some indication as if there is a passage.

Using this you should get a water stream out the pee hole & you could also get a pretty good low of water down the exhaust housing tube if the thermostat has been removed, which would be the total of the exhausted cooling water (minus the pee hole water). This flusher is not a cure all, but simply a test device, it may help remove blockages however in some instances.

One reader however wrote that he took a section of coat-hanger, cut it to the appropriate & put a slight bend in the top end. then put it in a electric drill motor & Roto-Rooted this upper folded over grommet out with success. At least he got water passage, maybe not complete & as good as if it was disassembled & done right, but for him it helped. Here the wire can not be forced to far as it will just bottom out against the block's upper cavity. This would not force anything out that may be partially blocking a water jacket internally.

Here the powerhead is removed from the cowling & exhaust housing with the arrow showing the location of the upper water tube grommet.

Note the older or square exhaust tube of the 9.9 hp

In the photo below on the left, disregard the yellow flashlight that is supporting the exhaust tube for holding it during the photo.

One e-mail correspondent fought his cooling system failure for over a year he even took it to a mechanic who tore the powerhead off & replaced the inlet grommet in the exhaust housing. Still same problem. He a year later tore it apart himself & found a partially collapsed powerhead outlet grommet. The water pump & thermostat was doing fine, just that the water could not exit the powerhead. He sent the photo on the right. This is something that can happen, but not that often. Hopefully here we can spread the word & save somebody else some aguish down the road.

Here is the actual inlet grommet in the exhaust tube & the outlet Red is motor inlet & Blue is outlet	Shown here on the left is a deteriorated plugged exhaust tube outlet grommet

Newer round 15 hp exhaust tube	This is off a 1985, notice the slight differences in the casting

Shown in the 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 & out thru the relief holes in the lower unit & or out thru the prop. 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.

The water passage first goes up & into the sideplate. Shown below is the block on the right. In the center is an plate that has holes allowing the water to get out to the outer water cover sideplate. On the left, you will notice a 3/8" hole in the bottom LH side of the sideplate cover. This is where the overboard water indicator (pee hole) hose is tapped into.

If there is a large degree of blockage at any of these holes, (this is usually not the case however) water will not get into the main motor & to the thermostat. The normal debris blockage is usually in head near the thermostat or the water jackets around the cylinder walls in the block.

This sideplate can not be removed unless the powerhead unit is removed from the mid section because there is one bolt under the RH motor mount that is impossible to get to while the motor is assembled in a running order.

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.

(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 a plugged line.

(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 new 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. If it happens that the tube from this Ell to the pee hole exit is restricted, you will have to unplug it also.

(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.

(8) Usually there will be no blockage in the block itself, 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.

(9) Is the thermostat frozen shut not allowing any water passage out of the motor? Here you will have the pee hole functioning, but the motor can overheat.

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.

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

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

Water-jacket flush adapter	Here the flusher in use verifying water to the pee hole.

Water pump viewed from bottom side	New impeller