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

Note -- some of these articles have pictures that require a possible long load time, especially if you are on a dial up connection

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 provides a unlimited water cooling source. This system starts at the water intake of the lower unit blue arrows indicated below. The red arrows are the exhaust water being dispersed out of the motor.

Do not run the motor even for a few seconds without water to the water pump. This could be while you are testing it ashore on muffs or in the water if the motor is tilted up. Remember to lower your motor from the up traveling position when you launch your boat. Other than it being loud, it will also ruin the water pump impeller.

Below is research done using Mercury motors, others should be nearly the same as the water pump impellers are very similar for all outboards.

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 outer edges of the vanes are not the only significant part of the water pump impeller as the circular rubber rings on both sides also act a seal, keeping the water trapped between the vanes.

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.

The issue of reassembly of the lower gearcase back to the exhaust housing after a water pump impeller has been replaced has been improved considerably on these motors by the water pump outlet 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.

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.

I have seen different styles of these grommets on different years of motors, but never had a clear vision of which was for what until I looked at a Bombardier water pump kit, here it shows each grommet, the part number & for what it fits. All of these grommets are secured into the top of the water pump body by a set of "EARS".

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.

You can also tell if the head gasket, or exhaust gasket is leaking by removing the spark plugs, and if one of them is leaking, water will come out of the plug holes.

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 too far as it will just bottom out against the block's upper cavity. This however 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 at the upper end of the water supply tube.

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 who reads this article 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 in the middle below. Why the mechanic did not catch the other bad grommet is a mystery. 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.

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 on the left 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 exhaust (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.

Here is the actual inlet grommet in the exhaust tube & the outlet Red is motor inlet & Blue is outlet	Shown here on the upper left is a deteriorated, partially plugged exhaust tube outlet grommet. It should look like the inlet grommet on the bottom right

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

In the RH photo below, there obviously was no water entering the block & from the whitish debris it is obvious the motor was a salt water motor that probably did get flushed enough. The LH photo had minimal water entering the engine but none leaving so essentially both motors were overheating & had no tell-tale water exiting the motors.

Totally almost blocked inlet water grommet & totally blocked outlet grommet	Here is another bad situation with a clearer photo, where the water inlet (lower RH) is totally blocked & the outlet (upper LH) is partially blocked

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 "tell tale" indicator that the system is working. This overboard water indicator is commonly called the pee hole by many outboarders. The water coming out of it will not be hot because it has not had time to circulate thru the block's water jackets. It may be slightly warm but probably not enough for you to really tell if your put your hand in it. It may be slightly warmer before the thermostat opens allowing more water to flow thru the motor.

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 to the lower cowling/exhaust housing.

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.

You can "smell" and "feel" an overheat condition. You can also buy a "temperature stick" that works like a crayon. You place a stick mark on the head and run the motor. If the stick melts, it's too hot. These sticks come in various temp ranges so you need one for the temp range of your engine.

(1) First, thing you should do if no water is coming out, is to poke a wire or weed eater cord up in the overboard indicator (tell tale) to dislodge any debris there. I have seen small bugs build nests in there.

(2) The water intake screens in the sides of lower unit have to be clear of any debris.

(3) Next the water pump impeller has to be functioning. Is it possible the drive key fell out when you changed impellers.

(4) The next place the water will be seen is at the overboard water indicator, otherwise known by many as the "tell tale". 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 or a section of the Nylon weed eater cabel 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.

(5) The water pump's 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.

(6) If you are absolutely sure that the water pump is good, and the passages are clear, then possibly there is a blockage at the plastic elbow on the other end of the tube that goes into the water jacket on the motor. The way things are put together, you can not get to the lower front bolt to remove this cover plate without complete powerhead removal.

I have eye-balled the location of this elbow & marked on the outside of the lower motor cowling, then drilled a 3/16" hole thru this cowling. Then if needed to enlarge it to be more in line with the elbow & allow the screw head to enter the hole, use a Dremel tool & a 1/8" burr to enlarge it in line with the elbow center. Now drill out the center of the elbow with a #29 drill & tap it to 8-32 threads. You can now use this hole to poke a wire directly into the water jacket on the motor & possibly clean out other debris. Then get a 8-32 round head brass or stainless steel machine screw 1/2" long, thread a nut onto the screw so you have about 3/16" of threads showing & silver solder or epoxy the nut in place. If you need to make the nut smaller to get it in your hole, grind the corners off or lathe turn them. You can simply just shorten the threads & allow the head of the screw to bottom out on the outside of the elbow, but trying to get this short screw in this confined area is hard for big fingers. But be sure you do not let it go so deep that it blocks any water from exiting the telltale hole. Use this screw to plug the elbow after the debris has been flushed out.

You have a small access hole (3/8" or so) in the lower cowling, but that is a lot better than the hassle of removing the lower unit & then the power head just to get the one bottom bolt of the side cover off.

In the motor shown below, the water flow out the telltale was erratic, no amount of poking with a wire would help. I knew the water pump was fine because just before it plugged the water pressure blew the hose off the elbow because I had forgot to use a tie tape to secure it. And with no water coming out, the motor never overheated. But I wanted to sell this one, so this was the solution. After starting it with this hole in the elbow, some water came out, but poking with a wire dislodged debris giving the steady stream shown in the photo below on the right. It plugged a few times, & more wire poking finally got enough of the debris out that it ran for a few hours in the test tank with no other problems.

Shown below on the left by the red arrow is this access hole. Be VERY careful to not over tighten the plug screw into the plastic Ell. It may be better to loose a screw than to strip out the plastic elbow & then have to pull the powerhead to replace it.

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 poke 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, or remove your plug screw & let the water pump blow out any other debris again.

It is better to take some time doing this to be sure everything is OK than to burn a motor up, thinking everything was fine.

(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 tell tale hole functioning, but the motor can overheat.

(10) Next is a hard one, as I have occasionally seen the connection of the water tubes to & or from the water pump at the bottom of the powerhead that has 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.

To check for this, I would first pull the thermostat & see if it is functioning. While it is out run the motor for a bit to see if the pump is working, you will get water all over, but at least you will know. Then possibly pull the head & check for water passages thru the headgasket are clear. While the head is off check the water jackets around both cylinders & remove any debris is found. Reassemble without the thermostat & run again. If it still gets hot then it is a pretty good bet that the water outlet grommet out of the block is deformed or plugged.

(11) If you did not get the motor shut down in time when the impeller failed, seizure is not always the end of the world for a SMALL outboard. Usually they will free up when they cool down and aside from scoring on the piston there is usually little damage. These little motors are tougher than some people think. Most time after it cools down it will start back up again. However do not run it other than to see if it starts until you replace the impeller. It also wouldn't hurt to do a compression check to be sure everything is still OK

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

Here a short shaft water pump outlet grommet viewed from the top, is folded over, almost totally restricting flow, shown by the arrow	Here are the 2 different grommets that I have found on short shaft motors. You can just see the ears on the center & RH ones. The one on the right is shown in the photo on the left

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

Here is the location of the drilled hole in the lower cowling & the plug screw	Here is the motor running with the new plug screw removed. At a higher RPM, water squirted over 6 feet.