Logo
FULL SITE MENU

Tohatsu 9.8 cooling problem

C

Chick12

New member
Recently, I made a mistake that has screwed up my 2018 Tohatsu 9.8 four stroke (with less than 50 hours on it). After using the motor in salt water I attached the flushing tool to a garden hose and flushed the motor. Unfortunately, when I removed the flushing tool I forgot to replace the screw in the lower housing. The next day I ran the motor for about 20 minutes before noticing that the "pee" stream was not working. I shut the engine off, discovered and replaced the missing screw, but was unable to re-start the motor until a half hour later. When it finally restarted, there was no pee stream (which is usually pretty strong). I thought maybe the impeller had broken apart, but it still seemed in pretty good shape. I replaced the impeller anyway. On starting the motor, it seemed to be pumping strong, but no water exited the pee hole. There was lots of water, however, flowing out of the lower housing. (I haven't taken the housing apart to see exactly where it's coming from.) I again removed the lower unit and connected some plastic tubing to the metal uptake tube and pumped water into it. I also opened up the thermostat housing. No water came out of the thermostat housing or the pee hole; but still lots of water pouring out of the lower housing. I looked up into where the uptake pipe connects to the power head and that seems to be firmly attached. In summary, something seems to be blocking the flow of water. Any suggestions as to what the problem is or what else I can do to diagnose??
Bernard
 
You may have gotten pretty hot with the flush plug out; however, that should not damage the impeller; it would just bleed water off before going up to the motor.

First, if an impeller needs replacement, do a complete wp kit, not just the impeller. It will pump better and last longer.
Next, you won't get water through the thermostat when it is closed.
Then too, any crud in the pee tube will keep it from peeing even if pumping well. While running, push a stiff monofilament or wire into the pee tube a few times to dislodge any crud in there.
 
pvanv said:
You may have gotten pretty hot with the flush plug out; however, that should not damage the impeller; it would just bleed water off before going up to the motor.

First, if an impeller needs replacement, do a complete wp kit, not just the impeller. It will pump better and last longer.
Next, you won't get water through the thermostat when it is closed.
Then too, any crud in the pee tube will keep it from peeing even if pumping well. While running, push a stiff monofilament or wire into the pee tube a few times to dislodge any crud in there.
Click to expand...

Thanks Paul. But I don't understand why the water I pumped into the uptake tube would not come out the thermostat housing after I removed the thermostat.
 
I removed the apron from the lower unit, started the motor, and took the attached photo of water discharging from the motor. (I'm not sure what that hole is called from which the water is discharging.) While it seems to be pumping fine, no water came out of the pee hole, but I could feel puffs of air coming out. After running for a couple minutes the motor was hot to touch, so I cut it off for fear of overheating. Still seems like there is some kind of obstruction somewhere, but it is definitely not the pee hole or the hose that feeds the pee hole.

20190426_185204 (640x480) (2).jpg
 
If you are getting puffs out of the pee hole, you are not pumping properly. Review the water pump installation again. If the water pipe is not seated correctly, your pump will fill the exhaust housing, but not pump up into the power head. You can check for 150F on the power head with an IR thermometer.
 
Question: When changing the impeller, it is slightly larger diameter than the stainless housing into which it must be squeezed. As a result, the fins on the impeller must be bent one way or the other in order to squeeze it in. Does it matter which way the fins get bent (clockwise or counter clockwise)??
 
Yes impeller vanes are curved when installed.----Note that shaft is offset.-----Note that the volume between vanes changes as shaft rotates.---That is how the pump works.-----I always put impeller on the shaft first.------Then lower the pump housing while rotating the shaft.-----That method ensures that vanes are correct !!
 
racerone said:
Yes impeller vanes are curved when installed.----Note that shaft is offset.-----Note that the volume between vanes changes as shaft rotates.---That is how the pump works.-----I always put impeller on the shaft first.------Then lower the pump housing while rotating the shaft.-----That method ensures that vanes are correct !!
Click to expand...

Thank you, Racerone. I don't quite follow what you mean by the shaft being offset. In any event, when I slipped the housing down over the impeller (using a new kit) it seemed to me that the impeller vanes were flexible enough that they would change direction, depending on which way you turned the shaft. So I wonder if they really stay oriented in the right direction when the shaft is turning at 1000's of rpms. Anyhow, I put things back together and the mystery continues: no water coming out of pee hole; head temperature well over 200 degrees F. I guess I'll pull it apart and try again to get the vanes pointing toward the discharge hole.
 
Sorry----These pumps are elegantly simple.-----Hard to assemble them wrong.----Do not overthink this.-----I do not believe the water pump itself is your overheating problem.
 
The vanes will flip into the correct direction as the motor runs.
Sounds like the water pipe is not seated in the pump outlet.
 
Thank you Paul and racerone for hanging in on this issue. It does seem like there's an obstruction somewhere, and it seems like the tube would be a likely location. However, when I removed the bottom unit, the tube disconnected from its lower terminus and remained fastened at its upper terminus. And when I reassemble things it looks pretty clear that the tube is reinserting properly into the lower terminus. In addition, wouldn't an obstructed tube result in no water being pumped out of the other discharge points on the motor, such as the one shown in the photo attached previously? Or could there be some other way that water driven by the impeller finds its way out of that discharge point? (Racerone, I came across an unexpected source of information that presented a very clear explanation/illustration of what you referred to as the shaft being "offset." In Alaska, there is an educational program directed especially at indigenous people who often live in very remote locations. These people depend heavily on rivers for transportation and need to have practical knowledge of how to fix their outboards under trying circumstances. As a result, part of the curriculum posted on-line explains how outboards work, including details about impellers. I wish schools in the lower 48 offered such useful materials. Located at http://www.ankn.uaf.edu/publications/vs/cooling.html .)
 
I am 100% sure that you can find a " small engine repair course " at many high schools in the big cities.---Night school they used to call it.--Well worthwhile taking such a course , cost you say 1 hr shop time to save yourself many times that amount !!
 
Removed hose from pee hole back to exhaust cover; no blockage. Air pulsing out of pee hole, but no water. Puffing also from idle exhaust port cover, but no water. Removed thermostat and tested in hot water; it opens okay. Also ran engine without thermostat; no water discharged.
 
The "air" that is coming out is actually exhaust. All that water coming out of the side drain looks like the pump is not connected to the water tube. Is the grommet in the water pump housing for the water pipe to seat into? If not, you are just pumping into the exhaust housing... not up into the power head.
 
Removed lower unit. Grommet is in place and pipe seems to fit perfectly when upper end of drive shaft seats in place. I tried a little experiment doing a reverse flush: 1) Removed pee hole hose from where it attaches to exhaust cover. 2) Attached to the exhaust cover a piece of tubing of same diameter and adapted the other end of the tubing to connect to garden hose. 3) Turned on hose and water exited exhaust housing and water pipe that had been disconnected from impeller housing. 4) Removed thermostat housing and saw that water was making its way to the thermostat housing. 5) Since water seemed to flow everywhere it was supposed to (albeit, in a backward direction), I figured there could be no obstruction in the entire system. 6) Put everything back together and ran it in the tank. 7) Head quickly reached 200-plus degrees, and no water coming out the pee hole. 8) Any ideas on how this could be??
 
Clearly, you are not pumping. The puffs are exhaust. Did you perchance leave the key out of the impeller. That is what the drive shaft uses to turn the impeller. Still then, you would not expect water coming from that side drain if that were the case.
 
Took everything apart again and verified that assembly matched what is shown on the parts diagram. Checked that key is in place and turned drive shaft to verify that impeller turns as shaft turns. Put everything back together and started it up. Water comes out of side drain but, once again, nothing from pee hole, and head overheats. I've never been more discouraged about anything. I keep thinking it must be something simple, staring me in the face. I think back to when this started: operating the engine for 20 minutes without the flush plug in place. When I replaced the flush plug I hoped it would start pumping again, but it didn't, and I started down this path of replacing water pump parts.
 
H.. If the water pipe broke off below the power head, you could possibly get those symptoms. Never seen it, but look at it this way; the exhaust puffs show you are not pumping through the head, yet the water coming out the drain hole shows that you are pumping into the exhaust housing.
 
In peeking up there, it seems to be attached pretty firmly. I can't figure out from the parts diagram what path the water takes after it exits the tube. Does it enter the power head, and is there any way to access to what's beyond that point without taking apart the power head?
 
It goes right in. There is a grommet there, and the tube is held in with a clip that has a bolt through it.
 
Started it up again. At first, it looked promising. Water coming out of exhaust side hole and also out of pee hole. Less than a minute later the pee hole flow diminished and eventually only exhaust gas out of pee hole. Also, head quickly heated up to 230 degrees or more. However, when flow from exhaust side hole is plugged, water then comes out strong from the pee hole, and head temperature quickly drops to more acceptable range. Unplug exhaust s
 
Further thought on this: It all started when I ran it in Florida Bay without having screwed the flush port screw back into place. Presumably, bay water was drawn into the hole. (I don't know if that hole then feeds into the impeller or by-passes it.) In any event, any water that might have been drawn in would not have passed through the screens below the impeller. Is it possible that something was drawn in and is now obstructing a feeder hole in the head's water gallery? Perhaps when I back flush, the obstruction is temporarily removed, and then sucked back into place when I run the engine?
 
Possible that there is a loose bit o junk in there. At this point, it being clear that the puffing is exhaust, I would drop the LU, and back flush well. Then connect the water hose to the water pipe, and once getting a good flow out of the pee tube consistently, you know that the cooling system is clear.
 
More to the mystery. I back flushed again as you suggested (and removed thermostat). Before reattaching the lower unit, I attached a hose to the water pipe. Water came almost exclusively out of the side exhaust. But when that hole was plugged, much water came out of pee hole and down the channel that would go through the prop if the lower unit had been connected. Take finger off side exhaust and again water gushes out of the side and nothing out of the pee hole or the prop exhaust. Puzzled as to how the motor determines which way to direct the flow. The side exhaust water doesn't seem to get hot, whereas the water directed toward the lower unit was getting hot. I guess I'll try to back flush with a stronger flow and see if that helps.
 
Sorry for the mistaken reference. The hole I'm referring to is shown in the photo I posted in #5. As I indicated earlier, I wasn't sure what it was called. It doesn't seem to have a label in any of the illustrations. You have since referred to it as the "side drain."
 
Back
Top