Experience re: overheat and impeller failure

[2014DF25ARS]

I thought I would share my current experience with overheating on my DF25A motor. I suppose there will be nothing new in this story for many of you, but I don't have much experience with outboard engines, and maybe the story & photos will be useful for some others as well.

My motor is about 2 years old now, with 104 hrs on it. I have an SMIS display, so I am able to see engine messages and operating temp, etc.

My motor has worked without problems since new, until an outing about two weeks ago (hit 100 engine hrs on that trip). After a 45-min cruise at around 5000 RPM, I was locking through a dam, and as I was idling waiting to enter the lock, my overheat alarm went off. I turned off the engine and then couldn't get it to start again. I waited a minute or two (drifting away from the dam!) and tried to start it again, and it started. As I idled into the lock in gear, it overheated again. Once through the lock, I started the motor again and cruised at 4500-5000 RPM for another 35-40 mins to my destination without further problem.

Now after a couple more outings, I see on the SMIS display that my engine is running at a constant 145-150 F deg temp until the RPM drops below about 1150 RPM, at which point the engine temp starts climbing until the engine overheats. If I use the "fast idle" lever to bump the RPM from 900 (idle) to 1200, then the temp quickly drops back to 150 F.

My motor is peeing normally at all RPM. I can't see any difference in the telltale at idle (900 RPM) vs 5000 RPM.

The Maintenance Schedule in the Service Manual says at 100 hrs I should inspect the thermostat. And it says I should inspect the impeller every 200 hrs or 12 months (whichever comes first). (Of course I have never inspected my impeller before, because I haven't had any problem with it.)

Last night I dropped the foot and pulled out the impeller. I will share some photos of what I see. I see that the tip is broken off one of the impeller blades, and as a result that blade doesn't contact the impeller sleeve when the blade is on the input side of the housing. You see that the housing/sleeve is eccentric, with the output opening at the "tight" side of the circle.

I can see that the broken blade reduces the efficiency of the impeller, but my guess is that this is not the root of my cooling problem. I have to wonder where the tip of that broken blade ended up! Hopefully I'll find time this evening to open the thermostat housing, and I really hope to find the blade tip there...

One lesson learned: just cause your motor's peeing, doesn't mean it's cooling!

[Solarman]

Might put a large stocking over leg, or a screen over water tube, when you get thermostat open, and flush water at a goodly rate backwards, this might dislodge any pieces and get caught in screen/ stocking. Just a thought for some piece of mind.

Those pics tell me those pieces are not real big? They may have blown through? A Fragmenting impeller usually indicates motor was, at some time, turned over when impeller was dry? It is only water lubricated.

Good luck. Post back what happens when able.

[Moonlighter]

I thought I would share my current experience with overheating on my DF25A motor. I suppose there will be nothing new in this story for many of you, but I don't have much experience with outboard engines, and maybe the story & photos will be useful for some others as well.

My motor is about 2 years old now, with 104 hrs on it. I have an SMIS display, so I am able to see engine messages and operating temp, etc.

My motor has worked without problems since new, until an outing about two weeks ago (hit 100 engine hrs on that trip). After a 45-min cruise at around 5000 RPM, I was locking through a dam, and as I was idling waiting to enter the lock, my overheat alarm went off. I turned off the engine and then couldn't get it to start again. I waited a minute or two (drifting away from the dam!) and tried to start it again, and it started. As I idled into the lock in gear, it overheated again. Once through the lock, I started the motor again and cruised at 4500-5000 RPM for another 35-40 mins to my destination without further problem.

Now after a couple more outings, I see on the SMIS display that my engine is running at a constant 145-150 F deg temp until the RPM drops below about 1150 RPM, at which point the engine temp starts climbing until the engine overheats. If I use the "fast idle" lever to bump the RPM from 900 (idle) to 1200, then the temp quickly drops back to 150 F.

My motor is peeing normally at all RPM. I can't see any difference in the telltale at idle (900 RPM) vs 5000 RPM.

The Maintenance Schedule in the Service Manual says at 100 hrs I should inspect the thermostat. And it says I should inspect the impeller every 200 hrs or 12 months (whichever comes first). (Of course I have never inspected my impeller before, because I haven't had any problem with it.)

Last night I dropped the foot and pulled out the impeller. I will share some photos of what I see. I see that the tip is broken off one of the impeller blades, and as a result that blade doesn't contact the impeller sleeve when the blade is on the input side of the housing. You see that the housing/sleeve is eccentric, with the output opening at the "tight" side of the circle.

I can see that the broken blade reduces the efficiency of the impeller, but my guess is that this is not the root of my cooling problem. I have to wonder where the tip of that broken blade ended up! Hopefully I'll find time this evening to open the thermostat housing, and I really hope to find the blade tip there...

One lesson learned: just cause your motor's peeing, doesn't mean it's cooling!

As to the root cause of your overheating problem: most certainly, that damaged impeller is it!

Age (and lack of frequent use) makes them lose flexibility and bits then start to break off.

I used to work with a guy that bought a new boat with a 60hp Yamaha on it. But then he never used it. After 18 months he finally got round to starting it up - no water flow! Impeller rotten. Continued on like that for about 6 years, replacing that impeller every couple of years after no use! Sold the boat with only about 20 hours on it.

Whether you have a residual problem due to bits of it in the water passages somewhere - probably not. Most likley theyve been flushed out, but try what Solarman said.

I hope you did a full water pump kit including the ss housing when you replaced it? Again, it might look OK to the naked eye, but any small deviation in shape will affect its efficiency. We always replace them when we do a pump service.

The other good reason to check them annually is that it makes you drop the leg, change the gear oil, grease the splines on the drive shaft and prop and grease the bolts holding the leg on. All of which is a very good idea and prevents or at least reduces the likelihood of trouble getting the leg off at a later time.

[2014DF25ARS]

I'm reporting back with results on my overheat issue. I replaced the impeller using the parts in my "Suzuki Maintenance Kit". This means I replaced the rubber impeller, the stainless housing cup, and the stainless base plate. I did NOT replace the gasket below the base plate (though one was included in the kit), because the original gasket looked good and I couldn't get it off without tearing it up, which would then mean scraping it off. I figured I'm better off leaving the original there.

Before installing the foot, I did remove the thermostat to look for the broken/missing impeller tip. I didn't see anything in the thermostat housing, so I did rig up a garden hose with a tube that fit tightly into the thermostat housing, and I back-flushed both sides of the thermostat channel - the input side and the output side, letting the water drop from the motor leg into a bucket. I did not find any signs of the missing impeller pieces, so I'm hoping they did flush through my motor as they wore off. Hopefully the tip wore off gradually rather than in one piece, because I can't imagine the whole impeller tip making it through the opening in the thermostat.

Y'all nailed it re: the results. I finally got my boat in the water yesterday, and it cools fine at idle now. Runs at about 145 deg across the full RPM range. Regarding the cause of the failure in my 100-hr motor, I must admit that when I first put the motor on my little boat, I started it in a bucket of water on the trailer in my driveway. I filled the bucket to about an inch above the water inlet and started the motor. It wasn't peeing, so I shut it off and filled my bucket to the top - about another inch. So the water level was probably about level with the ventilation plate on the foot. I started the motor again, and it still wasn't peeing. I thought perhaps it wouldn't pee until the thermostat opened, so I let it idle for about 30 seconds. It didn't start peeing, so I shut if off again. If I recall correctly, I think my next move was to connect a garden hose to the flush port and start it again, and it still didn't pee. So finally I fit a trash bin under the motor - much taller than my original bucket - and when I started the motor it began peeing. Bottom line is that I probably ran it on and off for as much as a minute or two at idle with the impeller dry. After replacing the impeller recently, I now see that the water level must be at/above the impeller to "prime" the impeller, and the impeller sits on a plate which is essentially level with the break point between the foot of the motor and the mid-section - well above the water inlet grate on the motor.

So to summarize:

The damaged impeller blade was causing my motor not to cool at idle, though it cooled fine at higher RPM.
The early failure of the impeller may have been caused by my 1-2 mins of dry idle when the motor was new.
It appears that the broken bits of my impeller flushed through the system.

Thanks to Solarman and Moonlighter for sharing your experience on this forum!