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  1. #1
    Join Date
    Aug 2018
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    Green Bay, WI
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    Default Water pump fail - Did I kill the motor?

    Just got back the lower unit foot of my 1974 Mercury 50hp from the shop. They replaced the drive and shift shaft seals and the water pump impeller.
    So I reattached the foot, no problems with shifting. Put cups the water intake and fired it up in the driveway. No problems, water was coming from the tell tale port but was rather weak flow, but his motor has always had a weak flow out that port.

    So, dropped it in the river (bad idea) and drive upstream and then down stream. Was watching for cooling water and it looked ok. Ran it to top speed for about 10 min, then idled about 4 miles down stream to the dam. Just as I started heading back upstream, the motor started running rough and I shut it down. I noticed steam coming out of the tell tale port.

    I let it sit for about 30 min, then removed the cowling cover. It was HOT! Let is sit about 20 more min and then started splashing some water on the engine to cool it down further.

    I then tried to start it again and it would run upstream at only 1500 rpm, anything more seems like it was pushing it.
    About 2 tenths of a mile later, it started running rough again and no water, just steam coming out of the tell tale.

    So, with no other choice, AI repeated the 45 min cool down and short slow speed hops just to get me closer to civilization.

    Luckily I ran into a guy who towed me 3 miles back to the boat landing.

    My question is: what kind of damage could I have done to the motor and how likely is it to be permanent?

    Once cool it sounds ok, but after getting too hot it was getting rough and just just itself down. Does it have any built in protection?

    I'll be tearing it apart tomorrow to check the cooling system. Is there a way to check for impeller parts inside the motor without pulling the power head?

    Thanks for any advice...

  2. #2

    Default Re: Water pump fail - Did I kill the motor?

    Do a compression test.

  3. #3
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    Default Re: Water pump fail - Did I kill the motor?

    Pull the gearbox and adapt the garden hose to the water tube then run the motor and see if you get good flow out of the telltale and the engine does not overheat. If you still have poor flow out the pisser you ihave no choice but to pull the powerhead and see where its stuffed up. I doubt you damaged the engine but if you pull the powerhead it wouldnt hurt to put in new crank seals.
    Last edited by kimcrwbr1; 08-15-2018 at 02:04 AM.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  4. #4
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    Default Re: Water pump fail - Did I kill the motor?

    Ok, so I dropped the foot and immediately knew the problem. The brand new impeller that the dealer shop installed is totally gone. It didn't last an hour on the water.
    What would have caused that? It worked for the first hour, then failed down stream, naturally down stream.

    I took the entire foot to them to replace the drive and shift shaft seals, they replaced the water pump impeller because it was opened up, so that was recommended, but to fail within 1 hour? Now the whole motor is wrecked. Shop is Sportomotive, Appleton, Wi - avoid them.

    So my next question, on a 74 mercury 50hp, where would one start looking for the impeller pieces?
    Last edited by 74merc50; 08-15-2018 at 09:51 AM.

  5. #5

    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by 74merc50 View Post
    Ok, so I dropped the foot and immediately knew the problem. The brand new impeller that the dealer shop installed is totally gone. It didn't last an hour on the water.
    What would have caused that? It worked for the first hour, then failed down stream, naturally down stream.

    I took the entire foot to them to replace the drive and shift shaft seals, they replaced the water pump impeller because it was opened up, so that was recommended, but to fail within 1 hour? Now the whole motor is wrecked. Shop is Sportomotive, Appleton, Wi - avoid them.

    So my next question, on a 74 mercury 50hp, where would one start looking for the impeller pieces?
    Right here I think would be a good start. How about a Mercury dealer? At least you don't have my problem - two 1952 motors and a 1960.

    Bill

  6. #6
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by Ram Jet View Post
    Right here I think would be a good start. How about a Mercury dealer? At least you don't have my problem - two 1952 motors and a 1960.

    Bill
    I meant where in the engine to look, but after thinking about this, it's more likely that the pieces disintegrated in place and into small enough bits to pass through the engine. The impeller was destroyed. The cup was vulcanized and severely scored. It stopped pumping pretty quickly. Remember this was the first hour of operation for this impeller. See pics.

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  7. #7

    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by 74merc50 View Post
    I meant where in the engine to look, but after thinking about this, it's more likely that the pieces disintegrated in place and into small enough bits to pass through the engine. The impeller was destroyed. The cup was vulcanized and severely scored. It stopped pumping pretty quickly. Remember this was the first hour of operation for this impeller. See pics.

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    I have never seen a water pump impeller so totally destroyed but then I'm not a professional outboard mechanic.. My first thought was that the mechanic left a nut, bolt or washer in the impeller housing. Then you pointed out that the rubber had vulcanized to the impeller housing. It's likely that there was insufficient water flow through the muffs when you initially ran the engine. When I replace an impeller I lightly coat the inside of the water pump housing and the impeller blades with lithium grease to prevent a "dry start-up". Your two year old impeller looks good enough to reinstall.

    Bill

  8. #8
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by Ram Jet View Post
    It's likely that there was insufficient water flow through the muffs when you initially ran the engine. When I replace an impeller I lightly coat the inside of the water pump housing and the impeller blades with lithium grease to prevent a "dry start-up". Your two year old impeller looks good enough to reinstall.

    Bill
    It's more unlikely since the tell tale had water flowing out of it.
    Then it ran for over an hour on the river.
    I use Mercury Marine Grease on all repairs.

    The shop job had the drive shaft so tight it's not funny. Had to put a vice grips on the drive shift to rotate it. The fact that the shop dink had to turn it backwards does not help.

    Either way, tomorrow it's gets the test. Hoping for the best.

  9. #9

    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by 74merc50 View Post
    It's more unlikely since the tell tale had water flowing out of it.
    Then it ran for over an hour on the river.
    I use Mercury Marine Grease on all repairs.

    The shop job had the drive shaft so tight it's not funny. Had to put a vice grips on the drive shift to rotate it. The fact that the shop dink had to turn it backwards does not help.

    Either way, tomorrow it's gets the test. Hoping for the best.
    I think you're better off doing your own repairs. No one touches my outboards or motorcycles although there's some things I can't do on cars anymore.

    Good luck. "Nothin's so bad that it couldn't be worse".

    Bill

  10. #10
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    Default Re: Water pump fail - Did I kill the motor?

    Until you replace the impeller housing and plate dont waste money on another impeller. To properly test the cooling system allways use a barrel of water at least five inches above the cavitation plate. Put dish spap on the impeller and spin the driveshaft clockwise as you put it together. Especially on a merc if you spin the driveshaft counterclockwise after installing the impeller you must take it apart and do it correct.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  11. #11

    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by kimcrwbr1 View Post
    Until you replace the impeller housing and plate dont waste money on another impeller. To properly test the cooling system allways use a barrel of water at least five inches above the cavitation plate. Put dish spap on the impeller and spin the driveshaft clockwise as you put it together. Especially on a merc if you spin the driveshaft counterclockwise after installing the impeller you must take it apart and do it correct.
    Never thought of dish soap. More environmentally friendly. Thanks.

    Bill

  12. #12
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    Default Re: Water pump fail - Did I kill the motor?

    The power head has to be chock full of broken impeller pieces that could block water passages and cause local, destructive overheating.

    You could take a chance and just run it, but I'd pull the left side and back covers off to clean the works out. Alternatively, with the LU off, you might try back flushing it by shooting compressed air and water mix into the tell tale connection.

    Jeff

  13. #13
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by kimcrwbr1 View Post
    Until you replace the impeller housing and plate dont waste money on another impeller. To properly test the cooling system allways use a barrel of water at least five inches above the cavitation plate. Put dish spap on the impeller and spin the driveshaft clockwise as you put it together. Especially on a merc if you spin the driveshaft counterclockwise after installing the impeller you must take it apart and do it correct.
    LOL - Of course I replaced the housing! There is no way I would even try to to reuse that train wreck.
    Parts replaced:
    1 Impeller # 47-89983T
    1 Pump Housing # 46-77822A1 includes metal cup.

    So, I am a bit confused on your comment about turning CCW because I just got a call from the shop owner who adamantly stated that you can do no harm by turning the drive shaft CCW. This is disputed by what one of his own techs said. I believe he is simply trying to cover his A$$ with a lie.

    He claims that once you turn it CW, all the fins straighten out, maybe so, but probably crack or weaken midway.

    On reinstalling (one man job) I had to pop it into forward and rotate the prop just a tiny amount to align the drive shaft splines. I suppose turning the top crank would be better. Once aligned, I snap it back to neutral and close up. I suppose this is bad...now I want to crack it open to see if the fins flipped during the 5 degree or less rotation. I used ample soap and a bit of marine grease on each fin during assembly so it is very slippery in there. Think I'm probably ok, since this is how I've always done it.

  14. #14
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by fastjeff View Post
    The power head has to be chock full of broken impeller pieces that could block water passages and cause local, destructive overheating.

    You could take a chance and just run it, but I'd pull the left side and back covers off to clean the works out. Alternatively, with the LU off, you might try back flushing it by shooting compressed air and water mix into the tell tale connection.

    Jeff
    Man I hate to crack this motor open, it's like open heart surgery. The case is painted or powder coated at all the seems. They really sealed them tight back in 74. It is my understanding that of it makes it up the uptake tube, it will likely just pass through the system as the exhaust port is nearly as wide as a 2x4. Also, isn't the tell tale tap point (say that 5 times fast) at the top of the motor? It's just indicating that the cooling system is FULL.

  15. #15
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    Default Re: Water pump fail - Did I kill the motor?

    I would say that impeller in post # 6 ran dry for some reason to be determined.-----Someone is not owning up to a mistake.

  16. #16
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    Default Re: Water pump fail - Did I kill the motor?

    The good news is that the old boy who is now 91 says that this has happened to him before and that he limped it home when it was over heating. Check me if I'm wrong, but even in 1974 they had temperature protection on motors that would prevent them from running above 1500 rpm if HOT and shut it down completely if it was HOT HOT!!!
    That's how it was behaving the day the pump failed. It would make sense to me. There is a sensor on the left engine cover that I'm guessing is a temperature sensor.
    It's analog and just controls the carb or thunderbolt ignition. The shop clerk insisted that older motors have no protection whatsoever and only started with EFI motors.

  17. #17
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    Default Re: Water pump fail - Did I kill the motor?

    I would say that impeller in post # 6 ran dry for some reason to be determined.-----Someone is not owning up to a mistake.
    Yes, it looks like it was dry, however, the motor ran fine on the cuffs, with water coming out of the tell tale. It ran fine on the water for about 1 hour, but honesty the TT flow looked weak.. then it failed fully. My question is how does a fully submerged lower unit on a boat with no PTT get bone dry? Even with weeds or a plastic bag (as the shop owner insists it was) enough water would still be leaking in to prevent a bone dry condition. I believe it was extreme friction, even in water. Once the parts got all twisted up, it was pure friction chaos. Boat is never run dry, ever. I've seen people run their motor on the trailer and back in with the trim up. By the time they park and get the trim down, it could be several minutes totally dry. I'm sure they buy a lot of impellers.

  18. #18
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    Default Re: Water pump fail - Did I kill the motor?

    Just as an update, I just connected the cuff and started the motor. One crank and she fired right up. Took about 15 to 20 seconds to see water out the tell tale, but it was flowing. Not super strong on idle, but when I reved it to 3k, it was shooting out pretty strong. Motors sounds perfectly fine and strong too. These old girls are built like a tank...that's why I keep her on the water. Now back to the river for sea trials, but not so far downstream this time.

    Lesson learn from all this? Double check all dealer shop work and do what you can yourself.
    Last edited by 74merc50; 08-16-2018 at 12:14 PM.

  19. #19
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    Default Re: Water pump fail - Did I kill the motor?

    Just a few pictures of the 44 year old boat ready for the water. Wish me luck.
    I will add my testimonial that Mercury sure made a tough / long lasting motor.
    No plastic junk parts that break at perfectly calculated intervals...like newer models...and cars.

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    Last edited by 74merc50; 08-16-2018 at 12:40 PM.

  20. #20
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    Default Re: Water pump fail - Did I kill the motor?

    There is no warning horn or overheat protection on that motor !!!

  21. #21

    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by 74merc50 View Post
    LOL - Of course I replaced the housing! There is no way I would even try to to reuse that train wreck.
    Parts replaced:
    1 Impeller # 47-89983T
    1 Pump Housing # 46-77822A1 includes metal cup.

    So, I am a bit confused on your comment about turning CCW because I just got a call from the shop owner who adamantly stated that you can do no harm by turning the drive shaft CCW. This is disputed by what one of his own techs said. I believe he is simply trying to cover his A$$ with a lie.

    He claims that once you turn it CW, all the fins straighten out, maybe so, but probably crack or weaken midway.

    On reinstalling (one man job) I had to pop it into forward and rotate the prop just a tiny amount to align the drive shaft splines. I suppose turning the top crank would be better. Once aligned, I snap it back to neutral and close up. I suppose this is bad...now I want to crack it open to see if the fins flipped during the 5 degree or less rotation. I used ample soap and a bit of marine grease on each fin during assembly so it is very slippery in there. Think I'm probably ok, since this is how I've always done it.
    Since you lubed it really well I doubt you'll have a problem.

    Bill

  22. #22
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by racerone View Post
    There is no warning horn or overheat protection on that motor !!!
    Yes, I realize that, but it does protect itself, apparently....

    When it gets hot, I'm guessing above 135 or 150, for whatever reason, the motor will revert to "crawl" mode and not allow you to exceed 1500 rpm.
    If the temperature increases beyond 220 it will sputter and quit. It's not a digital system, it's analog and as I pondered earlier, likely tied to the carb. Wonder if some mechanic out there could explain this operation further, maybe it's just a symptom of over heating the carb itself and it vapor locks.
    Either way, it seems to have protected the engine from severe damage...thankfully.

    As a former industrial controls engineer myself, I can't imagine anyone designing any kind of boat motor which has the Achilles heel of a rubber impeller to cool the engine without designing in some type of thermal safeguard. The only difference is today it's all done digitally. Back then it was done using analog circuitry.

  23. #23
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    Default Re: Water pump fail - Did I kill the motor?

    There is no warning horn / no shut down system of any kind on that motor !!!!----Can you not accept that concept ?----After all that motor was basically designed / built by a stubborn German engineer in the 1950's and sold to the public that perhaps knew more about motors than folks today..

  24. #24

    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by 74merc50 View Post
    Yes, I realize that, but it does protect itself, apparently....

    When it gets hot, I'm guessing above 135 or 150, for whatever reason, the motor will revert to "crawl" mode and not allow you to exceed 1500 rpm.
    If the temperature increases beyond 220 it will sputter and quit. It's not a digital system, it's analog and as I pondered earlier, likely tied to the carb. Wonder if some mechanic out there could explain this operation further, maybe it's just a symptom of over heating the carb itself and it vapor locks.
    Either way, it seems to have protected the engine from severe damage...thankfully.

    As a former industrial controls engineer myself, I can't imagine anyone designing any kind of boat motor which has the Achilles heel of a rubber impeller to cool the engine without designing in some type of thermal safeguard. The only difference is today it's all done digitally. Back then it was done using analog circuitry.
    I agree but impellers are very durable. According to an OMC repair manual I have the impeller blades actually leave contact with the impeller housing at high speeds. That's why I installed a tell tale (pee hole) on my 1960 Johnson 3 H.P. and will do so on my 1952 Merc Super 10 - as soon as I can figure out a place to put it.

    Bill

    Bill

  25. #25
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by racerone View Post
    There is no warning horn / no shut down system of any kind on that motor !!!!----Can you not accept that concept ?----After all that motor was basically designed / built by a stubborn German engineer in the 1950's and sold to the public that perhaps knew more about motors than folks today..
    Jawohl! I KNOW it doesn't have a warning horn. I'm just relating the actual operation I observed. However it happened, by design or by pure f'n magic, the motor would absolutely not go above 1500 rpm when hot and totally die when very hot. Today when totally cool, it will rev to 5k with no hesitation and sounds fine. Either way, that stubborn German engineer must be pretty smart.

  26. #26
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    Default Re: Water pump fail - Did I kill the motor?

    Motor was seizing up or running with other issues.-----There is no warning system / horn / shutdown system of any kind on that motor !!

  27. #27
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    Default Re: Water pump fail - Did I kill the motor?

    You mention weak flow from the tell-tale , this could have been from a leaking pump assembly and running it wide open on plane could have put the water pump base above the water level and you were sucking air into the pump. You pump is above the cavitation plate so its slightly out of the water and only the lower unit pickup holes are supplying water to the pump.
    Also you hot exaust gas passes thru there too
    Last edited by Bt Doctur; 08-17-2018 at 12:59 PM.

  28. #28
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    Default Re: Water pump fail - Did I kill the motor?


  29. #29
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    Default Re: Water pump fail - Did I kill the motor?

    Quote Originally Posted by Bt Doctur View Post
    You mention weak flow from the tell-tale , this could have been from a leaking pump assembly and running it wide open on plane could have put the water pump base above the water level and you were sucking air into the pump. You pump is above the cavitation plate so its slightly out of the water and only the lower unit pickup holes are supplying water to the pump
    Pump and gaskets were tight. The intake below the pump is large and under pressure, so can't see a condition where it could actually "suck air".
    If anything, at high speed, water is being forcibly rammed into the pump at high pressure which should make the pump work even better.

    The weak stream was at idle only. I've seen motors at idle that pee like a racehorse and some like and old man. This motor has always had BPH.
    No wonder, it's 44 years old. That probably over a hundred in boat years.

  30. #30
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    Default Re: Water pump fail - Did I kill the motor?

    74Merc50, Is your anti-Ventilation plate level with lowest point of the bottom of hull?

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