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  1. #1

    Default Yamaha 90 overheating

    I need help. I have a 2003 90 two stroke that overheats on plane. Yesterday I dropped it in the water and idled about 20 minutes through the back channel. Water was pumping great and no problems. Opened up to plane in the bay and immediately overheated, no water from the tell tale. Back down to idle and still no water pumping. Limped 50 yards to the mooring, steaming and buzzer sounding, shut it down. 5 minutes later I started it up and still not pumping water. 15 minutes later, started and pumping weakly. I figured the impeller was cooked so I pulled it apart and no problems, looks great it there; perfect impeller, housing, gaskets, everything. This is a new pump I put in last season, maybe 1 hour on it. Thermostat works fine as well as the pressure valve. Between this and the no power problems I'm ready to dump this POS. The mechanic went all through it last year and couldn't find anything wrong. Any ideas out there before I give up and sell this thing?
    Thanks!

  2. #2

    Default Re: Yamaha 90 overheating

    Were you experiencing high temp alarm before you installed this new pump?

  3. #3

    Default Re: Yamaha 90 overheating

    Thanks for the reply. Yes, it was overheating before the pump replacement. The impeller was deteriorated.

  4. #4

    Default Re: Yamaha 90 overheating

    Since the water pump is working (pissing) at low rpms before you throttle up, it could be that the woodruff key is not properly set into the shaft. At low rpms the key is able to grab the impeller slot, but once you increase rpms the key is slipping out of impeller slot.

    Has the keys shaft slot been messed with in the past? The key itself is replaced with every new pump kit. But if the shaft slot has been gauged in some way that allows the key to sit deeper into the slot this would be a problem. The key should be snug in the shaft slot, but never hammered in so much that a few millimeters aren't raised above shaft.

    Id drop the LU and have a look. We know the impeller works bc the shaft is turning it at low rpms. But not at high rpms.

  5. #5

    Default Re: Yamaha 90 overheating

    I'm glad you mentioned that: I double and triple checked the impeller on the key as I thought that was likely. The key is intact and fitted in the slot in the impeller, with no sign of wear. I visited an outboard mechanic today with the lower end and he verified everything looks great. He's stumped as well. Suggested replacing the thermostat as it hasnt been replaced lately, even though I tested it last year and it seemed to function as normal. I wouldnt think that would affect the tell-tale, but what the Hey, I'll give it a try.
    Thanks again for your replies and ideas.

  6. #6
    Join Date
    Sep 2010
    Location
    ontario
    Posts
    13,648

    Default Re: Yamaha 90 overheating

    Looked for a blown head gasket ???-------Try a compression test.

  7. #7

    Default Re: Yamaha 90 overheating

    Oh geezus....I hope thats not it. Ill pick up a tester and try it though. Thanks

  8. #8

    Default Re: Yamaha 90 overheating

    Hi All,
    thought I'd update as my problem still persists. Ive done extensive diagnosis and it seems the water stops pumping when the motor rises up on plane. I've tried it many times over the last few days and its always the same; no problem at idle right up through fast cruising, but as soon as the boat planes up, the tell tale stops and it overheats. Same thing at in neutral; fine until I lift he motor to a certain height, but with the intake still well under water. I've replaced the water pump with all gaskets and thermostat. Its been checked and double checked by a local well respected mechanic. It seems that on plane, the water pump is above the water level; am I correct that the pump should be sucking the water up at this time? Any reason it wouldn't be? Anyone seen this condition? My family loves being on the boat but theyre getting bored with headway speed all summer. Thanks!

  9. #9

    Default Re: Yamaha 90 overheating

    Quote Originally Posted by Natter View Post
    It seems that on plane, the water pump is above the water level; am I correct that the pump should be sucking the water up at this time? Any reason it wouldn't be? Anyone seen this condition? My family loves being on the boat but theyre getting bored with headway speed all summer. Thanks!
    Yes, the pump "sucks" or turns whenever the crankshaft is turning. And since the impeller is notched to the crankshaft via the woodruff key, it also turns. The crankshaft is turning at all times when the engine is running.

    So if I've read you correctly, when your in neutral with the engine running you've got a steady stream of water exiting the tell tale? And by the way, yamaha 2 strokes have a strong pisser, so to speak. Is this stream strong or weak? And then while still in neutral with engine running, you trim up the engine and the engine stops pissing? Do I have you correct?

  10. #10

    Default Re: Yamaha 90 overheating

    ClassiqAQ, thanks for the reply. Yes, thats it exactly. I raise it in slow increments and and a point, seemingly when the actual pump is higher than the water level, the pee stream dies off. If I lower it immediately, it starts streaming again. The intake is under water the whole time. Same while under way; streaming fine while pushing along at mid throttle, but as soon as the engine planes off, the pisser stops. If I back right off the throttle, stream returns and no overheating. If I dont, she overheats.
    On plane, the water is at the level of the anti ventilation plate, below the pump, right?

  11. #11
    Join Date
    Aug 2017
    Location
    South Africa
    Posts
    89

    Default Re: Yamaha 90 overheating

    Post a pic of your setup, this can help identify the issue a bit easier ....

  12. #12

    Default Re: Yamaha 90 overheating

    Quote Originally Posted by Natter View Post
    ClassiqAQ, thanks for the reply. Yes, thats it exactly. I raise it in slow increments and and a point, seemingly when the actual pump is higher than the water level, the pee stream dies off. If I lower it immediately, it starts streaming again. The intake is under water the whole time. Same while under way; streaming fine while pushing along at mid throttle, but as soon as the engine planes off, the pisser stops. If I back right off the throttle, stream returns and no overheating. If I dont, she overheats.
    On plane, the water is at the level of the anti ventilation plate, below the pump, right?

    Correct. The water pump and housing are the highest mounted component on the lower unit. Because of it's mounted position on lower unit it actually sits in the mid section above the AV plate. Example 1st pic below.

    Click image for larger version. 

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    Pictured below is the water pump kit for your motor, 2003 90TLRB. I've got a red arrow pointing at the base plate. It is possible that when you installed this kit the base plate was installed upside down? The housing would still be able to be screwed down with the 4 bolts because their holes would still line up with the housing bolt holes, so to would the crankshaft hole. But if this plate was upside down, the cut-out water inlet grooves would deflect water instead of allowing water to run through. But at idle when crankshaft is at its lowest rpms, I could see the pump being able to pull in enough water to push through pisser.

    Click image for larger version. 

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    Have you tried running engine at high rpms without trimming up engine? Curious to know if engine is pissing. That would tell us if the issue is being caused by crankshaft rpms or not. Please let us know.

  13. #13

    Default Re: Yamaha 90 overheating

    Thanks for the detailed reply. Yes, I'm very familiar with the water pump and its parts as I've had it apart many times, with success in years past. I'm fairly certain the plate is in correctly as I'm careful to replace the parts as I took them apart, and use an exploded diagram as a guide. Also, I believe the plate will only line up with the cavities below when installed right side up. I've had it checked by an outboard mechanic as well. I haven't replaced the plastic housing as it is in fine shape and that was confirmed by the mechanic.
    The engine is pissing fine at idle and like a firehouse when revved in neutral. No problem either when cruising at mid throttle but not on plane. It seems to me that the pump is losing its prime when its above the water level. Does that make sense?

  14. #14
    Join Date
    Aug 2017
    Location
    South Africa
    Posts
    89

    Default Re: Yamaha 90 overheating

    Is your cav plate in line with the bottom of your keel?

  15. #15

    Default Re: Yamaha 90 overheating

    Yes, I believe it is, more or less. We've run the boat for 14 years and this is a new development. Also, I can get the same result by slowly lifting the motor when in neutral.
    Is there any part or gasket that could be the culprit that would cause the pump to stop drawing water when the water level is below the pump?

  16. #16
    Join Date
    Aug 2017
    Location
    South Africa
    Posts
    89

    Default Re: Yamaha 90 overheating

    It could be that the pipe that pumps the water into the powerhead doesn't seat tightly, you can see it on the pic that ClassicAQ posted, also right next to the impeller cover there is a rubber type gasket between the exhaust area and the pump area ...

  17. #17

    Default Re: Yamaha 90 overheating

    That gasket/grommet thing is new, and I'm fairly certain it fits snugly to the pipe. Again, it's pumping great when the motor is sitting down low in the water. Thanks for the ideas, keep em coming!

  18. #18

    Default Re: Yamaha 90 overheating

    Quote Originally Posted by deejaycee_2000 View Post
    Is your cav plate in line with the bottom of your keel?
    Yes. But the engine height isn't a factor in this case bc the prop will ventilate before the intake loses flow over it. If that's what you were thinking. Before you tear it down again I'd get out and run it as I suggested, high rpms with engine down. The result will narrow down the cause.

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