90hp two stroke overheat alarm

[Tgsx750f2000]

I have a 1999 90hp two stroke that the over heat alarm started going off so I had the water pump changed. It didn't fix it. I take off and within 4 minutes the alarm goes off and I return to idol for about 20 seconds and it stops. I feel the water coming out the pisser and it's not hot at all. Could it be thermostat are maybe bad sensor?

[rougeaut]

Hi I'm sure you have already thought about this but it is not uncommon for the thermostat to be faulty or sticky. My last 2 Strk Yam 2000 had a simular issue if it sat for a while and it would start to overheat then shut it off for ten mins and restart and it was fine. Pull your thermostat out and drop it in boiling water and see if it opens then it should be good, if not replace.
Also take the motor cover off then start it and when the alarm goes off and the water is not scolding hot out of the pisser hose feel the motor area outside the cyclinders as they are water cooled if this is smoking hot then you have issues, blockage or otherwise
if this area is warm or hot you should be able to touch it and not burn yourself then your cooling system is ok.
The other way for a quick check is to pull the thermostat roight out and see if the alarm still goes off.
Cheers

[99yam40]

would be a good idea to test or replace stat and test over-temp switches.
Also have a look at the PRV

Inspect the cooling passages while you open things up, may have to clean them if there is a lot of build up

Tell tail comes from before the motor cooling, it just shows that the water pump is pumping water

Do not run motor without stats in place it needs the back pressure of the restriction to force water through all passages properly

[robert graham]

My motor is also a 1999 Yamaha 90C, and the temp alarm went off just a few weeks ago for the first time since I bought the motor new. I installed a new thermostat and a new pressure control valve(for the first time)...both had a good bit of mineral/corrosion deposits in and around them causing sticking and overheating. On our motors it's a very easy, simple and cheap($50) job. I'll probably not wait 12 years before changing these again! It's a good bet these are the cause of your overheating. Good Luck!

[Tgsx750f2000]

I took out the thermostat and boiled it, it opened fine. I ran the motor without it for a while and without the thermostat cover to flush it. Then installed the cover without the thermostat and ran it down the river, the alarm still went off. So it's not the thermostat. I unplugged the heat sensor and ran it again on the river, ran for almost 40 minutes and no alarm, water coming out the pisser is no where near hot and I can put my hand on the cylinder heads also not hot. So ordered another temp sensor and will see what that does. But I'm going fishing tomorrow with it unplugged, can't waste a vacation sitting at home. Lol

[robert graham]

How did your pressure control valve look?

[Tgsx750f2000]

Don't know where that is so I didn't check it, but that should not have anything to do with alarm since its not really overheating should it?

[Tgsx750f2000]

Unless that was that round plastic thing under the thermostat with the spring on it. It looked fine.

[robert graham]

Yep, X-shaped black plastic thingy with spring on one end and other end against that rubber grommet...maybe it's O.K., but worth checking! Good Luck!

[99yam40]

Don't know where that is so I didn't check it, but that should not have anything to do with alarm since its not really overheating should it?

Well if you are sure it is not overheating and that the overtemp switch is bad you could make sure by testing it.
Running a motor that is telling you it has a problem is never a good thing

[Tgsx750f2000]

Well if you are sure it is not overheating and that the overtemp switch is bad you could make sure by testing it.
Running a motor that is telling you it has a problem is never a good thing

I understand what your saying but I don't have the tools to test it right, the sensor works but it must be going off just to soon at a lower temp.

[doonda61]

Just tossing in my 2 cents, I have a 2002 90tlra that had the same issue. The guy I bought the boat from had it too high on the jack plate. When the boat was running on plane the water pick ups were right at the surface and the water pump was picking up air as well as water resulting in the alarm sounding after a few minutes of running, slow down to idle speed, alarm quits. So I lowered the engine 2 inches and problem was solved.

[Tgsx750f2000]

Just tossing in my 2 cents, I have a 2002 90tlra that had the same issue. The guy I bought the boat from had it too high on the jack plate. When the boat was running on plane the water pick ups were right at the surface and the water pump was picking up air as well as water resulting in the alarm sounding after a few minutes of running, slow down to idle speed, alarm quits. So I lowered the engine 2 inches and problem was solved.

I don't think it's that because I've had the boat for two years and it just started a couple weeks ago.

[Tgsx750f2000]

Well I changed the temp sensor and still getting alarm.
I'm thinking maybe I need to pull the head cover and check the water passages. Any other ideas?

[Tgsx750f2000]

Update- took it to someone and they checked it out for me. I test drove it today for about a 30 minute run and it seems to be fixed (so happy). He did two things that could have been the problem, he took my thermostat and did something to it so it stays open all the time, he also pulled my lower unit to check water pump and found the bolts holding the water pump housing were loose. Not exactly sure what fixed it but its fixed.