99 90hp 2 stroke over heat alarm

[amoler821]

i have a 99 90hp 2 stroke 3cyl. the oil injection is disconnected and i mix oil when i fuel up. The lower unit is new. I had it gone over and compression tested last year and it got a clean bill of health.
i have had it out a few times breaking in the lower unit per the mfg instructions and had not gone over 3000 rpm until the last trip out. over 3000 rpm i get the overheat alarm. i back off the throttle and its fine. i can idle around and even get up to around 1100 rpms all day long without issue. only when i get up in rpms do i get the alarm. ive done some digging thru the forums and thought it might be the poppet valve. when i called the dealer he said all they ever replace is the diaphram so he ordered me that and the gasket. when i took off the poppet/thermostat cover the spring had pressure on the cover, the diaphram is not torn or deteriorated the passages look clear, i heated the thermostat to check operation and it opened and closed. Would i have seen something obviously wrong with the poppet valve?
so my question is...what else could it be? i haven't put it back together yet (waiting on the thermostat to come in) but i was hoping someone could give me other things to look at while im waiting. There's water coming out the tell tale at idle, and it increases as rpms increase. the lower unit came with the water pump installed, so thats new.

 

[flyingscott]

Check the water pump impeller.

 

[amoler821]

With a new water pump installed on the lower unit when i got it is it worth pulling again? And if its pumping water from the tell tale is it possible there is still a problem with the impeller?

 

[racerone]

Is this SEI aftermarket stuff ?

 

[amoler821]

Yes it is.

 

[racerone]

Inspect the low budget pump I would say.

 

[wn6ngp]

I think I have the very same motor. Mine is a model year 2000 90hp made in '99. It seems like if the tell tale is squirting full strength you wouldn't have a pump problem but is suspicious that it is happening just after you changed the lower unit.

On my motor there is a plug on the water jacket. I removed that and put a barbed hose fitting for a water pressure gauge. I just used the speedometer gauge as a pressure gauge, you might try that. On my motor I see the pressure go way up with rpm and then cuts back quickly, I assume thats the pop off valve operating.

I recently replaced the thermostat as it was sticking open a bit keeping it from warming up. Its easy to pull off the thermostat and check. Yours may not open all the way since you are saying it gets hot at higher speeds. Besides that there are ways you can shade tree mount a temperature probe on the head at least termporarily to see if it is really over heating.

I replaced the oem impeller at about 200 hrs with 20% salt usage. I was surprised to find the impeller was like in new condition. I replaced it with the cheap one and its been fine. My huge problem then was that the the lower unit was stuck on but that's whole another story.

 

[amoler821]

Racerone : was SEI lower unit not the way to go?

WN6NGP: where u tired in the barb fitting for the pressure gauge, could it also be used to maybe "t" in a pressue and manual temp gauge? Im away for the week so im not able to look over the engine

 

[wn6ngp]

Racerone : was SEI lower unit not the way to go?

WN6NGP: where u tired in the barb fitting for the pressure gauge, could it also be used to maybe "t" in a pressue and manual temp gauge? Im away for the week so im not able to look over the engine

I don't think that's a good place to tap in a manual temp gauge since you could have plenty of water pressure, including the tell tale, yet have overheating if your thermostat was stuck or if you had a restriction elsewhere.

On my motor the oem switch temperature sensor is mounted in a cavity adjacent to the spark plug on the port side of it. To add my manual one I took a car sending unit filed it down to an interference fit, covered it with thermal grease and then pushed it into the cavity on the other side of spark plug (the starboard side).

Are you sure its overheating? My oil level and temp sensors are just or'd together so if the alarm goes off it could be high temp or low oil in the tank. some motors have special sequencing of beeps to identify but mine doesn't seem to have that.

 

[amoler821]

No, im not 100 percent sure its overheating. Just going off the alarm. The beep is a single constant beep. I dont think its the oil alarm. I bypassed the oil injection system and mix it myself. The oil tank is there, but it stays empty and the sensor is unhooked

 

[wn6ngp]

No, im not 100 percent sure its overheating. Just going off the alarm. The beep is a single constant beep. I dont think its the oil alarm. I bypassed the oil injection system and mix it myself. The oil tank is there, but it stays empty and the sensor is unhooked

In that case I'd buy or borrow one of those temperature guns, google temperature gun and you will see lots of them for cheap.
The add on temp gauge is nice but in my case I knew it wasn't overheating so I knew what to expect for a reading. Then if it does overheat I'll see that the gauge is different even if its not totally accurate.

 

[flyingscott]

Look at the waterpump impeller. SEI makes a good lower unit but the waterpump impellers are cheaper quality.

 

[amoler821]

Well, i replaced the poppet diaphram and thermostat and took it out today. Still overheating over 3000 rpm. I just pulled the lower unit and water pump and it looks fine. Im going to switch it out with my old water pump from the other lowet unit. I did notice that this one doesnt seem to pump like my old 1 did.

 

[amoler821]

Switching water pumps didnt help. I did notice that the long water tube pulled out and was loose when i pulled the lower unit. It didn't come all the way out but dropped about 8 inches and i had to line it back up when putting the lower unit back on. So it got me thinking...is there a seal at the top of the water tube that could be damaged? Could that explain the weak tell tale stream and is it leaking worse under higher rpm and causeing my over heating issue?

 

[amoler821]

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[amoler821]

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I got my scope cam out and took a look. This pic it the top of the water tube where it goes in the exhuast riser. Looks like the seal broke on half. (Red arrows )

Any idea how to replace that seal?

 

[amoler821]

No Title

 

[amoler821]

Thought i'd post what i found. Turns out the seal at the top of the water pump tube was broken and the water tube was in place, but didnt have the seal around it so the water was escaping. The marina told me the 75-90hp has the same water pump as the larger hp engines and thats probably what saved me. Pulling the powerhead, mid-section and exhaust riser wasnt all that bad on this engine and only took a couple hours. Hopefully when the parts come in it goes back together just as easily.
Thanks everyone for all the replies, tips and help. Hope the post can be useful for others.

 

[amoler821]

Oh...the grainy pic of the water tube shows the broken off piece of the seal laying in the bottom....other pic is of the top where the water tube bolts up and is broken