Yamaha 115 2 stroke overheat buzzer.

[Malcolm W]

Just thought I would share my experience in case this happens to one of you guys. The motor is a 2003 115 CV premix. It has approx 1500+hours and always well flushed.


3 weeks ago I took the boat out and as I increased revs the overheat buzzer came on. The motor also cut revs. I shut the motor down, re-started and the alarm went away. Picked up revs again and the same thing happened? The heads appeared cool to the touch? So home we go to sort this out.

1. First thing was a full service including the water pump. Back in the water and off goes the buzzer again. The motor appears cool.

2. Back home and replaced the thermostats, still no luck. Took the thermostats out for a short run and the heads ran stone cold to the touch.

3. Borrowed an IR heat gun, took out the warning switches, put them in a pot and slowly heated them to 85°C. Off goes the buzzer on both as per the manual at 85°C. Did a compression test and all 4 pots came in at 128 to 130 PSI.

4. Took the boat out again with the motor cover off and using the IR gun found the starboard side was getting hot, but would cooldown within 2-3 seconds of dropping revs off. The conclusion was a partial restriction of the cooling galleries.

So off came both head covers + the heads and sure enough both had a build up of calcified scale and a rubbery silicone substance. Even though some of it looks like salt, I couldn’t find any with the taste test.

Reading other forums I had found some guys use vinegar to try and dissolve this scale. I put the heads in vinegar and found after 20-30 minutes approx 60-70% of the scale had dissolved (but not the rubbery product).

I scraped and cleaned everything up, put new gaskets on and she’s like new again. The vinegar didn’t appear to cause any problems with the alloy in that time, so from now on(once a year) I’m going to tilt the motor up, take the thermostats out, tip neat vinegar in for 30 mins and then flush.

Sorry it’s a bit long,

Mal.

[WalrusLike]

I've got a 2011 115 2 stroke so I was very glad to read your experience, thanks for sharing especially with such good detail.

If you ever find out what it was, please update this thread... I am sure a few of us would be very interested.

Does anybody know a way of telling if the thermostat has opened when you are flushing it with muffs after its gotten cold? I think Spaniard King said I could tell by taking the cover off and touching the heads?

Is there any way to do it without taking the cover off? Sometimes it's dark and I am buggered and I don't want the cover off because I am never sure I got it back on again properly.

[Malcolm W]

Does anybody know a way of telling if the thermostat has opened when you are flushing it with muffs after its gotten cold? I think Spaniard King said I could tell by taking the cover off and touching the heads?

Is there any way to do it without taking the cover off? Sometimes it's dark and I am buggered and I don't want the cover off because I am never sure I got it back on again properly.

After playing around with the temp gun the thermostats open at 50 deg (thats also marked on the thermostats) and it only takes about a minute or so from cold for the head to reach that temp. Intrestingly there is a reasonable amount of water bypassing the thermostats through 2 holes either side of the themostat.
If you have come back from a trip with no overheat problems you can safely say the themostsats will open after a short time on the muffs

[WalrusLike]

Good to know.... Many thanks.

Wonder what the silicon and the scale deposit were....