Over temp alarm at idle speed.

[Mike S.]

I have a 2000 Vmax ox66 225 on my Skeeter. I keep getting the over temp alarm when I'm idling. It started early this year, and I found a leaking head gasket, 2 high I repaired. Then it happened again. I changed the impeller and housing. Still happening. So I changed both thermostats and cleaned the pressure relief valve in the bottom of the motor. I have chased down wires for bad connections, and wearing.

It has been smoking real bad at start up, idling rough, and running rough through the power band. I read that was a sign of a bad oxygen sensor. So, I changed that yesterday, and haven't gotten to run it yet. Any help would be appreciated.

[Slipkey]

Usually, that happens when a piece of grit gets lodged in one of the thermostats, but since you've replaced those recently...  Your telltale stream is flowing OK?  If it's slower than it should be at idle, you might have some calicification/build-up and can try descaling. 

For the rough running, if the sensor wasn't the issue, have you replaced your plugs, checked the integrity of wires from the distributor and double-checked the correct firing order?

[Waterfoul]

Mercury!!!  Once you go black...   

Give Ted at TLC Marine repair in Marne a call.  Tell him you're a friend of mine.  He has never missed on any issue I've ever had or any issue my friends have had.

[Mike S.]

I don't know about the over temp issue, but that oxygen sensor made a HUGE difference. The boat went into the 70's again. That makes me happy. The power rolled on smooth, and it felt like it did the year I bought it. I stopped in to Baker Marine this afternoon. Hes going to let me bring it to him one afternoon next week to run it in his tank and use his infrared thermometer to check temps while its running.

[21XDC]

Do you have the "New Style" Mushroom shaped poppet valve?  I suggest you change yours if you have the original. They are cheap and easy to change.

[Mike S.]

Well, the oxygen sensor was short lived. When I launched the boat the night after my good ride, it ran just like it did before I changed the o2 sensor. It ran rough, smoked like crazy, and would only go 64 at best. The sensor I bought was from ebay, in original packaging, but at half price. I'm assuming I may have just gotten a bum sensor. I found on many forums where guys have run the NGK universal sensor, NTK 21006, and had great results. The 4 wires are the same color codes, but you have to splice the Yamaha plugs to it. No big deal there. This sensor costs $60 at a parts store. I put one in last night, and will hopefully get to run the boat today or tomorrow.

As for the mushroom style poppet valve, I didn't know there was one.

[32eml24]

I dont know much about your specific outboard but if this thread were about a car i would first ask if the rough running and over temp alarm started at the same time. If yes, it would be worth investigating the temp sensor. A bad temp sensor fits the bill for both symptoms but until you diagnose it properly you are just throwing parts at it and hoping...

[Mike S.]

Next step, mechanic. Once it has a clean bill of health, for sale. My wife gave me the go ahead on a new one as soon as I can sell mine.

[YpsiBass]

Congrats on the go ahead. Going to get another skeeter? Interested in a Stratos..?

[Waterfoul]

If you are going to get a "newer" boat I'd probably go with something that doesn't FLY at 65 mph!  LOL!!!

[21XDC]

Just trying to help... Please read links fully...

http://www.bbcboards.net/yamaha-motors/409191-over-heat-alarm-buzzer-sounding.html

http://www.bbcboards.net/yamaha-motors/414256-thermo-switch-assy.html#post4020656