# Yamaha overheating help



## C-monsters (Mar 28, 2008)

Hope someone can give me advice on this one. I have a 2000 model Yamaha OX66 250 on a 22.5 Edgewater. After getting some fuel intake problems fixed, it has run like a dream out to the edge and back several times. Went out yesterday, and the temperature alarm went on when I was in idle drifting. The alarm went offmaybe 20-30seconds after getting the boat in gear and moving forward. I anchored up and fished for a while, then came in. After getting in the bay, I put it back in idle and let it sit. Sure enough, after about a minute in neutral, the alarm came on again, then went off after getting in gear. The boat is "peeing" normally, and flushed normally back at the dock. Does this ring any bells for anyone out there? Water pump maybe? Thanks for any advice.


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## markw4321 (Oct 4, 2007)

Could be your water pump and or your thermostats. but since you say it is peeing normallyI would first Check and clean your poppit valve.I had a similar problem on a yamaha 150 overheating at idle a few months after i changed out the water pump andI cleaned the poppit and it fixed the problem. links below have discussion and some pictures.first link sounds exactly like your problem onthe same motor. Good luck.

http://www.thehulltruth.com/boating-forum/176259-funky-overheat-ox66.html

http://bbcboards.zeroforum.com/zerothread?id=11060

Mark W


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## sosmarine (Sep 28, 2007)

2000 model. Do you know when the impeller was changed last? If not within 3 yrs it should changed. The poppet valve could be your problem since it is O/H at lower rpm. It may be by passing to much water and at the lower rpm the pump is not pumping as much either. Glad to look at it if you are near Navarre.


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## amarcafina (Aug 24, 2008)

Water pump! when your at idle it's not pushing enough water, when youspeed up it moves more water to cool down some


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## markw4321 (Oct 4, 2007)

Overheat at Idle with a goodstreamthat goes away when up and running would check the poppit valve first.However, in any case, water pump should be changed outasthe motor's maintenace schedule dictates....

Mark W


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## C-monsters (Mar 28, 2008)

Thanks guys. Will look at the poppit and water pump. Not sure when the impeller was changed, if ever. Boat was new to me about one year ago.


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## metal11 (Oct 7, 2007)

The thermostat controls water flow while a motor is below 1500 rpm's and then the poppit valve opens and helps cool at the higher rpm's. Start with a water pump then look at the thermostats then check the poppit valve. If poppit is stuck open motor will not reach operating temp at idle. If it is stuck closed at idel everything works as normal and then will overheat at high rpm's. Just thought I'd pipe in there for you.


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## Daydreamin (Jun 20, 2008)

I had same problem two times. Both times problem was resolved with a new impeller. I asked the mechanic for the impellers both times and they both had visible grooves, shallow and minimal wear on the edges...it was enough to cause temps to rise to warning level at idle.


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## markw4321 (Oct 4, 2007)

The poppit (poppet) valve's function is to keep the engine full of water at low RPM. The valveisspring loadedand is designed to open as thewater pressure in the cooling system increases at higer rpms. The valvecan get clogged with salt scale/deposits and stick open, and that can causecooling water from the pumpto bypass the water jackets and dump out the relief holes that are just below the lower cowling. If thepoppet valveis stuck open all the time, so that it is dumpingwater atidle when you have low water pump pressure you can get an overheat at idle. 

Mark W


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## C-monsters (Mar 28, 2008)

Quick update. 



Using the links sent by MarkW, I cleaned the poppet valve. I let it idle sitting in the water for at least 20-30 minutes, and it did not overheat. There was a lot of debris on the spring, and coating the valve. I guess I will not know for sure until I take it out next, but fingers crossed, so far it looks good. Thanks to all for the replies, and especially to MarkW for the links to detailed instructions how to do this on my engine.



Only three more weeks until snapper season...


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## outbrdwrench (Apr 8, 2009)

Be sure to change the entire pump kit on these bigger yamahas! ( you only have to change the upper housing if it has <U>any</U> signs of melting.) <U>Never</U> change just the impeller! The poppet vavle, when working properly, will stay closed until the water<U>pressure</U> in the block is highenough to unseat the poppet valve. the excess water will dump staight down the sides of the tuner & out the exhaust. The thermostats are getting better, so be sure & use the latest supersession part number! Don't overlook the thermoswitch cavities having enough fresh diaelectric grease in them so theydo'nt give false readings. I have seen the cooling passages in the heads packed with corrosion not letting enough water to pass, but this is usually a top end overheat culprit. Good Luck!


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