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04 VMAX 2 stroke 150

Stratos 275

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New to the site and need a little help. I've got a Stratos 275 PRO XL with a Yamaha VMAX 150 2 stroke. Had an overheating alarm at full throttle, outboard tail tell was discharging ok. Replaced water pump, thermostats and pressure relief valve. Still overheating alarm. Right power head hot, pulled head and water cover plate, replaced both gaskets. Also did compression test, lowest cylinder was 109 highest cylinder was 114. With motor in a tank, water pump is excellent, have water at both t-stats. Launched to put motor under load, overheated again at full throttle. Noticed steam coming out of exhaust ports. Thinking next step is to pull exhaust manifold. Inner exhaust cover was replaced about 100 hrs ago about a year ago which had minor pitting allowing water to enter dry exhaust side. Anyone else had a similar issue? Thanks.
VMAX 150
 
Are you getting high temp alarm only @ WOT?...does alarm remain on when you back off throttle? When you pulled heads off, what was the condition of the water passages? If there was corrosion, it's possible corrosion has also built up behind block. A little steam from exhaust isn't too concerning, especially from a 2 stroke. I'd also test the temp alarm to be certain the alarm is not a false positive. When troubleshooting a possible high temp issue, unfortunately the water exiting the T/T is only indicative of a functtional water pump...it's not indicative however the pump is able to circulate water throughout the cooling passages. And as you've discovered, testing engine for high temp alarm when not under load is futile. I'd start first with confirming the alarm is indeed being grounded by high temp, then perhaps flush with salt-x or likewise product to try to break up any corrosion.
 
ClassicAQ,
Thanks for the reply. High temp alarm is basically anything over 4k I've discovered. Once the alarm sounds and I throttle back to neutral and leaving the engine running the alarm will silence in about 30 seconds or so. Pulled both heads yesterday, a lot of scale around the water passages. I cleaned the passages around the pistons as well as the heads and water cover plates. I'm also replacing the primer bulb and hose assembly as it's 14 yrs old and I know an overheat can also be from running lean. Will test temp switches today.
 
Update, used Muriatic acid and cleaned cylinders while heads were off as well as an acid bath for the heads. New gaskets and off to the races. Thanks again for the replies.
 
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