1990 Yamaha 2 stroke 85hp Alarm at higher RPMs

[spunkyman]

Having an alarm issue with my Dad's boat, a 1990 Yamaha 85hp 2 stroke (model CV85ELD) . Completely rebuilt 3 years ago with powerhead rebuild kit, new impeller, thermo, poppet, s park plugs, shift shaft and control cable. For what ever reason, this guy starts to overheat in the high RPMs (no gauge to tell exactly what RPM). The prop is new, I believe its a 15 pitch. Water pees out the hole as it should. Usually, if I stop, it will cool down a bit after a few mins and I can start to use again at lower rpm once it cools a bit, but I'm not sure what else I can possibly do here. Either, somewhere, the water isn't flowing enough, or maybe a sensor or something?

 

[Sea Rider]

When the alarm sounds is there a rpm reduction to safe mode when overheats ? Have you changed the thermo switch, could be culprit and firing prematurely....

Happy Boating

 

[mike_i]

When were the water pump and thermostats replaced last? Just because water is coming from the pisser doesn't mean the water is circulating thru the motor. If the pump is three years old you got your moneys worth and it's time to be replaced. Are you in fresh or salt water?

 

[peterskeeter]

Water jackets may be plugged up with marine scale. It doesn't take long and even with flushing, it does little to keep it from building up.

I have a 1996 C85. When I moved to a different area of water, it took about 2-3 years to build up with scaling. It's mostly calcium carbonate. I removed all the build up by removing the head and exhaust side plate. Installed a block flusher like the newer boats come with and 3 years later, my inner exhaust baffle had to be changed due to just age. It was 20 years old and developed a pin hole letting water I to bottom cylinder. Anyway, it had only been 3 years when I changed the plate after starting with cleaned out water jackets. I religiously flushed the engine Everytime I got back home while lifting it out of the water. The amount of buildup I witnessed in 3 years was mind blowing.

Might want to try a descaler or play with a homebrew of muriatic acid diluted down to 10 parts water 1 part acid but use at your own risk and be very conservative. I've done it on my Yamaha 150 and it removed a ton of scale but was also nerve racking. I experimented on old Yamaha aluminum parts before doing anything

Just my 2 cents

 

[fullthrottle52]

This is a copy from another forum I was just reading. May help.

I've been chasing an overheat condition in my Mercruiser 4.3/Alpha power. Two new water pump impellors, risers, all new hoses, thermostats, gauge and sending unit. Above 3600 RPM the temp would start climbing up to around 190-200.

I was at the dealer picking up some parts and asked the tech if he had any suggestions. Right away he said to drop the lower unit and pull out the copper pipe that connects the water pump to the upper housing. Sure enough there was a 1/4" hole corroded through up at the top. He also said to pull out the rubber grommet that the pipe fits into and clean up any corrosion where it seats. He had seen them so corroded that it would squish the tube almost closed.

Got it all back together and it's running at 160 degrees regardless of RPM.

I've been Googling this issue and haven't seen any mention of looking at the cooling pipe.
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