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'96 175 hp running hot-need opinions

B

backbays

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The motor ran fine last season. New impellor installed prior to launch this spring. Motor running hot from first time out. I put in new stats and flush motor with 1/2 gallon of muriatic acid (yeah, getting desperate) to five gallons of fresh water followed by baking soda and water mix and then ran motor for twenty minutes. Motor will run hot 1500 rpms to just under 4000 rpms. Laser thermal scan shows starboard running 10 degrees hotter than port side with readings between 160=190. Poppet valve kit done five years ago. Never any alarms. Carbureted motor used exclusively in salt water, good compression, I don't believe there's a ton of hours on it, and the motor pulls strong. Normal stream (no steaming) from the tell tale especially when I tried without the thermostats. I'm torn between calling it a season and really disappointing guests staying with us, or just use the boat and try to avoid those hot rpm spots. Any suggestions to resolve the running hot dilemma or whether to just run and pray?
 
Thank you for your timely response. The impellor was a Mercury kit with housing and gaskets (50+dollars). The lower part was changed perhaps four years ago. I will jump on the poppet valve right away. I wasn't really considering because I didn't know it needed attention that frequently (appreciate the advice) and that the motor would run hot at such varying rpms. I'm on it.
 
Yikes. Logistical nightmare to move boat out of water now. Started on removing poppet valve but thunderstorms had other ideas (Jersey Shore; you had them too). Will finish that in the morning. Hoping a better water flow will address the hot running motor. I'm really concerned that blocked cooling passages are the real culprits. Would a four year old lower housing likely be the cause for running hot? Can't thank you enough for sharing your valued knowledge.
 
Well that's sure sobering news. A family is on their way up from
Virginia to stay with us for the week anticipating going out on the boat. Happy Fourth everyone#&*@!^%$.
 
Thanks for your concern. Poppet valve may have helped a bit. I've resigned myself to staying at rpms that keep it manageable (under 1200 rpms or over 3700 rpms). Those in between rpms can spike the temps up. Thinking a twenty year outboard in salt water may have some blockage problems.
 
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