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2003 225-4 stroke Honda overheat alarm at 2500 rpm’s. Or greater running for about 5min.

When is the last time you changed the water pump?

Pull codes. Procedure is attached and what the codes mean are attached.
 

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  • Procedure for Getting Fault Codes.pdf
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  • MIL Fault Codes Scanned.pdf
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I have no codes. My water pump is one year old and I change the two thermostats which one was bad. I still have the same problem. Will a bad relief valve do this.
 
OK. First check the starboard thermostat. They do go bad sometimes for no good reason. You can try running it for a while with the T-stat removed and check manifold with an IR heat gun.

If no help, pull the pressure relief valve. See: part #7 and the parts around it.

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That cover has three bolts, to remove it you only need to remove the two outer bolts. The inside bolt just holds the cover together. Check the hose to it, too. Typically, you do not need to replace the parts, just clean them well.

The manifold should be 160F when fully warmed up.

If that doesn't fix it, you will likely need to remove the starboard manifold.
 
Once you remove the two bolts on the relief valve, it will probably still feel like it's bolted in. You'll be tempted to try to spend 10 minutes pulling that last bolt because it must still be bolted in given that it doesn't budge when you pry like crazy.

But it's probably just corroded or stuck on there crazy tight. Just slowly work your way around it, prying it until it gives.

And i think these relief valves are very important to check, even if you're not getting an overheat alarm. Maybe it's just a coincidence on the engines I've worked on, just mine and a friend's, but I've pulled three bad cylinder heads, and every time, the relief valve was clogged with sand or stuck and had apparently been so for some time. My very unscientific view is that if the relief valve doesn't function over a few years, the head runs too hot and has issues.
 
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