Alarm noise on merc 2.5 EFI 280HP

[Kanookstr]

I have twin merc 2001 2.5 EFI sports 280HP. i have one that started making a continuous alarm noise after running for 5 min or so around 4500 and higher rpm. i would back off to an idle and it would stop. i thought it might be temp but i pulled off the cowl cover and the heads felt fine. i even checked the other engine and it felt the same.
Today i replaced the impeller just in case and it did the same thing, i did notice that even when the alarm is going on i can still run the engine at any rpm including WOT. I was told that if it were high water temp that the ECU would limit my rpms to below 5000 rpm. but i can reach 7000 even when the alarm is on??? any sugestions would be very helpfull.
thanks

[Jay Smith]

If your are running twins are both engines alarming ? If just one is alarming you have the perfect means of finding the issue, simply reverse the heat censers from the port to the starboard engine and if the issues follows the suspect bad censor you've got it... Also you might try heat gunning both engines at the same place on the engine after a run and see if the suspect engines is really hot..I use heat guns all the time they are a priceless tool..Also water pressure can cause issues, do the same with those censors too..

Cheers,
Jay

[Kanookstr]

good idea. thanks.