Freshly Rebuilt 2.5 150 alarm please help

[Gsmith223]

The motor is an 1997 Mercury 150. Serial number is 0D275859 but the powerhead was rebuilt just recently and the EFI and oil injection was removed at that time. It now is premix and carbed.
I bought the motor and I am in the process of breaking it in but when I go above 3500 RPM for a few minutes I get a continuous alarm. I can come down off plane idle for 30 seconds and it goes away.
The motor has a new impeller and the pee stream looks good. The motor doesn't appear to be overheating but I dont have a water pressure gauge or temp gauge to confirm this. The guy who built it is very old school and said he has done many rebuilds of the EFI and put carbs on them so I hope it was done right. He test ran the motor for several hours and said it never got hot on him but he just used his hand to check it. He thinks its an electrical issue. I plan to take it out again, run it and check the temp with an IR gun.

My first question is where is best to tap into the motor for the water pressure gauge? On my last one it was a tee in the pee stream hose but I heard that is not a good spot?

Next I want to install a temp gauge I know where the sending unit goes on the head but I would like to use a digital gauge if possible? Does anyone know of a digital gauge and sending unit that will work?

If I find out the motor is not getting hot is it possible the alarm is something else. I still have my oil tank in the boat and but I dont think anything is hooked up.

Any help is greatly appreciated

[150aintenuff]

water pressure goes on transfer from poppet to top of block line and sounds like you may have a faulty alarm hcylinder head sensor if it is infact NOT getting hot.

CONSTANT alarm on those is only over heat

[Gsmith223]

Checked temp when alarm is going off and I am getting about 180 at on the head in different places. I am getting 15 psi water pressure but I still get the alarm. Any way to check the alarm sensor?
Is 180 to hot?

[XstreamVking]

That's hot

[Gsmith223]

That's hot

Thats what I thought but had a guy tell the alarm shouldn't kick in till 210.
I plan to replace the impeller, and poppet valve. I dont have T-stats so no issue there.

[XstreamVking]

My 2.5's run about 140 on the block with my IR gun and on my livorsi gauge that reads cyl head temp. I have been told that 190 is the hot horn trigger point.

[tlwjkw]

190 to 210 supposedly ... probably depends on what day of tha week they were built.. put t-stats back in it... thats what they were made for.. do "complete" oem pump kit if you didn't before.

[tunnelmike]

With no thermostats or the washers in place the water sometimes passes thru the motor too fast to remove the heat. Could the motor be too high ?

[Gsmith223]

The motor is mounted the same place as its always been so I dont think its running to high. I will put the T-stats back in and see what happens. I have the water pump done and will be putting the LU back on shortly.