1977 115 Alarm at WOT

[dacostadesigns]

I have a 77 - 115 which runs fine and can run all day at 3/4 throttle. On last two outings I opened it up (WOT) for a very short instance and the alarm went off. It has a 1yr old water pump and flows great. Looking for advice.

 

[racerone]

But the tell tale water does NOT circulate through the block.----It tells you the water pump is working.----It does not indicate proper cooling.

 

[F_R]

Pressure relief valve may be stuck shut?