fastformula
New member
The engines are 500HP's which are the blue Mercury racing 502's. Ran the boat last fall, everything was fine. First time out this year the high temp alarm went off. I changed stats and still having temp issues. There are a couple other strange things going on. The water pressure on both engines always ran about 10 to15lbs at speed. Now both engines bury the needle at 30lbs at speed. Also, the temp gages will hang at 100 degrees, then drift up to 180, then drift back down to 100. The gauge does not read hot, but the alarm gets triggered. I replaced the impellers last fall, and there is plenty of water exiting the exhaust tips. The engines have Hardin exhaust manifolds with jacketed thru hull risers. I have changed thermostats, but both engines still have high water pressure and gauge fluctuation. One engine still sets the high temp alarm. I am a pretty proficient mechanic, but this has got me stumped. Any suggestions ?