jbrauer

I'm running stock 1995 HP500-Carbs, Low Water Pick-ups, 30' cat, 10 - 15 lbs. water pressure at speed.

Last weekend the port motor temp started acting wierd. It starts and idles normally and reaches thermostat temp of 140. Then the temp drop to the bottom of the gauge, goes back to 150, drops to bottom, goes back to 150, over and over. After a minute or two of this, the 180 degree alarm goes of and I shut down. There is normal water coming out the exhaust ad the sea strainer looks like normal water is being pulled in to the motor. If you get on plane before the wierd stuff starts, the motor is fine and the temp stays normal at 140 - 150. Once on plane water pressure is the same as it ever was, at 15 max.

No sign of water in the oil. So far we've completely rebuilt the raw water pump including impeller, plates, bearings and seals, replaced the thermostat and confimed the riser check valves (white plastic balls inside the thermostat housing) were functioning good, and replaced the recirculating pump. It still acts the same whether in the lake or on the garden hose.

I'm lost! Anybody seen this before?? Help!!!

BadDog

Do you have holes in the T-stat? I am using a crossover with T-stat and dump valves. Without the correct size and number of holes my temp gauge looked like a windshield wiper unless I was on plane.

jbrauer

Hmmmm...

I installed the factory Merc T-stat, same as the one I removed. Neither has any holes and it was fine before now.

Jeff