Just did an impellar job on my HP500's. After assembly we put them on the hose and started them up. Water flow out of the exhaust was excellent. However once the engines began to warm up the temperature gauges on both engines would fluctuate between 100 and 150 like slow windshield wipers, by that i mean they would go from 100 to 150 then back to 100 (cycle repeats) within a matter of 3-4 seconds??? What is this and why is it doing that??? Also one of the engines after about 5 minutes of idling the audio warning buzzer would sound. I know its not low drive oil or low oil pressure, and I've already described engine temp, could it be a piece of the old impellar is lodged somewhere in the engine? We tried to backflush the engine and thought we had all the old pieces out? Where do I go from here?

Check for impeller pices lodged in the oil cooler or thermostat. It could restrict the flow of cool water to the engine Jamie / Lakeside Restorations

I would not worry about it. It is just because it is running on the hose. My engine/525SC does the exact same thing with the temp fluctuation when running on a hose.

Yea, What Griff said!!

what donzi said, I would back flush the system to make shure there are no pieces any where ( in the coolers )


that should take care of any issues

And don't just back flush with the water hose, take the supply hose off and check.

were chunks of the impeller you replaced missing any vanes?

yes, strangely they were both fine one weekend and the next completly destroyed when i started up, no water flow out the exhaust, when i pulle the impellar housing both of them were scorched, destroyed completly, i think the marina started the engines with the seacocks closed as i left them that way.... So you're saying the hose is causing the temp fluctuations or the alarm to sound? I'm thinking maybe air pockets in the engine from changing impellars as we took off several hoses to access impellar housing bolts. So i'll try taking apart thermo hosing to see for pieces stuck in thermo or ball valves, then fill engine with water, so no air pockets? Should I backflush with water or compressed air?

I'dpull the supply lines to the oil cooler first probably find peices of the impeler in there restricting flow. Its happened to my engines three times in the last six months.

Miami, When you figure it out, please let me know. Mine does the same exact thing but does not trip the alarm. Maybe it would after 5 minutes, but I never ran it that long. It seems to work ok, but im never sure if I'm going to overheat the motors while on the flush. I have 2000 HP 500 carb motors. When I run the boat on the flush the temp guages float. My flush system does not have manual valves to open and close, Im told there is a built in check valve.