I have a hp 500 that has low water pressure at idle and temp goes up. I took apart the raw water pump and the impeller was toast. Installed new impeller and housing and went back out, temp started to rise again at idle only. When i raise the rpm's the water pressure rises and the temp goes down. Put the boat back on the lift and ran it through the flush system and it idles without temp going up. Put the boat back in the water and pressure dropped and temp rose again. I back flushed the drive and water came out strong. I would appreciate any help with this problem. Also I had plety of water pressure when running boat, this only happens at idle......... Thanks

maybe a Piece of impeller down stream .. at idle it wont push enough water to cool it ....your flush system built in ? it might be ahead of where the plug is ....

I would follow the raw water line after the sea pump. Whichever cooler it goes to first, take the line off and check for impeller pieces.

My boat did the same thing last spring. The impeller pieces were blocking downstream. It would heat up whenever I got in no wake zones but as soon as I got out moving it was fine. The pickup on the outdrive could have something inside blocking flow at low speed too but if you flushed and it was fine it has to be further in.

Disconnect both hoses from your oil cooler and look through it. Clean as needed, or push a shirt hanger through if a piece is stuck. do not need to disconnect the oil lines, this is where most pieces get lodged. Back flush it from the far side, then back flush the feed line to the raw water pump and count the pieces, you should be able to account for most of the chunkies.

Good Luck
Shawn

take the water hose off from the crossover or the inlet at the water neck and back flush all the pieces from your busted impeller that are stuck in your oil cooler.

I did back flush it several times, it comes out strong and clean, i also took the pump apart and checked the new impeller and it is still good. I ran the motor on the hose through the flush and got about 2 pounds of pressure at an idle and it shoots right up with the rpm increase. I also ran the water through the drive and same result. What is an exceptable reading at an idle? I ran it for a while and it did not over heat, when it warms up a little i while take it out and check it again. Thanks for your help.

have you checked the thermostat ? could be hung just barely open ?

Those little rubber blades on the impeller went somewhere and they are in the cooler. Make sure you have as many of those little pieces as possible.

Impeller pieces, I agree as well.