Overheating 85 hp yamaha

[popeye]

ok new impeller,thermo, flused over and over with salt away, head pulled passages cleaned,broke three bolts re tapped what a pain.

AND STILL overheats at high rpm,, I have been told of a rubber gromet under the power head to connect the water tube, that goes bad with these motors. any thought sor suggestions please thank you

Popeye in Sarasota

[Ken]

Popeye,
On my C115, which is a V-4 block, there is a pressure relief valve in the cooling system. If this valve gets stuck open (from salt/sand deposits, debris, etc.) it will allow the water from the water pump to bypass the cylinder assy. and head and dump prematurely. I assume the three cylinder you have has a PRV valve also. Might want to check it.
Also, make sure you don't have a bad thermo switch giving you an early temp warning - they are fairly easy to check. Should close around 180 degress f. I had one that was closing on me around 135.
Good luck,
Ken K

[popeye]

thanks ken I have checked it,, and the water stops pumping at high speeds the alarm goes off and I slow down,, the water then pumps.

[Ken]

Popeye,
Sounds like the water intake area on the lower unit is gettng above the water line when you are at high speeds. Have you recently installed this motor? Added a jackplate? Maybe the motor is mounted too high on the transom?
Good luck,
Ken K

[jb123]

i had sporatic probs like that when i was max trimmed up with a pro v, yammies need plenty of water flow.

[popeye]

Thnaks I have thought about that but it is a boat motor package proline 16 foot stock, any suggestions if this is the problem other then droping the motor?? thanks very much

[Ken]

popeye,
While you are up on plane, trimmed out and going the speed needed to get the motor to overheat, have someone steer the boat while you look at the cavitation plate of the motor. It should be right at the waterline. If it is a couple of inches above the waterline, then the motor is mounted too high on the transom and the water pump intake is sucking air. No cure for this other than dropping motor down to next holes in bracket - or mounting motor on a jackplate. If you bought the boat recently from a dealer, they should help you with this.
Good luck,
Ken K

[popeye]

thanks i have a better solution I will have my 350lb girfirend hang her butt of the back at speed and this will drop the transon a foot,, ok ok just kidding,, i am so frustrated and appreciate your help, will try this asap

[Ken]

popeye,
Well, there's your problem! No wonder your transom was sticking up higher than your bow - 350 pound girlfriend riding up front! (just kidding, of course).
You never did say if this was a used boat just recently purchased - or if this problem just appeared out of nowhere after running fine for x-number of years.
Give us a little more information, Popeye!
Ken K