1996 Yamaha C115 - low water pressure problem

[hawilson2]

I have a 1996 Yamaha C115. I am experiencing<br />low water pressure in both cylinder heads. I have 2 water pressure guages installed and both show low pressure after reaching around 1400 RPM both in gear and not in gear. Because both cylinder heads show the problem, I have ruled out the thermostats which are each 1 year old. That RPM seems to be right around the magic number. The pressure reaches ~16psi and ~14 psi before dropping to ~7 psi and ~2 psi when ~1400 or above RPM is reached. My first attempt at a fix involved replacing the poppet (pressure relief) valve, grommet, spring, and gasket. It did not help. I have checked the water pressure guage lines and they show no signs of leaks. The water pump is 2 years old and is my next line of attack unless anyone can come up with<br />something else. Compression in all cylinders seem fine measuring what they did before all this started happening. I get no overheat buzzers and I can touch the powerheads to a count of 10 without burning my hands. It seems enough water is getting through to keep temp low enough. Any suggestions would be appreciated. Sorry about the long post but I am trying to include all the facts.

 

[hawilson2]

Re: 1996 Yamaha C115 - low water pressure problem

r

 

[rodbolt]

Re: 1996 Yamaha C115 - low water pressure problem

replace the t-stats and water pump they are about due. they dont last foever. but if the engine is staying cool dont sweat the specific numbers to much. is this something that just occured or has it always been like this?<br /> good luck and keep posting

 

[hawilson2]

Re: 1996 Yamaha C115 - low water pressure problem

I am replacing the water pump this weekend. This is something new that started happening last Monday. Until then I normally ran ~20 psi and 16 psi. Last Sunday I did replace the lower unit oil but I can't imagine that could cause this type of problem. Thanks for the reply.

 

[tryan]

Re: 1996 Yamaha C115 - low water pressure problem

it sounds like the inner hub of the impeller has sheared off the rubber. ie once pressure builds, it starts to slip.<br /><br />re-assemble with the proper dressings and lubes to make it easier next time.

 

[hawilson2]

Re: 1996 Yamaha C115 - low water pressure problem

I changed the water pump and all is great. The<br />inner hub of the impeller had in fact sheered off<br />and would slip when high enough RPM was reached.<br />Thanks to all who responded.