Yamaha F250 running hot

[Lawsup]

Yamaha F250 is running hot due to loss of water pressure at higher rpm's 4500-6000. I can gently come on plane and cruise all day at ~4200 revs and all is well and i am holding 18-20psi on WP gauge. Trouble starts when i go above cruise speeds the pressure gauge slowly falls to 0,piss stream stops and engine will overheat. I can slow back down to around 2k and the pressure returns to normal. I have put over 100 trouble free hrs on this motor this spring and this just sarted after a slight mud bogging event followed by a COMPLETE yamaha WP repair kit was installed including the cup and a thorough flushig/saltaway.

I pulled the pcv valve and it is now clean and appears to be in working order.
pulled and cleaned T-Stats, looked fairly new so they were reinstalled
pulled lower unit multiple times to inspect WP area and for exhaust corrosion, i see no issues.
I can run the motor all the way up on jack plate and down and it doesnt seem to make a difference.

The boat is a 25 shearwater and the motor is a 09 F250 with approx 900 hrs.

I enjoy working on my own things but im out of options that i know of. Anybody care to help me out or put me in touch with somebody that may lead me in the right direction over the phone. If not its going to a shop shortly.

Thanks,
Preston 850-768-3191

[EddieJoe]

Did you pull the plate around the water flush port? My Suzi was overheating because the chamber around the port had corroded through and was leaking pressure into the exhaust. Don't know the setup on the Yam but it drove my mechanic crazy after he did the pump, the stats, and the overheat sensors.

[Jumptrout51]

It is worn out.
Give it to me and buy a new one.
At my age I can run under 4200rpm.

[Lawsup]

I could use a little more HP JT..
I'm going to get back on it tomm and hope I find something like you speak of on your Zukes

[fishinfool]

This is probably of no direct help, but just thinking out loud. It sounds like the impeller is cavitating at higher rpms. Possibly damaged out of the box or during install. I know it should be lubed and the drive shaft turned in the direction of motor rotation when seating it in the cup. Possibly it is spinning on the shaft on higher revs. The only other thing that comes to mind is the water inlet is sucking air at higher revs. Since this was not an issue prior to the new WP kit, I think it is less likely.
Good luck and let us know what solves the problem.

[EddieJoe]

I could use a little more HP JT..
I'm going to get back on it tomm and hope I find something like you speak of on your Zukes

Here is what it looked like.

EJ

[Double Naught]

Lawsup, I'm not a marine mechanic, and like you, I work on my own stuff a lot.

Seems if you hot water tested the thermostats and are sure the poppet check valve is opening all the way, you've done the easy part.

Then as said by others:

water pump/impeller - broken fins, drive key problem, air leak on intake side, partial water intake blockage.
loss of pressure into the exhaust - corrosion, gaskets, cracks

You probably know this but just in case... head gasket leaks can also push vapor into the cooling system and cause a serious loss of cooling efficiency... more rpms equals more vapor. Once the cylinders walls reach a critical temperature, steam bubbles erupt on the cylinder walls insulating them. The steam conversion will cool the cylinders a little bit, never as good as water contact though. This steam insulation prevents effective cooling of the cylinder walls until the heat source is eliminated. Temperatures can soar quickly. That is hopefully not your issue, but keep it in mind as you test the motor. You could get into serious damage if not attended to. You had said nothing comes out but steam. Be aware that no matter the cause, that steam is coming off your cylinder walls. Nothing good can come of it.

Good luck and post the solution when you figure it out.

[Lawsup]

I Think I've found the problem. The gasket and stainless plate under the impeller doesn't completely cover up or seal off the suction side of the system. There is a gap on both sides,one pictured worse than the other. Air could pull in by the plate when water starts being pulled hard and cause cavitation.I either have the wrong plate/gasket for my year model or my foot isn't the year model of my motor. I bought the boat this past winter with unknown history.

[Lawsup]

It's the little gap just above the bottom right dowell pin. I filled in both gaps with some grey silicone and plan on letting it dry overnight and I'm going to run it on the lake tomm. If that fixes the issue then I will do some digging and find out what I need to do about getting the correct plate for a permanent fix. I also installed 2 new Yamaha Tstats while I was at it today..
THANKS TO ALL.

[fishinfool]

Yup, looks like the wrong gasket for sure. the guys at Capital Rubber & Industrial Supply 130 Progress Dr, Tallahassee, FL 32304 (850) 575-1811 can make you a custom gasket if you have a hard time locating the right one,very reasonably priced. Also Pete at Sunshine Boats can be of great help locating parts.
When replacing the gasket you might want to use a brass brush to remove the loose paint and corrosion. It can cause leaks. It has caused me a few headaches in the past with auto repairs.

[Lawsup]

Well the silicone coated around the holes fixed the issue. Run her up to 5900 rpm for quite a while with no loss of pressure. even run it all the way up on the jack plate and didnt loos WP at point of cavitation.. Im saying i have the wrong part but the parts guy in panama says thats all he has listed and no other year model is even close... I dont want to leave it like it is but i can't seem to find the right part. Wish i didnt throw the old plate and gasket away but they are probabaly recycled by now.

Its not just the gasket, the stainless plate follows that line also.

[fishinfool]

I had an old Yammy 25 that I replaced the head gasket on. The new gasket did not follow the old exactly, but covered where it needed to in order to do the job. I think it was a design change of some sort. If it works, use it. There is no reasoning with engineers sometimes.

[Bluewave]

You might want to rethink the silicone in my work on semi trucks some of the silicone could break loose and stop up the water ports and then you would have big problems. I would rather get the correct gasket or have one made as the other guy said. Could save you a bigger problem later!

[Lawsup]

I did bluewave.. made my own today. Im going to put a little film of silicone on the new gasket and replace the screens on the front of the nosecone and call it good.. Hopefully it will perform and the snaps will be biting sat!

[Bluewave]

I hope so too we a heading back to Ecofina Sat as well hope something is biting this week been tough!