Yamaha overheat alarm

[104460RSo]

Hi,

Got a 2006 Yamaha v150tlr Vmax outboard, if running above 4000rpm the overheat alarm goes on and rpm is cut to 2000rpm.
Have now replaced thermostats, waterpump, headgaskets, poppet valve, cleaned waterjackets heads etc. Still alarm comes on minutes after passing 4000rpm
Also installed a gauge on water pressure, pressure is ok.
thermoswitches open at 82 degrees.
anybody know what could be the problem?

[ausnoelm]

Still got a blockage somewhere, you sure you dug out all the crap from ALL the water passages? did you replace the full water pump, or just the impellor?

[104460RSo]

Both heads and water jackets have been cleaned...there was a lot to remove/dig out on the top left side, near the thermostat, I was sure this was the problem.
Also cleaned around the cylinder bores.
I have connected my pressure gauge with a hose on the top left bank, water pressure seems to be good at all time and all rpm. I did replace full water pump and oil seals under the pump.
Where else could there be a blockage for the cooling water?
My plan is to stick two PT100 temp.sensor, one on each head today, then i can see the temp on each side when motor is running above 4000rpm, and then maybe spot the problem

[104460RSo]

Update!
I put a lot of Thermax surface temperature indicating strips all over the heads and water jackets. Went for trip in the boat and as soon i hit 4000rpm the alarm comes on and motor goes into limp mode.
went back in and removed the motor cover, saw right away that all my temperature strips had gone up to 98-101 degree Celsius, this is on both heads and on both water jacket covers. Im sure my water pressure was about 25PSi just before the alarm came on, forgot to look at the gauge when the alarm came on.
so, what does this mean? Do I got a blockage somewhere?

[99yam40]

Could the water intake suck air when getting up to speed.
But then the pressure gauge should show if that is happening.

If you verify the water pressure stay good, I would be looking for something like Rydlyme marine descaler to see if that would get to the stuff you could not manually cleaning

[104460RSo]

Motor is not sitting to high om the transome , I don't belive it is sucking air. Intake was also cleaned when I did the waterpump. But I will go out and verify the water pressure when the alarm comes on, I need to know before I do anything else .
I have seen some videos og people using Rydlyme and other water scale removers, seems to work good.

Any suggestions where else there could be a blockage on my motor? Somewhere between the lower unit and the powerhead? Any of you Yamaha owners had same problems as me?

[ausnoelm]

Could be a bit of an old impellor? have you removed the exhaust covers and looked for blockages? I have found all these miracle products (including vinegar) don't work all that well to clear blockages, but are OK as a preventative, but, it's worth a try, not as good as mechanically digging it out though.

[104460RSo]

The old impellor was in good condition, nothing was missing.
I have not removed the exhaust covers, only inspected what I could see through the hole for the poppet (and that's not much)
I think I will remove the covers and have look....thank you for that information

[99yam40]

I have helped 2 different motors(a C60 and a 90) stop getting a high RPM overheat by dropping the lower unit, hooking up a water hose to pipe heading to power head, removing the stat, turning water on full blast, and injecting some compressed air into the water hose off and on while flushing.
I believe it helped move some build up if sand in the bottom of the block.

[Gary4731]

I have the same problem . . .only in the opposite: My 2001 OX66 SX250TXRZ sounds off when I ***** slowly or idle for a few minutes. I slowly accelerate for about 30 seconds and it goes away. The stream out of the "P" hole is steady, although kinda thin. The motor is clean and was just recently introduced to salt water from its fresh water lake existence. Otherwise, it runs like a top. Any thoughts? Thanks in advance.

[ausnoelm]

Start another thread rather than latch onto this one, everything gets mixed up when talking about two motors, two owners and two faults.

[104460RSo]

I now know that the motor is loosing water pressure right before the overheat alarm comes on. Tested today, water pressure is good up to 3800rpm.....as soon i goes above 4000rpm, the pressure drops to 0. After few seconds on idle, the water pressure is back.
what will be the next thing for me to do? Remove exhaust covers? Should I drop the lower unit and try to flush it with a hose connected to the pipe that is going up to the power head?

[99yam40]

if water pressure drops to Zero, flushing and blockage is not the problem.

I still have a feeling there is some turbulance happening under the boat causing air to be sucked into the water intake or pick up is coming out of water.

did you check to make sure the dampener next to water pump is not letting exhaust by to get to the water pump
the rubber dampener and its aluminum brace do go bad and not seal properly sometines

[104460RSo]

Water pressure drops to zero yes.
Maybe I can put a gopro camera on the transome and have a look what is going on back there....

I got the small rubber dampener behinde the waterpump, it's not new, but it is there. But there is no aluminium brace as I remember....just the small rubber .

[104460RSo]

Isn't there suppose to be a gasket as well here? I sure i have seen that before on other outboards