94' 150HP 2 Stroke Alarm- Cooling or Oil?

I have a 150HP 2 stroke motor on 1994 Grady White. had the carbs cleaned out and ran it 6 times on Cape Cod few weeks ago and and it ran flawlessly. I brought it back to NY two weeks later and started it in my driveway with earmuffs on and I noticed no cooling pee stream and the alarm then sounded.

I turned the motor off and let it cool down, I then submerged the lower unit of engine in a 40 gallon container thinking maybe with earmuffs it was not getting enough water and tried it again, at first no pee stream then a weak one, followed by the alarm once more. I turned the engine off again. I brought the boat to a Yamaha dealer, they replaced the water pump and tired it again the same result however- the alarm once again sounded with a weak pee stream.

The boat is still in the shop, they plan on removing the engine heads, they think there is blockage on the right side of the engine. Is this the next logical step? The thought is that there is blockage as a result of salt water scale and salt build-up. I noticed that there is a triagle above what I think is the oil gauge- it's the round circle that's almost entirely black? Could the alarm not be a result of overheating but rather with the oil delivery system? Both the aux. and main oil resevoirs are full, I did notice that after the carbs got cleaned that the boat seemed to use less oil- not sure if this is a cooincidence or not? Any help would be appreciated....

[boats.net]

If the thermostats and pressure control valve are ok then the heads would be the next step. If it's oil alarm then the red oil light would be on in tach, the green oil light should be on if tanks are full.

Hey thanks for the feedback, I'm in even deeper now however. I asked them to check the thermostats and pressure control valve, they had hit the heads with a temp gun, they had a 40 degree hotter right side than left so they thought it was blockage and inadequte cooling... as a result they pulled the heads- they were pretty clean no scale and only moderate carbon bulidup- but no blockage. The shop (Yamaha Dealer) is waiting for new gaskets and they are going to button her back up.

I am not sure what the next steps will be but my wallet is sure going to take a wallop, if any one has and ideas on the next steps I sure could use the help? I will ask them again to check the thermostats and pressure control valve, any thoughts on the temp differential?

[camocajun]

i have the same motor and had same problems. it was the pressure con***** valves.replaced them and the overheating went away. however she still doesn't like to run on the ear muffs for more than 2-3 min. but put her in the water and she runs fine all day.

[tomdion3]

Did pulling the heads and clean the water jackets solve your overheating problem?

[Hamfisted]

Pressure control valve...

Yamaha came out with an redesigned pressure control valve in '06. Make sure they install the updated "Mushroom Headed" pressure control valve in your motors and not re-install the stock old style. The old ones got stuck open a lot, and when that happens you lose all your cooling water out the relief hose instead of filling up the powerhead jackets with water. Maybe your local shop doesn't see it a lot up there, but down here it's epidemic. If you ever crank up your motors and see cooling water coming out the vents above the cavitation plate while the motor is still cold it's most likely your pressure control valve stuck open and you're going to have cooling problems. Now, when the motor warms up you're going to see water flow out those vents, but it will be hot water. There should be none coming out when the motor is cold.



- Mike

[tomdion3]

Pressure Control Value - Overheating

I'm not sure I get how the Pressure Control Valve (PRV) works yet... If I understand this post and previous post, then when the motor is started and runs at idle at around 800 RPMs - the water pressure is around 5 psi - the PRV should be closed - and you should see no water dumping out the relief holes at the top and back of the upper casing...

When you bring the motor up to around 3000 RPMs or above - the water pressure increases to around 20 PSI or higher - at this point the PRV begins to open by pushing or depressing or compressing the spring in the PRV Cover Housing to relief water pressure - and you should starts to see water dumping out the relief holes at the top and back of the upper casing...

What I don't get is why the increased water pressure at 3000 RPMs or above causes the engine to overheat... Doesn't the increased pressure mean that more water is being provided to the water jackets surrounding the cylinder heads keeping them cool? Sorry for being such a novice to engine operations...

[boats.net]

Most all Yamaha cooling system are high volume low pressure systems, the V6 engines requires a lot of water to fill engine block and it has to have pressure to fill all water jackets. The pressure control valve is just a pressure relief valve and will remain closed until pressure reaches about 25 psi and then opens until pressure drops below 25. An open valve or a restriction in water passages will result in not enough water to keep engine or parts of engine block to keep cool. The higher the rpm's the hotter the engine runs and requires a high volume of water to be circulated.

[brougham]

Hey guys,

I'm new to the forum, and just recentlly purchased a 92 Maverick with a 92 130 yamaha. I've been dealing with the issue of overheat alarm at high rpm's (4000+) also. I've been trying to do the repairs myself with some success, lots of fun. I've purchused PCV, spring, and gasket. I need your help with how to install. Pictures would be awesome. Thanks

[99yam40]

You have added to an old thread. you need to start your own thread by clicking on the Create new thread button on the top of the page.

[cyrillefrenchy]

i have seen some intake water pipe ( copper pipe between water pump cap and powerhead) half clogged up with chunks of old broked impellar.
if you have bad impellar and some blades are gone, make sure you get them out of the copper pipe.
to see if the pipe is clear, i put a piece of rubber hose over the copper pipe and blow with my mouth so i can feel if the pipe is clear, free of clogg.
do not blow with compressed air you will push the pieces inside the powerhead.
you can check if the pipe is clear with a piece of threaded rod or something.