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97 yamaha Pro V 150 overheat issue


Bout Time 1
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Lately I ‘ve been getting the overheat alarm and then Limp mode only at high RPM, like close to WOT. If I shut it down, wait 30 seconds and turn the key on, the alarm goes off and I can run all day under 4500 rpm. I started out by changing thermostats,  checking the poppet valve (old style) and cleaning it. No change. Recently put a new water pump in. No change. Checked both thermo switches per the repair manual. They are both good. Pulled the heads and checked all water jackets. Some minor blocked areas but have always flushed with ears with fresh water after running in salt. Heads looked pretty good. Cleaned everything up and installed new head gaskets. I also installed the new mushroom style poppet valve. I’m hoping I finLly got this solved but cold and rainy here so no trial run yet. Had anyone had a similar problem? Could it be the poppet valve? I swear the old one looked fine. Thanks. 

PS  this engine has 588 hrs on it  

 

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The new poppet is a big improvement over the old style.  Yamahas are very sensitive to blockage in the water jacket passages.  I plastic bead blast the heads and jacket covers to get rid of all the scale and build up.  I also lap the heads flat again.  Try Mary Kate On/Off in a squirt bottle for the passages in the block. use lots of water to clean it all out.  Hopefully your issue isn't a corrosion hole in the exhaust plate mixing exhaust and cooling water.

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Had the same engine ,same yr.  It is a great engine,  mine finally died of  water jacket corrosion. I never had a over heating alarm.  Mine was kept in water at a brackish water marina.  Hope yours is ok,600 hrs is nothing for that engine.  Mine had well  over 1500 hrs. You just don't that power sound from the 4 strokes.

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  • 2 weeks later...

Well finally got it out today. Ran it WOT up the ditch and it never overheated. That’s a plus. However the last couple times I’ve taken it out it has been smoking from under the powerhead and today I recorded the leak. Looks like the powerhead is coming off to change the exhaust seal which also has the water tube from the water pump running thru it. Does not leak like this when running at home with the ears on. Just when its in the water. B-O-A-T.....lol

31E1947A-FC65-421C-9CEE-291BAD3219AC.MOV

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  • 2 weeks later...

Update:

Took my boat to a mechanic here in Jax cuz I didn’t want to tackle pulling the power head. Even though I changed the poppet valve, once he got the powerhead off he found that the other end of the hose from the poppet valve spring assembly was clogged solid. Also the power head gasket was roached. He charged me 300.00 labor and about 60 bucks in parts for the gasket, a new hose and the nipple on the return end of the hose. I think I got off cheap! I should be good for awhile now!! Glad no holes in block or exhaust plate! Dude is a solid fair mechanic! Thanks Chris!!

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6 minutes ago, lurem said:

Is that spring and valve what everyone is calling a poppet valve? What is its function? Besides clogging with salt deposits and causing us grief? Haha

Poppet valve allows cool water to stay in the block while idling or running at very low RPM.  The poppet opens (from pressure) at higher RPM when the flow from the water pump is a lot more.

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14 hours ago, Bout Time 1 said:

Update:

Took my boat to a mechanic here in Jax cuz I didn’t want to tackle pulling the power head. Even though I changed the poppet valve, once he got the powerhead off he found that the other end of the hose from the poppet valve spring assembly was clogged solid. Also the power head gasket was roached. He charged me 300.00 labor and about 60 bucks in parts for the gasket, a new hose and the nipple on the return end of the hose. I think I got off cheap! I should be good for awhile now!! Glad no holes in block or exhaust plate! Dude is a solid fair mechanic! Thanks Chris!!

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Indeed you got a fair deal there!  I assume he didn't break any bolts which is rare on an aged Yamaha.  Only thing I may have opted for would have been new upper motor mounts since he was in there. The rubber looks pretty tired. 

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