# Overheating Yamaha 150 HPDI- AGAIN



## NGaHurricane

RECAP: was out in the water the other day running about. Idled down to search for our waypoint and got a temp alarm in the port engine. Cut it off for about 20 minutes. Cranked back up and worked fine as long as rpms were above 1000. 

MY SOLUTIONS: After reading the forums, talking to other boaters we changed both thermostats and replaced the water pump gasket and impeller. 

RESULTS: Too out today and ran about 10 miles wide open, idled around for about 15 minutes. Ran for about another 5 miles and backed it down to "trolling" speed for 20 minutes with no alarm. I disengaged the the drive and we sat in the water with the engines idling for about 10 minutes and the F#$%ing alarm went off. We cut the motor off waited for 10 minutes fired it right bak up with no alarm. We put another 5-6 miles on the boat at 3/4 throttle and then idled back the last mile to the ramps. With NO ALARM. 

I am at a loss, what the heck is going on. short of a total engine breakdown and rebuild. What SUGGESTIONS OR ADVISE DOES ANYONE HAVE???


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## marmidor

What year is the motor?


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## TheCaptKen

You are going to need to put a pressure gauge on that engine to see what it's dropping to. Why didn't you replace the entire pump?


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## NGaHurricane

2001 twin 150 hpdi


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## markw4321

TheCaptKen said:


> You are going to need to put a pressure gauge on that engine to see what it's dropping to. Why didn't you replace the entire pump?


Before you do that check your poppit or poppet valve. Believe that motor has one and the symptoms you describe - overheat alarm at idle sound like a poppit valve. Google search it


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## NGaHurricane

The motors are 2001 150 HPDI's.

Went and bought a infared temp gague and it is showing the top cylinder on the right to be 30 degrees higher than the others. This is the cylinder just below the thermostat. We flushed with vinegar multiple times, then water again and still am showing an temp difference of 30 degerees. The other cylinders are running between 130-140 and this one was at 170+.

At this point I am assuming there is a blockage in the water jacket that when the psi is increased the water flows and keeps cylinder cool, but at low rpms it overheats.

QUESTION: How difficult is it to change the water jackets? Am I out of line in my line of thought?


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## markw4321

Hurricane

I had a 150 yamaha 2 stroke that was only sounding an overheat alarm at idle. Replaced thermostats etc. just like you. Turned out to be the poppet valve which is a spring loaded valve that can get salt build up and freeze open which causes an overheat symptom at idle. 
What happens is the valve is stuck open and water dumps out before reaching the upper cylinders at low speed idle. Thus the overheat alarm at idle.
Read here at this link http://forums.iboats.com/showthread.php?t=140345


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## Sequoiha

markw4321 said:


> Hurricane
> 
> I had a 150 yamaha 2 stroke that was only sounding an overheat alarm at idle. Replaced thermostats etc. just like you. Turned out to be the poppet valve which is a spring loaded valve that can get salt build up and freeze open which causes an overheat symptom at idle.
> What happens is the valve is stuck open and water dumps out before reaching the upper cylinders at low speed idle. Thus the overheat alarm at idle.
> Read here at this link http://forums.iboats.com/showthread.php?t=140345


 this is exactly right, i would have typed this but markw already did,, good call mark..


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## marmidor

markw4321 said:


> Hurricane
> 
> I had a 150 yamaha 2 stroke that was only sounding an overheat alarm at idle. Replaced thermostats etc. just like you. Turned out to be the poppet valve which is a spring loaded valve that can get salt build up and freeze open which causes an overheat symptom at idle.
> What happens is the valve is stuck open and water dumps out before reaching the upper cylinders at low speed idle. Thus the overheat alarm at idle.
> Read here at this link http://forums.iboats.com/showthread.php?t=140345


This is what I was thinking!


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## markw4321

How did it turn out?


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