The motor is a 2004 Yamaha Vmax 150HP carbed 2-stroke. Had it for 3 years, no issues until this. Last full trip was summer 2014, ran fines.

Then, a few weeks after my last full lake trip, around September 2014, I put on the muffs to run water through the system and start and run for a few minutes, and the overheat alarm sounded (constant, steady buzzing sound). It came on after about 4-5 minutes of running time. At that time, I noticed it had no pea stream [*I'm using the word "pea" because the forum blanks out the other word]. Of course I immediately shut off the motor after the alarm came on. So I assumed the engine needed an impeller replacement [I have not had the impeller/water pump replaced since I purchased the boat about 3 years ago].

Well, I got very busy these past few months and only got around the trying to replace the impeller yesterday 4-25-15 [I know, it had been several months since I even tried starting the engine and it just sat there.] So I had already bought the replacement impeller a couple of months ago and yesterday, I went to replace it. I took the lower unit off, removed the water pump housing and the old impeller was actually in fairly good shape; I did not see any scuff or damage marks whatsoever. I was surprised at how clean looking it was. Also, the water pump housing, seals, shaft, etc. looked very clean and no damage or scrape marks whatsoever along the inside of the metal cup that encloses the impeller. There was a little bit of sand in the cup, which I cleaned out. So I replaced with the new impeller and tried again.

Same problem----the engine started up just fine, and there was a decent pea stream [I would say, from what I recall, that the stream is slightly weaker than I have seen it in the past, but there was definitely a decent pea stream]. But the overheat alarm came on just 3-4 minutes after start up. Of course, I immediately shut it off to prevent any engine damage.

I tried again this morning. This time, I got a large container which I installed up underneath the lower unit, filled it up completely with water [the water level in the container reached up past the intake openings, so it definitely had good water.] I tried starting again, but this time it was strange----I had absolutely no pea stream at all [but I did notice a slight bit of steam coming from the pea stream outlet], and after about 4-5 minutes, the overheat alarm came on. I immediately shut off the engine.

What would cause an overheat when the engine has water flow stream and also when it has no water flow stream? [Also, why would the alarm sound like clockwork, i.e. about 4-5 minutes after the engine has started running and idling?] I think I've eliminated as a possible cause the water pump/impeller since the old one looked fine and it has a brand new one now.

Any thoughts?

Either the thermostats are stuck closed,or the pressure relief valve (poppet valve) is stuck open,which would return all or most of the water back out the bottom before it could reach the top of the motor,where the pea hole is.Probably the latter,cause if the Tstats were stuck closed,you should still get a decent pea stream. Search "poppet valve" in this topic,and you'll see where I,and others here,have had this issue. I actually have a new poppet valve conversion kit still in the package here,waiting for me to get one those ( how you say) Round "tuit" things.

You need water up above the cavitation plate for running in a tub. Poppet dirty

Oh ok. I will research the poppet valve, and report back. Thanks for the quick response, guys.

Ditto

What does it do in a lake? What others have said still applies for checking, but running on muffs will trigger the overheat alarm if you run it very long. My 200 will throw the overheat alarm on muffs. As good measure I replaced the poppet valve with the new design and thermostats because I had no idea when they have been touched last. It will still throw the overheat alarm if I run it on muffs for a bit, but it does completely fine in the lake.

Ordered the poppet valve and thermostats for swapping. Waiting for them to shipped. I might stop by and pick up some new muffs, just in case that might contribute to the problem.

Joe, I haven't had it in the lake for about a year; the problem started on the muffs and has been ever since. Prior to this, I never had an overheat alarm with this motor at all.

Will report back.

Get the dual inlet with square pads. The round pads will not seal the bottom of the water intake.

Got it. Will do, Gary.

I've seen the poppets get stuck open by a small piece of gravel that will not let it close all the way several times. could be something stuck in there not letting the poppet close.

I will definitely check both the existing poppet valve, thermostats and look for any clogging/debris when I go to swap them out. Will try to take pics, also. But won't be able to get it done until this weekend. Will report back then.

pea stream on my pro V quit, took an air hose and blew it out, works fine.

Alright, I picked up working on the boat this weekend.

As I said earlier, we changed the old impeller a couple of weeks ago. Here is a picture of the old impeller. You can see the old one was in near perfect condition, despite not having been changed in at least 3 years or so. No noticeable scratches, tears, shreds, debris, etc. Regardless, I went ahead and swapped this one out for the new one I ordered:



Also, as indicated earlier, I ordered two new thermostats and a poppet valve and spring for replacement. This is what I did this weekend. So I started by removing the port side thermostat and housing:



As you can see, there really was not much junk or debris around this thermostat. When I pulled out the old thermostat, it wasn't in too bad a shape. So, I ruled out any possible clogging for this thermostat as a problem.

Then I did the same thing for the starboard side thermostat housing:



Again, it wasn't too dirty. There was minor stuff caked in and around the housing and thermostat, but nothing substantial. Even the gaskets for both thermostat housings were in near perfect shape. After removing both of these housings, I cleaned them up really good, brushed away any caked-up debris, and installed the new thermostats. Also, for good measure, I did test the old thermostats for proper function by placing them into a pan of boiling water and they both worked fine and "springed out" once the water got to a certain temperature [one of them was a bit slower to open than the other, but I did not think this was too important since I would be changed them anyways; and obviously, I tested the new thermostats out of the packaging to ensure proper function and they worked fine.]

The next thing I did was tackle the poppet valve. I removed the housing, spring and valve and found 3 baby-size pebbles that could have been causing problems (or so I was hoping). I cleaned these out and brushed and sprayed as best I could. Also removed the old spring and vale and replaced with the new "mushroom" style valve and ensured it fit properly:



***I did not change this rubber ring grommet inside the poppet valve housing you see above. It appeared to be in good condition from the outside view. Also, I did not order this when I ordered the poppet valve and spring. If I need to do so, let me know.





After changing the new thermostats and poppet valve, I flushed the motor. I used a water hose, hooked it up the tube on the port-side of the motor for flushing, and flushed the system (not running) for approximately 10 minutes. All seemed to be well, as the [censored] stream was solid and all other orifices for releasing water seemed to be spitting out water as normal.

Then I tested for the overheat alarm. And to my surprise, it came on again. I started the engine, ran for approximately 4-5 minutes, and the constant buzzer sounded. I immediately shut it off.

Help, please.

Have you checked for a blockage where the stream exits the motor, I've had that get blocked a few times but it was on a mercury, I've never owned a Yamaha so I'm just throwing out a suggestion.

Brian, if you are talking about the pea stream hole from the starboard side of the motor [I think it's called the telltale??], yes I checked that and the black hose leading into it for blockage. Blew it out with air compressor. It was fine.