Please Help: 7 Years of Buzzer Issues on 1996 Yamaha's 150's

[Doc of the Bay]

JB, 99, rod, and Central, thanks for all the troubleshooting tips. I am willing to try almost anything to fix this buzzer issue. The funny thing is that I can run a higher RPM, say over 4000 before it buzzes in calm water, but in rough water it seems to buzz at a lower RPM, say 3200-3600 RPM's. Sometime one engine, and occasionally both engines at the same time. This would lead me to believe that it is a short problem happening with the more vibration in rougher seas. But, the thermo switches all tested and closed between 190* and 194*, and I checked them when the buzzers go off and they were closed (light on with continuity tester, light off when the buzzer stopped) tells me it is somehow overheating. But, when I check the head temps right next to and also inside the cup where the thermo switches sit, it is reading no more than 140*. I used a infrared heat gun with a questionable accuracy, then a new digital meat thermometer, then I went and bought a digital ohm meter that has a temp probe and with all these temp tests, they were all at 140* or less with buzzer sounding. I was by myself in the boat, covers already removed, and when the buzzer sounded, I shut both down to idle and ran to the back and checked temps. I am sure I am having some cooldown from when it starts buzzing until the time I test the temp (about 30 seconds max). Thanks guys, Doc

[99yam40]

Doc,

Rodbolt17 is a Yamaha Master tech and knows his Yamaha motors, so listen to him and disconnect the connectors he said to ,if you can understand which ones.

I am just someone that just reads a lot and some times remembers some of what I have read in the past and can help others (Sometimes)

How did you test the switches with the continuity tester, and what kind of tester is this you were using?
Did you disconnect the switches completely from the rest of the wiring while testing?

Just for the heck of it, Did you ever look at oil levels on motor tanks when alarm went off?

[Doc of the Bay]

99, I used a needle type continuity tester (the type that looks like a pointed screwdriver with the clip on the wire and light in the handle). I bought a better one, not the elcheapo for a couple of bucks. Yes, I did disconnect the thermo switches completely for the test. The oil levels are always right below the top notch on the tanks on the side of the engine when the buzzer sounds. The red temp symbols blinks on the Yamaha management gauges when the buzzer sounds, never the oil light. I appreciate all the input, including Rodbolts expert advice. What I may try this weekend is to wedge my ohm meter temp probe between the rubber tip of the thermo switch and the block and this will record and store the temp readings from startup until it buzzes. Maybe this will show a spike in temp I am getting before I can run to the back of the boat and check the temps. Guys, if we can figure out my issue, you will all be the master mechanics in my book! Thanks, Doc

[Doc of the Bay]

Rodbolt, I will look for the bullet connector and do as you say. Please explain further what is the next step after disconnecting the gray wire bullet connector. Thanks, Doc

[99yam40]

Well so much for my theory about oil level.

How long have you owned this boat?
when were these motors installed on this boat?

Doc have you ever been able to run these motors at upper RPMs on this boat or any other?

[Doc of the Bay]

99, I bought the boat with motors (both '96 models) in 2002. No, I have never been able to get up to a higher RPM than around 4300 before the buzzer goes off. I did once as previously mentioned run at a higher RPM with I pulled all four thermo switches off of the heads and let them lay on the side of the blocks. Of course, no buzzer, no overheat on the gauges. I ran for probably 15-20 minutes with no issues and didn't burn them up! Doc

[99yam40]

2002 is more than 7 years ago.

So 4800 is the WOT RPM on both motors or is that just how hard you ran it?

Sure still sounds like overheat if dropping the switches keeps the alarm from coming in, but follow up on Rodbolt17's post

[CentralTexas]

There is no doubt I’m the least experienced here but I’m confused. Doc tested the temp sensors when going off AFTER DISCONNECTING THEM from the wiring harness and confirmed they were sounding a temp alarm. How can it be a downstream or cross ground issue? I realize Rod is an expert but I’m seriously confused.

Doc – am I correct that you are able to run over 4300 RPM but never have been able to without setting a temp alarm for as long as you’ve owned this boat?

This is some really good feedback guys.

[99yam40]

CT count me in on that too, you are not the only one that is confused.

I am thinking if Doc can record temp readings from inside pocket like he said, it should record temps that switches are seeing without any cooling off time between alarm and measuring.

almost positive the 2 switches on each motor are hooked up in parallel so only need one head on motor to hit the magic temp to alarm and on all motors one side is usually hotter than the other.
So make sure to measure/record at all switches.

I did have a OMC motor years ago that the wiring harness went bad and was leaking to ground and to other wires at the rubber plug connectors. took me a long time to figure that out

[Doc of the Bay]

99, I really don't know WOT, the buzzer beats me to it! 4800 I ran or close to it with the buzzers taken out of the heads. Central, that is correct. 4300 is about max RPM I have been able to run with the thermo switches installed before getting a buzzer. I will wedge my temp probe on my digital multimeter on each thermo switch cup one at a time and record the temps on each head from idle to buzzer and reply back. Thanks, guys. Hopefully I can run this temp test this weekend. Doc

[CentralTexas]

I have a question about trying to get an accurate measurement when the temp sensors go off and I’d like to learn a little more.

I understand it this way, which is probably wrong – The temp sensor connector is mounted in the head cover and the sensing part of it goes through the water passage between the head cover and head to the actual head itself. I’ve understood that they measure the head temperature directly rather than the water temperature between the head cover and head. It would seem to me that taking readings at the head cover may not correspond to what the actual head temperature is due to cooling by the water between the head cover and head as well as the cooling effect of the outside air on the head cover. If this is the case its dang near impossible to accurately measure the “head” temperature at the sensors point of contact.

What am I missing?

[99yam40]

if he can get the portable temp sensor into the same pocket or cup that the temperature switch that sets off the alarm resides in, then he should be able to see what the switch is seeing.
Yamaha designed these points of measurements to take readings, so I take it they are the best place to do the measurement.

We always used heat sink compound on the large electrical diode and SCR rectifier units (20,000 to 160,000 DC amps) where I worked to make sure the heat was transferred quickly to the cooling surfaces to protect the diodes and SCRs, but I do not think that is really needed for the temperature measurement of the motor itself. A few degrees off or seconds to get there should not matter.

I will try to post early in the morning before I make a run out into the bay, with the questions to rodbolt again as that has been pushed too far back in the thread and I would like him to see the questions

[jb123]

"The funny thing is that I can run a higher RPM, say over 4000 before it buzzes in calm water, but in rough water it seems to buzz at a lower RPM, say 3200-3600 RPM's."

= cavitation/water flow

[CentralTexas]

"The funny thing is that I can run a higher RPM, say over 4000 before it buzzes in calm water, but in rough water it seems to buzz at a lower RPM, say 3200-3600 RPM's."

= cavitation/water flow

JB - I probably don't have to say this but - you and I are in the same camp.

[99yam40]

Rodbolt17,
Are you saying to unplug both the white 4 wire connector and the grey wire bullet connector and leave them disconnected or just while troubleshooting for something taking it to ground?
Or is it just the grey bullet connector that needs to be disconnected?

Just trying to understand your instructions on post #27.

Moving this up so Rodbolt might get a chance to read it