1990 Pro V 150 Alarm at Idle...Need some help

I have a 1990 Pro V 150 and I have been having issues with the motor going into alarm when at Idle. I Purchased this at the end of last year and it ran great. I never had this issue, but I never let it idle for an extended period of time either. It goes into alarm if it idles for around five minutes. I then shut it off and let it cool and it will run fine until it idles too long again (takes around 10-15 minutes for alarm to stop). Otherwise it runs good under load and idles smooth.

I have done all the simple fixes that have been suggested on this forum.

- Water Pump - Full replacement
- Thermostats
- PRV valve: this I didn't change but cleaned and reinstalled, was in good shape.

What I found in doing all of this was that this motor had overheated at one time.

- The water pump had been changed and I found some melting in the plastic housing, nothing major, but it obviously had gotten hot once. I changed this first thinking it would fix the issue, but it didn't

- Next I addressed the PRV, the local parts store didn't have the new mushroom PRV so I took it out and cleaned it. I found a pebble of sand between the valve and the grommet. To be honest it didn't look stuck open. I cleaned it all and reinstalled it with a new gasket. I also changed the thermostats at this time, dropped the lower unit again and flushed water from a hose down from the stat housings to clean out any gunk that may be causing the issue. Sadly after all that I got the alarm again.

Today I noticed that it was the #1 cylinder (Top left as looking at the motor) that got hot. The temp sensor shows signs of getting too hot. The grease got cooked around it and the jacket on the wires is visibly heat damaged right as the enter the sensor, but I doubt the conductors inside got that damaged.

Would a bad sensor be causing my issues or did some serious damage take place and my motor is not cooling properly and causing the alarm?

The Bat signal out for a Yamaha Guru!!!

Re: 1990 Pro V 150 Alarm at Idle...Need some help

You can pull and test the temp sensors in a pot of water measuring the temp as you heat it and monitor the operation to see if they work in spec.

More than likely you have some blockage in cooling passages if you are sure the PRV is not sticking open, but then it would tend to overheat at higher RPM. Kind of at a loss at this point also

Re: 1990 Pro V 150 Alarm at Idle...Need some help

I picked up some new heat sensors and performed a compression test.

Results for the compression test were 90psi on all cylinders. Is this low, and if so how low?

I ran the motor on the muffs to try and see if the sensors were the issue and I still got the alarm, when I disconnected the sensors the alarm stopped so I think the motor actually is getting hot.

One thing I noticed when running on the muffs was that the motor was not peeing out of the tell tell, It was drawing water up as plenty of water was flowing out of the various weep holes in the lower unit. Again this is a new water pump, impeller, housing, ect. I did the full kit replacement. The motor does pee just fine when in the water, but it didn't on the muffs. I think this means something

Is there a way to flush the system if I have some kind of blockage? Obviously I have a circulation problem at idle when the motor is not under load.

This is a fresh water motor as well.

Suggestions?