1991 150 tlrp pro v

[Ray Ritchotte]

Couldn't find my old post on my overheat problem. I think my mechanic and I found the problem. Went on the lake today and my mech. brought his thermal heat gun and at 3ooo rpms the engine temp was 115 degrees. Advanced the throttle to 4300 and 2 minutes later the O'heat light and horn sounded. Took a reading and both heads are at 140 degrees. Let it cool down and started over and when the O'heat alarm sounded we took another reading and still 140. puled the wires on the port senser and horn quit and light went out.
Water press is 25 psi constant. My mech. says to order the senser and I need a part #. Do you think this was my problem all along ???
Every where on the engine the temp never went over 140 degrees.

[rodbolt17]

wont be the first thermo-switch ever failed.
it can be ordered here or any yamaha dealership.
myself, I would remove and test the switch before randomly replacing it.
a hot spot under the head will do that as well.
dont see much of that on freshwater stuff but it can happen.

[Ray Ritchotte]

Overheat

wont be the first thermo-switch ever failed.
it can be ordered here or any yamaha dealership.
myself, I would remove and test the switch before randomly replacing it.
a hot spot under the head will do that as well.
dont see much of that on freshwater stuff but it can happen.

Thanks Rod bolt.
We pulled the thermo switch from the head and used the thermo heat gun on the hole that the thermoswitch sits in and it read 140 degrees,

[Ray Ritchotte]

150 tlrp 1991

Thanks for the info Rodbolt. We pulled that senser from the head and pointed the lazer heat gun on the hole the senser sits in and it read 140 degrees. I couldn't believe how easy it was to come out. DO you have a part number and does it come with a new rubber grommet or do I have to order it seperately ??
Would you also suggest installing a mechanical temperature gauge and sending unit in the starboard head where the plug is on top of the head or just rely on a light and a warning horn ??

[99yam40]

click on the purchase Yamaha parts at the top of the page and look up you motor and parts or this link
Yamaha Outboard Parts

[Tucker]

Is there a way of testing the part without comparing temps with a heat gun. I bet the Yam tech was loving you. How many hours does the guy have into diagnosing the problem? That's why I like working with the old guys. They've probably seen this problem, where as the young guy is charging you for his learning curve.

[99yam40]

the manuals say tp put into a pot of water with a thermometer and heat while hooked to a ohm meter to see what temp it changes

[Ray Ritchotte]

Is there a way of testing the part without comparing temps with a heat gun. I bet the Yam tech was loving you. How many hours does the guy have into diagnosing the problem? That's why I like working with the old guys. They've probably seen this problem, where as the young guy is charging you for his learning curve.

Actually my tech did not charge me. I have known him for a long time.
He even would not take any money when he went to the lake with me.
The heat gun never went over the 140 degree mark even when the horn and light came on. He actually helped me a lot trying to diagnose my problem.
The lake trip was his idea and he even drove there in his personel truck on his day off.
This heat thermal gun is very accurate and he uses it a lot when he runs the motors in his tank. We just couldn't test my motor in the tank so he met me at the lake.

[Ray Ritchotte]

the manuals say tp put into a pot of water with a thermometer and heat while hooked to a ohm meter to see what temp it changes

Okay,
I hate to be a pest but I am learning more than I ever did on this forum.
I pulled the senser and I did as you said. I boiled water in a pan using an A/C
mechanic heat thermometer and all three times the OHM's meter read ohms at 140-145 degrees. I believe that this senser should not come on until it reaches 180 degrees.
Feel free to jump in and give me more info.
I have learned more in the past 6 months about my motor than I thought I would ever learn. You guys are great.
Ray

[99yam40]

My C40TLRX has 2 switches one closes at around 100-120 to tell the CDI that the motor is warmed up and the other closes at around 200 to say it is overheated.
What does your service manual say yours is suppose to operate?

This is why it is necessary to have a service/ repair manual for your motor, to look up the specs and it gives step by step instructions for testing all the different systems and parts.

[Tucker]

If the motor is carbed what does the CDI do when the first switch closes at 100?

[99yam40]

readjusts the timing back to the normal idle timing.