Sensor On Engine

[boatmon345]

Post-rebuild of a 1997 Yamaha 150HP Salt Water Series II S150TXRV 2 stroke 6 cylinder powerhead.<br />( Click here to view updated blog with new pictures )<br /><br />Can someone tell me what kind of sensor this is? I believe it is a thermosensor but it is not testing correctly like a thermosensor should, according to the book:<br /><br />

 

[rodbolt]

Re: Sensor On Engine

looks like the thermosensor to me. what tests are ya running and what is it not doing?

 

[boatmon345]

Re: Sensor On Engine

Book advised to measure using a pot of water on a burner, and a thermometer & ohmmeter. I did that and recorded these measurements:<br />Temp(F)...Resistance(ohms)<br />81........45,700<br />93........37,000<br />110.......25,300<br />140.......13,200<br />180.......6,250<br />209.......3,455<br />(with many more data samples in-between)<br /><br />Book indicates "Thermoswitch Resistance Specs":<br />41F 12000ohms<br />68F 5400-6900ohms<br />212F 3120-3480ohms<br /><br />It looks like the 212F spec shows that my sensor works properly at that temp. But, below that temp the resistance is way higher than it should be.

 

[rodbolt]

Re: Sensor On Engine

at 68* it should have about61.6Kohms and at 212 it should be about 3.3 Kohms.<br /> your numbers look close. the tolerance is 20%. does the engine start and idle fast for a few seconds then settle down to normal idle? thats what that sensor controls. it controls idle timing at start up and warm up.<br /> the thermosensor is strictly for aid in warmup on that model, the thermoswitch's control the audible and RPM reduction functions.

 

[boatmon345]

Re: Sensor On Engine

Thank you Rodbolt. I can't say that the engine runs fast at start then settles down, but I will keep a close eye on it. I will install the sensor back on the eng. Book must be errant in this case.<br /><br />Thanks.

 

[Silvertip]

Re: Sensor On Engine

The problem with using a thermometer and ohmeter in water testing is that the thermometer and thermister don't track exactly. In other words one or the other may react to changing water temp much faster or slower than the other. Currents set up in the water as it heats will make if important where you position the thermometer. I use a wood strip with a slightly undersize hole in it to precisely position the thermomenter (remember it cannot contact the bottom of the pan). The sensor is also positioned as near the thermometer tip without touching. I'll bet if you ran the test several times you'll find differing readings. Your sensor is probably ok. Devices like these typically (and very roughly) have a 10:1 ratio from below ambient to 212 degrees.

 

[boatmon345]

Re: Sensor On Engine

OK thanks for those tips Smoke. I understand what you are saying about the currents. I stirred the water with a spoon and kept the tip of the thermometer about an inch from the sensor, but the tracking very well could have been different. I plan to reinstall this sensor tonight. Thanks again..