Temp Sensor - knowing when it's bad?

[scarpint]

Was watching my temp gauge while running my motor in the driveway and noted it went from 145 degrees all the way to the left. It hasn't moved since. Saw a great tip here and removed the wire at thermostat housing and touched ground and temp gauge needle moved all the way to right. Did this once. Removed sensor/sending unit fom housing and cleaned it up. Appears to be all brass. Reinstalled and nothing.

So, my question is, do these units go bad? I did not clean up threads inside of housing.

Thanks for considering.

 

[Oshkosh1]

Re: Temp Sensor - knowing when it's bad?

Yes they will go bad. You can test for resistance. It should read somewhere between 30-250 ohms starting HIGH (240-250ohms) and decreasing as the temp rises.

 

[spdracr39]

Re: Temp Sensor - knowing when it's bad?

And make sure your thermostat housing is properly grounded. If someone changed the thermostat and didn't use a mercruiser gasket it could be losing ground. jump a ground wire from the housing to the engine somewhere and see if it starts reading accurately.

 

[scarpint]

Re: Temp Sensor - knowing when it's bad?

I replaced the thermostat a couple of weeks ago and used Quicksilver OEM parts. Temp gauge had been working since I did this. Will check resistance.

 

[04fxdwgi]

Re: Temp Sensor - knowing when it's bad?

I replaced the thermostat a couple of weeks ago and used Quicksilver OEM parts. Temp gauge had been working since I did this. Will check resistance.

Did the housing base gasket have the 4 little brass rivets in it? If not, then the housing may not have a good ground to the intake manifold. Oh yeah, sure you've heard this before, but do not use teflon tape on the sender threads, as it will insulate the sender from ground.

 

[scarpint]

Re: Temp Sensor - knowing when it's bad?

Thanks for the answers. Good stuff. One question on the ground. Wouldn't the mounting bolts for the housing provide a good ground?

 

[04fxdwgi]

Re: Temp Sensor - knowing when it's bad?

Thanks for the answers. Good stuff. One question on the ground. Wouldn't the mounting bolts for the housing provide a good ground?

Not always. The top plate is insulated from the body by a gasket too, so maybe yes, maybe no. Hence the rivets on the bottom gasket ((or run a seperate ground wire to a stud drilled / installed on the body (not on the water jacket part), like I did, to eliminate any questions)).

 

[series60]

Re: Temp Sensor - knowing when it's bad?

Wouldn't the mounting bolts for the housing provide a good ground?

I have wondered about that also. There must be a reason to ground the housing just haven't heard an answer.