How to check temperature switch

[D0T-C0M]

On my 1995 130HP johnson OB the temperature switch on the heads was disconnected by the previous owner because it was making the engine cut out falsely. When I bought it the previous told me he had brought it to the dealer and they told him the switch was faulty and ordered a new one. The business subsequently went into bankruptcy and he never had it installed.

I have the sensor in hand and I would like to test it to see if for sure its faulty before buying one. Is there a way to test it ?

 

[cfauvel]

Re: How to check temperature switch

Sure....get an ohm meter between the two leads when cold...it should be infinite , alternatively a sounding continuity setting on meter. when cold no sound/no continuity. Then stick the swith into boiling water, at above 175 or so the switch should close...definitely by 220 boiling point, the swithc should close.

 

[D0T-C0M]

Re: How to check temperature switch

@cfauvel thanks

Does the service manual state what the switch is supposed to activate at? I did a check in a calibrated furnace and the switch operates at 115c/230f. I also did a insulation test of the switch and there is 50Mohm resistance between the sensor case and both wires. This would seem to be a good sensor. I don't want to install a $100 sensor if the sensor is good.

 

[D0T-C0M]

Re: How to check temperature switch

Also the complaint was that the engine would cut out or sputter and when the sensor was disconnected the engine ran correctly. I am beginning to suspect maybe the wiring.

 

[cfauvel]

Re: How to check temperature switch

@cfauvel thanks

Does the service manual state what the switch is supposed to activate at? I did a check in a calibrated furnace and the switch operates at 115c/230f. I also did a insulation test of the switch and there is 50Mohm resistance between the sensor case and both wires. This would seem to be a good sensor. I don't want to install a $100 sensor if the sensor is good.

The manual should state when the switch should close the circuit. I wouldn't place the switch over a flame, rather place in a pot of water.

 

[cfauvel]

Re: How to check temperature switch

Also the complaint was that the engine would cut out or sputter and when the sensor was disconnected the engine ran correctly. I am beginning to suspect maybe the wiring.

Can't answer that question, but sounds logical. On my '86 V6 the engine would sound a horn if overheating...if you short circuit the temp sensor does the horn sound?

 

[D0T-C0M]

Re: How to check temperature switch

I didnt put it over an open flame, I used a digital calibration furnace that we use at work for calibrating temperature gauges on large industrial transformers. No open flame never.

 

[D0T-C0M]

Re: How to check temperature switch

What is the sensor on the stern side that has one wire? Is it a switch to ground? Anyone have a electrical schematic they could send me?