temp sensor question

Old Yeller Boater

Petty Officer 2nd Class
Joined
May 17, 2010
Messages
191
I checked my sensor with a multimeter. With engine running, the number started over 2.0 but gradually dropped to about 1.3 as the motor warmed up. When checking, I put one lead on the end of the sensor, and the other lead grounded to the block. Should I have checked it with the lead on the base of the sensor instead? When I tried that my reading was 1.0 and didn't register over 2.0 until I put the lead on the block to ground.

thx......
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,093
Re: temp sensor question

Just what are we checking for.should be reading resistance
 

Old Yeller Boater

Petty Officer 2nd Class
Joined
May 17, 2010
Messages
191
Re: temp sensor question

yes....my readings above are with meter set to ohms. While researching, I read in another post (which I can't find) that the readings should be above 2 and come down as the motor heats up. That seems to be the case as long as the ground lead is touching the block. I just want to confirm I should have the ground on the block and not on the base/nut on the temp sensor.

Assuming I've checked it properly, it would appear that my problem would be at the gauge.
 

wellcraft-classic210

Master Chief Petty Officer
Joined
Sep 22, 2010
Messages
839
Re: temp sensor question

Old Yeller

You may want to read this post ;

http://forums.iboats.com/showthread.php?t=539040&p=3690539#post3690539


Also
If you ground the wire going from your gauge to the sending unit WITH POWER ON does your gauge should go to its highest temp. If you disconnect the wire from evwerything does it go low. That verifies the gauge & related wiring circuits.

The temp sending unit is a variable resistor. The range of resistance in ohms THROUGH IT should be much higher than several ohms. Its imperative that the wire to the gauge is removed for this test / It should read more like this.

A functioning sender has a resistance of between 600 to 800 ohms at 70 degrees Fahrenheit and 55 ohms at 212 degrees Fahrenheit.

Read more: How to Test a Water Temperature Gauge on a Boat | eHow.com http://www.ehow.com/how_7949115_test-water-temperature-gauge-boat.html#ixzz1z0odpzry. ( I will try to come back with the spec )
The body of the sender needs to grounded to complete the ciciut and that should be less than to ohms to a known good ground such as the engine bloack and or battery.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: temp sensor question

I checked my sensor with a multimeter. With engine running, the number started over 2.0 but gradually dropped to about 1.3 as the motor warmed up.

You can't measure ohms with power on the system. Ohms never checked with power on the system.

ohms test.jpg
 

Old Yeller Boater

Petty Officer 2nd Class
Joined
May 17, 2010
Messages
191
Re: temp sensor question 3.7 Mercruiser

Re: temp sensor question 3.7 Mercruiser

I determined that the temperature sender needs to be replaced. Picture attached shows serial number 93300184. I want to be sure I get the correct sender. Mercruiser parts sites show one for about 65-70 bucks, but I found a link to this site. I believe the 1/2 inch x 14 thread would be the correct one. Could anyone confirm this?

http://www.psepmarineparts.biz/store/mercruiser_water_temperature_senders.htm
 

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