Temp Problem

Troops141

Cadet
Joined
Apr 30, 2015
Messages
7
I have a 1993 Caravelle with the Mercruiser 3.0 LX. Last year was the first year that I had it and noticed that the temp gauge did not work. I finally dug into it today since I am getting ready to use it again. The boat is used in MN so it is freshwater only and does not sit in the water when not in use.

I have been reading quite a bit about this issue and tested the gauge by grounding out the tan wire at the sender. The temp gauge spiked all the way to the right, so I know the gauge and wiring from the sender to gauge is good.

This is where I have read conflicting statements and hoping that you guys can help me.. I took out the sender and started to check the resistance. At room temp, it had 780 Ohms. I then nuked some water and put it in there to see how the Ohms changed. At 170 Degrees F, it had 100 Ohms, at 160 Degrees F, it had 125 Ohms, and at 140 Degrees, it had 215 Ohms... I have read that this is normal operation and then I have also read that the large jump between 160 and 140 Degrees would indicate a bad sender...

Can you guys tell me if this is normal?? If it is normal, I'm guessing the issue would be the thermostat, if so, do you guys know what temp thermostat I'd need??


Thanks for helping.
 

alldodge

Moderator
Staff member
Joined
Mar 8, 2009
Messages
42,358
I have a 1993 Caravelle with the Mercruiser 3.0 LX. Last year was the first year that I had it and noticed that the temp gauge did not work. I finally dug into it today since I am getting ready to use it again. The boat is used in MN so it is freshwater only and does not sit in the water when not in use.

I have been reading quite a bit about this issue and tested the gauge by grounding out the tan wire at the sender. The temp gauge spiked all the way to the right, so I know the gauge and wiring from the sender to gauge is good.

This is where I have read conflicting statements and hoping that you guys can help me.. I took out the sender and started to check the resistance. At room temp, it had 780 Ohms. I then nuked some water and put it in there to see how the Ohms changed. At 170 Degrees F, it had 100 Ohms, at 160 Degrees F, it had 125 Ohms, and at 140 Degrees, it had 215 Ohms... I have read that this is normal operation and then I have also read that the large jump between 160 and 140 Degrees would indicate a bad sender...

Can you guys tell me if this is normal?? If it is normal, I'm guessing the issue would be the thermostat, if so, do you guys know what temp thermostat I'd need??


Thanks for helping.

:welcome: to iboats

Here are the readings for normal operation
Water Temperature Ohms Reading
140? F (60? C) 121-147
194? F (90? C) 47-55
212? F (100? C) 36-41
 
Last edited:

Troops141

Cadet
Joined
Apr 30, 2015
Messages
7
:welcome: to iboats

Here are the readings for normal operation
Water Temperature Ohms Reading
140? F (60? C) 121-147
194? F (90? C) 47-55
212? F (100? C) 36-41

Thanks for the welcome, and it looks like the 215 Ohms @ 140 degrees is way to much and would indicate a bad sender.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,001
Ayuh,.... Welcome Aboard,.... Ya mighta found yer problem,.....

Another point, when the T-stat is changed, ya gotta use the marine gaskets, which have little brass rivets to insure continuity to the block, to ground, so's the sender can work,....

Test the ground at the T-stat housin',...
 
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