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Old 11-25-2020, 09:44 PM   #1
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Default Temp Sending Unit Question

The FSM for my 95 Hardbody KA24E says that the resistance at 100 degree Celsius for the temp sending unit should be 21-24 Ohms.

My sending unit along with three others that I picked from the junk yard all read around 50 ohms at that temp. Could the FSM be wrong or are all four sending units defective? It's hard to believe that all four sending units read the same resistance at 100 degrees C and have twice as much resistance as the FSM says they should have at that temp...

Interestingly, my temp gauge reads about half of where it should read, which is about half on the gauge. Mine reads at 1/4 at full temp...

if anybody is super cool and would be willing to perform the same test that I did (heat your sending unit up to 100C and tell me what resistance you get) I would be forever grateful.

Its also weird that the brand new OEM sending unit that I ordered, making sure I have the correct part number that all Nissan websites say I should have (25080-89903), reads about 150 ohms at 100C. I put it in my truck and the needle barley moved at full temp. What gives?
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Old 11-25-2020, 11:29 PM   #2
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It will read lower by 50% if it has 2x the resistance because a short is max hot. As resistance climbs the gauge will go down.
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Old 11-26-2020, 12:22 AM   #3
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Originally Posted by Deerhurst View Post
It will read lower by 50% if it has 2x the resistance because a short is max hot. As resistance climbs the gauge will go down.
Yes sir, I figured that out. I just don't get why all four sending units that I have, read the same- twice the resistance that the FSM says they should have at 100C. What are the odds that all four are bad? Is the FSM wrong you think? Also, its weird that the "correct" part number that all Nissan part suppliers are giving me is reading at three times the correct resistance according to the FSM at 100C. Im stumped
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Old 11-26-2020, 12:38 AM   #4
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All for may not be "bad" but cheap resistors (it is not a thermocouple) do wear and have value change over time. It's due to the TC of the part. I do resistors for a living.





I wonder if the new ones are different value due to a change in later years. Probably the same part used in many engines.



What motor? What brand sensors?
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Old 11-26-2020, 12:57 AM   #5
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Deerhurst thanks for taking the time to hear me out! The part number that all Nissan sites tell me to order is 25080-89903. It arrived in a little Nissan baggie and was shiny and new. The odd thing is that the prong in which the plug sits is shaped a little different than the 4 original sensors as well as it's 2mm bigger in socket size... The original sensors are 10mm and the new one is 12mm... Those two differences along with the resistance being three times higher than the FSM says it should be at 100C makes me think that it is the wrong part. But why would all websites say its the right part? The seller of the part is kind enough to send me another one to see if the new one he sent me was defective. I'll be getting that one in a few days, but I have a hunch that it will give me the same readings as the first one he sent. Thanks again for the help sir!
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Old 11-26-2020, 02:47 AM   #6
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Makes me wonder if the part number is i correct/and updated part.
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Old 11-26-2020, 06:17 PM   #7
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Quote:
Originally Posted by Deerhurst View Post
Makes me wonder if the part number is i correct/and updated part.
Totally! I'll report back on the resistance reading of the new sending unit when I get it in a few days. If anyone has any info on this particular conundrum, I'd love to hear it!
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Old 11-28-2020, 06:19 PM   #8
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Nissan used that same sensor back in the 80's, on multiple vehicles...
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Old 11-28-2020, 08:13 PM   #9
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Originally Posted by YEPEE View Post
Nissan used that same sensor back in the 80's, on multiple vehicles...
Yepee can you tell me if this is the correct sensor for my 95 KA24E? It seems that it isn't unless I'm missing something... The FSM says that it should have 21-24 ohms of resistance at 212 degrees Fahrenheit, but after testing two brand new ones, they read about three times that resistance. When installed in my truck, the temp needle only moves a hair at full temp. I'm really stumped here.
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Old 11-28-2020, 08:15 PM   #10
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Quote:
Originally Posted by Deerhurst View Post
Makes me wonder if the part number is i correct/and updated part.
So I tested the new sensor that I received and it reads the same- about three times the resistance that the FSM says it should at 100C. I hear you are an electrical expert, so any thoughts or advice would be greatly appreciated. Thanks!
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