Temp sender ohm readings

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   Looking for some help with my temp sensor readings. 1998 SN with GT40. Put in the lake first time this year and by the time I got to the dock my temp gauge was almost up to 240. Engine did not seem hot and the manifolds were cool to teh touch. Lake water temp is 62 deg. 
	I checked the temps with infrared thermometer and at the sensor on the water pump it was 160. Could find noreading over 160 anywheree. Troubleshhoting wiring and gauge etc. Found 0 ohms on wire from the gauge to the waterpump with both ends disconnected, so conetions there are good. cleaned up connections and temps readings came down but not acurate. 
	Took a couple of ohm reaidng on the sensor as the block coolde down. 
IR temp 156     120 ohms,    gauge reads 200
IR temp 125     196 ohms,    Gauge reads over 180<>

I did a couple hours of searching but cant find any chart that tells me what the sensor should read at what temp. Did find and old post the Pete mentioned the senders are 30-240 ohms and linear. Butnot starting point. 

Gauge drops to low temp with poer off and pegs to high 240+ when grounded.   Would more info on this before throwing parts at it. 

Thanks for any help you may have. 

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Mpost Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329	Post Options Post Reply Quote Mpost Report Post Thanks(0) Quote Reply Topic: Temp sender ohm readings Posted: May-14-2024 at 9:13am
	Looking for some help with my temp sensor readings. 1998 SN with GT40. Put in the lake first time this year and by the time I got to the dock my temp gauge was almost up to 240. Engine did not seem hot and the manifolds were cool to teh touch. Lake water temp is 62 deg. I checked the temps with infrared thermometer and at the sensor on the water pump it was 160. Could find noreading over 160 anywheree. Troubleshhoting wiring and gauge etc. Found 0 ohms on wire from the gauge to the waterpump with both ends disconnected, so conetions there are good. cleaned up connections and temps readings came down but not acurate. Took a couple of ohm reaidng on the sensor as the block coolde down. IR temp 156 120 ohms, gauge reads 200 IR temp 125 196 ohms, Gauge reads over 180<> I did a couple hours of searching but cant find any chart that tells me what the sensor should read at what temp. Did find and old post the Pete mentioned the senders are 30-240 ohms and linear. Butnot starting point. Gauge drops to low temp with poer off and pegs to high 240+ when grounded. Would more info on this before throwing parts at it. Thanks for any help you may have.
	84 SN Sold 98 SN Lund Pro V 1975 Alumacraft

KENO Members Profile Send Private Message Find Members Posts Add to Buddy List Grand Poobah Joined: June-06-2004 Location: United States Status: Offline Points: 11112	Post Options Post Reply Quote KENO Report Post Thanks(0) Quote Reply Posted: May-14-2024 at 5:42pm
	I suppose you know that the temperature is OK, otherwise you would have been coming home in Limp Mode. It looks like you might have changed the sender about 4 years ago. Here's the old thread in the link with some numbers that may or may not help. The link in that thread to Jamestown Distributors doesn't work anymore link I'd probably check for normal voltage going to the gauge positive connection and check all the connections clean and tight, but you've probably already done that. If the supply voltage is low, the reading is higher. An example of this is when somebody with wiring issues turns the running lights on at night and the temp gauge goes a lot higher., turn lights off and temp goes back down. The other gauges get affected too. it seems like your gauge itself isn't right, the ohm readings were about like what I got below I took some readings on an engine and at 120 by IR gun the sender was 240 ohms 125 degrees was about 200 ohms........you had 196 ohms at 125 degrees by IR gun At 130 degrees it was 185 ohms At 140 degrees it was 175 ohms That's all I could get cause the engine didn't get any hotter

Mpost Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329	Post Options Post Reply Quote Mpost Report Post Thanks(0) Quote Reply Posted: May-15-2024 at 9:20am
	After posting this thread I did find my old post. At that time I did not replace the sender, as the one I orrdered was the qring thread size, After my above testing I cleaned up all connections on the gauge and put back together but did not run the engine again. We went for a spin yesterday afternoon and gauge is now reading as it was in the past at 175 to 180 with the 160- degreee thermostat. IR readings at sender were at 160-165 I will do some testing on the voltages at the gauges and see where those are at. i have done this inhte past nad all was well, buthtat was a few years ago. I also ordered a new sender and some resistors to do some testing of the gauge itself. Will see what this gets me.
	84 SN Sold 98 SN Lund Pro V 1975 Alumacraft

Temp sender ohm readings

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