 Oil Temp Indicator = Oil Temp Sender/Sensor? |
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| torakki |
 Aug 24 2025, 05:25 PM
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#1
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Member  Group: Members Posts: 66 Joined: 5-October 18 From: Nor Cal Member No.: 22,545 Region Association: Northern California  |
I'm trying to track down a temperature issue on our 2.0L, and have replaced the gauge and sender. Temp still goes to red (about 280F), within 10 minutes of driving. Temp is actually around 165F from a laser temp reader. Only thing I can think of is wiring.
Am I correct, when I see the wiring diagram showing the Oil temp indicator is the same as the sensor? The diagram shows an "indicator" and a "gauge". I want to run some external, new wires to see if there's a difference. Thanks for any knowledge.  |
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Replies(1 - 11)
| 930cabman |
Aug 24 2025, 05:50 PM
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#2
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Advanced Member Group: Members Posts: 4,233 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States 
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(IMG:style_emoticons/default/headbang.gif)
seems very odd, wish I could be of assistance, but I have never ran across this. I use a laser temp sensor often and found them more or less accurate |
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| dtmehall |
Aug 24 2025, 05:55 PM
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#3
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Member Group: Members Posts: 142 Joined: 21-December 23 From: Farmington Hills, Michigan Member No.: 27,808 Region Association: Upper MidWest |
Assuming that you have the correct wiring diagram from your model year.
I would agree that the 'indicator' legend means the temp sensor |
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| JeffBowlsby |
Aug 24 2025, 06:55 PM
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#4
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914 Wiring Harnesses & Beekeeper Group: Members Posts: 9,024 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None
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Please state the model year of your chassis.
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| Dave_Darling |
Aug 24 2025, 08:37 PM
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#5
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914 Idiot Group: Members Posts: 15,236 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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What are you getting the temperature of with the laser? Just the metal on the outside will certainly be colder than the oil on the inside...
--DD |
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| torakki |
Aug 24 2025, 08:44 PM
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#6
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Member Group: Members Posts: 66 Joined: 5-October 18 From: Nor Cal Member No.: 22,545 Region Association: Northern California |
The car is a 1974 2.0L. I was pointing the laser at the cases just above the bottom fin area. I also wasn't sure how fast the inside temp of the oil would conduct to the outside of the cases. But, comparing a 10-minute drive to a 30-minute drive, laser temps were the same.
Also, the wiring diagram is stated as a 1974. I believe it's on this site. I will run new wire from the sensor to the gauge and a new ground wire from the gauge to a new ground. Thanks for the feedback. |
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| JeffBowlsby |
Aug 24 2025, 09:14 PM
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#7
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914 Wiring Harnesses & Beekeeper Group: Members Posts: 9,024 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None
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Your posted circuitry is accurate, but it’s not the 74 chassis harness schematic. This circuit is the same on the 73-76 cars.
74 schematic is here: https://bowlsby.net/914/WiringHarnesses/doc...4_MAIN_1974.pdf |
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| bdstone914 |
Aug 25 2025, 01:51 AM
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#8
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bdstone914 Group: Members Posts: 5,089 Joined: 8-November 03 From: Riverside CA Member No.: 1,319 |
Get a laser temp from the oil filter or sump plate. Another way to verify if you are really around 280 is squirt water on the oil filter. It should turn to steam. You may have the wrong sender for the gauge.
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| TRP |
Aug 25 2025, 06:01 PM
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#9
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Newbie Group: Members Posts: 32 Joined: 2-September 23 From: Morgan Hill, CA Member No.: 27,559 Region Association: None |
I was thinking the same thing that @bdstone914 noted, are you sure you have the right gauge/sending unit combo? I once had a set of 356 gauges in a speedster that read all wonky due to mismatched senders to the gauges.
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| torakki |
Aug 25 2025, 07:41 PM
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#10
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Member Group: Members Posts: 66 Joined: 5-October 18 From: Nor Cal Member No.: 22,545 Region Association: Northern California |
Looks like the new schematic from Jeff match's what I'm seeing in the car. And the sensor is a 200C which is what the original was that should match the gauge which matches the '74 car. I started stringing some wire and connectors together so if it's not too hot tomorrow, I'll play car tetras, get it in the garage and run some new wire. That's a good idea about getting the reading off the filter. Thinner metal should heat up quicker. I'll post updates when I finally get it tested. Here's the readings and it was about 2 minutes after shutting the engine off.
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| bdstone914 |
Aug 25 2025, 08:24 PM
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#11
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bdstone914 Group: Members Posts: 5,089 Joined: 8-November 03 From: Riverside CA Member No.: 1,319 |
The sensor reads resistance to ground. You may have a short to ground on the sensor wire. I would pull the gauge and hook it up in the engine compartment. The green with stripe sensor wire have a union on the passenger side of the engine compartment. Hook up the gauge there with some jumper wires. If you get the same false hot reading the sensor wire may have worn insulation and shorting to ground. If so string a new one. The original path is in back of the fan shroud.
You would need to drop the engine to use the same routing. I would find an alternate route if needed. Good luck. Bruce |
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| torakki |
Aug 26 2025, 07:08 PM
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#12
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Member Group: Members Posts: 66 Joined: 5-October 18 From: Nor Cal Member No.: 22,545 Region Association: Northern California |
Yes Bruce, you were all over it. This morning, I ran new wires from the sender to the gauge and from the gauge straight to ground. I let the car idle for about 5 minutes and almost nothing. I started moving wire around on the back of the gauge and I noticed the temp went way up. That was with the ground disconnected. So, it appears I have a bad ground. Then I realized that my voltmeter wasn't working either. I hooked up the new good ground and now it works. Tomorrow, I'll redo the ground, and it "should" be fixed.
Thanks for all the responses and support. Photos are after idling for 10 minutes.   |
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