Author Topic: 74 Eldorado Temp Sensor quandary  (Read 145 times)

Offline danjarrett1

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74 Eldorado Temp Sensor quandary
« on: January 06, 2018, 05:59:26 PM »
gentlemen:In my attempt to establish a baseline on my 74 Eldorado, I considered installing engine gauges so I might get an accurate representation of what the engine is doing. I really didn't want to screw up the lol of the dash and after reading several forum replies, I’ve convinced myself to leave factory well enough alone. I did however, order and “engine temp”sensor to install after discovering a dangling wire with a plug on it, near ther rear of the alternator, I also discovered what looked like the remains of a previous temp sensor that was over torqued and broke off in the cylinder head. I thought that this was the coolant temp sensor, I have learned however, for the CLC forum replies  that it is a dry hole. So. I have a brand new sensor that I ordered, I requested and engine coolant temp sensor...and now,  I know the  coolant temp sensor is under the AC compressor and appears to be working.  Question: if I do, in fact, have a coolant temp sensor, it is interchangeable with the sensor behind the alternator that drives environmental in the cabin? Are all three temp sensors triggered at the same temp?....if not and I need a sensor for the automatic heating/cooling system, what is it called and where can I get one??
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Online 35-709

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Re: 74 Eldorado Temp Sensor quandary
« Reply #1 on: January 06, 2018, 07:57:35 PM »
Only the coolant temp sensor under the AC compressor is "wet".  The sensor under the alternator is an engine  temp sensor (not coolant) and kicks in at about 120 for the heater fan.  The temp sensor at the back of the engine by the left cylinder head is a metal temp sensor and that kicks in at about 350 (or maybe 375 it is in your shop manual) and if it does activate and the light and buzzer come on you shut the engine down NOW because serious and expensive damage is about to be done.  The two engine metal sensors, the one for the heater blower and the high temp one at the rear look the same and you don't want to mix them up!  They are not good for any other purpose I can think of.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold
1950 Jaguar Mark V Saloon resto-mod

Offline "Cadillac Kid" Greg Surfas 15364

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Re: 74 Eldorado Temp Sensor quandary
« Reply #2 on: January 06, 2018, 08:29:24 PM »
Dan,
You say you have ordered the sensor, but for your reference I have "bumped" my adv. for these sensor with pictures in the "for Sale" section of the forum so you can see the sensor you describe. By the way, the old, broken off sensor can be removed by just driving a screw driver or small chisel into the old "stub" enough to turn it out.  These are dry holes and the metal temperature is what is being "read".
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #3 on: January 06, 2018, 10:48:13 PM »
So, the two engine temperature sensors that measure engine temperature do have different trigger limits! I will try to find the pics and correlate them to the one sensor I have. Does anyone have a source for the two engine temp sensors, I believe what I have received is a coolant temp sensor.
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #4 on: January 06, 2018, 10:52:09 PM »
Greg:are those sensors pictured for sale or just examples of what I should try to find?
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #5 on: January 06, 2018, 11:08:40 PM »
Here are a few pics of the sensor I received. There was no documentation for the sensor (I know, my bad) I bought in on eBay as it was advertised and a engine temp sensor. I ordered it some time ago before I was awake there were three sensors related to temp. Can anyone of you guys tell me if this sensor is the coolant, heat-fan sensor (on the cylinder head, below alternator)  or the engine metal sensor ( on the back of the head)
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #6 on: January 06, 2018, 11:24:28 PM »
Found my order data from eBay...see attached photo! I guess this is in fact a engine temp and not a coolant temp, but is it the one for the front right cylinder head location or the left rear location?
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Online 35-709

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Re: 74 Eldorado Temp Sensor quandary
« Reply #7 on: January 07, 2018, 09:54:47 AM »
The one you have, GM #6490394, is for the left rear cylinder head.  I know of no way to tell the difference, visually, between the left rear sensor and the right front (heater blower motor temp) sensor except by the part number on the box.  There may be markings on the body of the sensors themselves that indicate what they are but I am not familiar with what they might be.  FYI, the GM part number (aftermarket sender numbers will be different) for the right front heater blower temp sensor is 6489307. 

Pics of the engine coolant temperature sender (GM #6490715) are below.
« Last Edit: January 07, 2018, 09:59:10 AM by 35-709 »
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold
1950 Jaguar Mark V Saloon resto-mod

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #8 on: January 07, 2018, 09:58:43 AM »
Thank you for clearing that up! The one that is broke off in the cylinder head is the heater fan engine temp sensor under the alternator, actually...I want to replace all of them to get a good baseline on temp data moving forward. Do you have to have a resource or part number for the sensor under the alternator? Are these sensors still available from GM? I’ve looked on caddy daddy and OPGI wil no luck.
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Online 35-709

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Re: 74 Eldorado Temp Sensor quandary
« Reply #9 on: January 07, 2018, 10:03:55 AM »
I edited my post above to include the part number for the sender under the alternator --- 6489307.  Only the coolant sensor will provide any sort of "temp data".  The sensors Greg Surfas has are for sale, since you have the rear one just get the one from him for "under the alternator", the heater blower motor sensor.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold
1950 Jaguar Mark V Saloon resto-mod

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #10 on: January 07, 2018, 10:06:32 AM »
Sounds good! Thanks so much....I am new to this forum but I cannot believe the wealth of knowledge and detail out there! You guys all rock!!!
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Online 35-709

  • Posts: 2890
  • The most valuable antique is an old friend.
    • CLC Member
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  • Name: G. Newcombe
Re: 74 Eldorado Temp Sensor quandary
« Reply #11 on: January 07, 2018, 10:10:50 AM »
Speaking of the others here, I respond, "INDEED"!   ;D
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold
1950 Jaguar Mark V Saloon resto-mod

Offline "Cadillac Kid" Greg Surfas 15364

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Re: 74 Eldorado Temp Sensor quandary
« Reply #12 on: January 07, 2018, 10:15:13 AM »
Dan,
They are for sale hey are NOS OEM sensors and have been factory certified to
"close" at the correct temperature.
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline danjarrett1

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Re: 74 Eldorado Temp Sensor quandary
« Reply #13 on: January 07, 2018, 10:17:58 AM »
Sounds good, how do I go about purchasing them from you? 
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

Offline "Cadillac Kid" Greg Surfas 15364

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Re: 74 Eldorado Temp Sensor quandary
« Reply #14 on: January 07, 2018, 10:38:59 AM »
Dan,
I will PM you. If you don't get the PM let me know on this forum.,
Greg Surfas
Cadillac Kid-Greg Surfas
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline danjarrett1

  • CADZILLA
  • Posts: 61
  • CLC Member #31119
  • Name: D Jarrett
Re: 74 Eldorado Temp Sensor quandary
« Reply #15 on: January 07, 2018, 11:16:57 AM »
Greg:sent you a PM
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”

 

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