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74 Eldorado Temp Sensor quandary

Started by danjarrett1, January 06, 2018, 06:59:26 PM

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danjarrett1

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”
1985 Cadillac Eldorado

35-709

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 - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

"Cadillac Kid" Greg Surfas 15364

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
Director Modified Chapter CLC
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-

danjarrett1

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”
1985 Cadillac Eldorado

danjarrett1

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”
1985 Cadillac Eldorado

danjarrett1

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”
1985 Cadillac Eldorado

danjarrett1

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”
1985 Cadillac Eldorado

35-709

#7
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.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

danjarrett1

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”
1985 Cadillac Eldorado

35-709

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 - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

danjarrett1

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”
1985 Cadillac Eldorado

35-709

Speaking of the others here, I respond, "INDEED"!   ;D
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

"Cadillac Kid" Greg Surfas 15364

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
Director Modified Chapter CLC
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-

danjarrett1

Sounds good, how do I go about purchasing them from you? 
1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

"Cadillac Kid" Greg Surfas 15364

Dan,
I will PM you. If you don't get the PM let me know on this forum.,
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
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-

danjarrett1

1974 Cadillac Eldorado convertible
2007 Cadillac Escalade
1980 Cadillac Seville “Bustleback”
1985 Cadillac Eldorado

Cabinlake26

Hey all - I'm new to this group. I have a '74 Eldorado Convertible.

I ran across this thread when trying to figure out why my temperature warning relay buzzer and dash light keep coming on intermittently.

The buzzer will start and stop while driving (usually when going over bumps) and even when the vehicle is off and the keys are out of the ignition -- in some cases I'll walk in the garage in the morning and the buzzer is sounding.

I was planning on ordering a new sensor and warning buzzer relay. In reading the forum posts it sounds like GM #6490394 (located on the left rear cylinder head) is the sensor linked to the warning relay buzzer.

Am I accurate in the assumption that is the proper sensor (linked to the warning relay)?

Any guidance is appreciated.

Thank you!

Rick

TJ Hopland

I don't have a diagram handy but I don't think the metal temp sensor in the head would activate the buzzer with the key off so I would not be starting there or with the buzzer itself.  I would just make sure the wire is connected to the sensor and not obviously damaged anywhere you can easily inspect it.

I think we have at least one more thread possibly also on a 74 on this subject going right now.   That buzzer is tied to multiple systems and unlike a more modern car with a body control module this is all being done old school.  Some work off ground and others work off positive so a possibly minor fault in one of those sub systems can cause odd interactions.   

Because the seat belts were involved in the system that is where I usually find the issue.  Sometime in the past someone tried to bypass the seat belt alarm function.   It may or may have worked at the time and it may or may not have survived well over the years.  I have found things like masking tape holding wires together under the seat.   I have also found where some object under the seat damaged or disconnected wiring under the seat when the seat was moved. 
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

DeVille68

The engine gauges should only receive power then the key is in ignition or start position. I guess you have some wiring issues. Check the wiring to the engine temp sensor (usually gets hard and brittle due to temp and age) and the bulk head connector on the firewall.

Best regards,
Nicolas
1968 Cadillac DeVille Convertible (silver pine green)

O. Ramirez

Hi I’m new to this forum, sorry I don’t know how to make my own post lol but my 73 coupe Deville is missing the engine temp sensor behind the alternator might that be the problem my ac or heater doesn’t work or what’s the purpose of that sensor?