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 tempâ€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??
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.
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
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.
Greg:are those sensors pictured for sale or just examples of what I should try to find?
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)
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?
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.
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.
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.
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!!!
Speaking of the others here, I respond, "INDEED"! ;D
Dan,
They are for sale hey are NOS OEM sensors and have been factory certified to
"close" at the correct temperature.
Greg Surfas
Sounds good, how do I go about purchasing them from you?
Dan,
I will PM you. If you don't get the PM let me know on this forum.,
Greg Surfas
Greg:sent you a PM
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
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.
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
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?
That sensor will not allow current to the blower
motor until the coolant reaches the proper
temperature. It was a small part of the effort to
reduce emissions on those cars -- to provide a
faster warm up. See earlier entries in this post
for pics and more info.
Mike
Welcome Oscar,
The sensor behind the Alternator is there to monitor the engine temperature as it warms up, so that when the heater is operated, the occupants aren't blasted by cold air.
As soon as the coolant temperature is sufficiently warm enough, the sensor will then allow the warm air to flow.
For information, the one that looks the same, which is on the rear left cylinder head only senses when the engine block is getting too hot, and about to seize, and the alarm goes off, telling the driver to STOP ASAP. This usually happens when the engine looses all the coolant.
Bruce. >:D
To test if that sensor (or lack of) is the problem just ground it. With it grounded the system thinks the engine is warm and will let the blower run in all modes.
Sweet will try that tomorrow. Thank y’all! Y’all guys are awesome