1970s 1976 Eldorado metal temperature sensor

[shadetree39]

Among the spare parts I got with The '76 was a temp sensor. It is faintly stamped 44 and 7F
on opposite facets. The old sensor removed from the left rear cylinder head is stamped AO320M and 35 5 on an opposite facet. The caulking colors are the same.
The tang is broken off and judging by the connector its been a long time. It will buzz an alarm when grounded.
So, what do I have ? Is this the correct replacement or is it for the one in the r/h
head?

["Cadillac Kid" Greg Surfas 15364]

If the grounded wire buzzes (activates the buzzer in the car) it s the "Stop engine" sensor for the driver's side head. Grounding the wire to the sensor in the right side haed will allow the AC/heater fan to run.
Greg Surfas

[TJ Hopland]

The one in the right head always tripped at 120*f and was used over many years.  The right head one trip temp varied over the years and models but I think the trip temp was always at least 270*F.  I don't ever recall any sure way to identify them other than to slowly heat them up with a meter connected to them. 

[shadetree39]

I was hoping for an easy ID of the sensor, oh well. Ill sneak out the candy thermometer and boil some water. If it doesn't fire once above 150 deg. or so I'll go with it.

[SaltLife97]

I have found all three sensors as New Old Stock items off of eBay once. There is the Climate Control thermo-delay switch, the Engine Metal Temp switch, and the coolant temp switch. The one in the passenger side head is your climate control delay switch. That is for the cold seasons. Let's say you left the climate control switch on "Auto" or "High" from the last heater session, you wouldn't want the climate control blasting you with frosty winter air while the car heats up. So once the wax bulb inside that switch expands from the 120 degree minimum heat, it'll complete that ground like mentioned above and allow the climate control blower to kick on with lukewarm air. The coolant temp switch completes the ground at 320 degrees (yes you read that right).Finally, the back up to the coolant overheat is the engine metal temperature switch which the book doesn't mention an actual number but instead says it turns on when the block is excessively hot. You can imagine if THAT light turns on, you're about to melt the block.

[shadetree39]

Thanks for the explanations. As stated the one I removed from the driver side head was stamped 320 to agree with your description. the nos one one I have is still a mystery. Ive yet to test the one I have.

[shadetree39]

I posted earlier regarding a temp sensor I got with the car trying to determine if its usage. the sensor on the left rear head had its tang broken off and still in the green wire connector. I couldn't successfully test it so i installed it a started the engine it didn't take but a few minutes to set off the stop engine light. Its no doubt the 120 degree item. No success yet finding a 320 degree item but its of a low priority.

[bcroe]

If I find mine you can have it.  It was in my
5.7L, but I sold that low mileage engine 20
years ago, when I put in a 6.6L.  Bruce Roe

[shadetree39]

Hi Bruce. Sorry so late with reply. I'll be sending you an ECU to check when I get back home from a road trip. I have (2) as you may recall but it couldn't complete the fuel pump circuit with the one original to the car. The backup unit worked fine and it fired right up. I've yet to install to the relay per instructions. 

[SaltLife97]

Not for nothing but these sensors and the wax they used inside them for thermal expansion require more of a small butane torch on the sensor end. Boiling water simply isn't enough for a quick read since the heat transfer from the water, to the metal sensor casing, to the wax inside it takes a LOT of heat before you get any confirmation of it working. Engine metal to metal sensor casing allows for much quicker heat transfer thus allowing either: the AC Blower to actuate above 120 degrees engine heat ( keeps the auto climate from blasting you with cold air during the winter season) OR the engine metal overheat to illuminate on the dash. So try a small butane torch for a cigar or something before your AC blower kicks on above 240 degrees and the engine "overheats" at 120

[bcroe]

the Engine Metal Temp switch

Finally, the back up to the coolant overheat is the engine metal temperature switch which the book doesn't mention an actual number but instead says it turns on when the block is excessively hot. You can imagine if THAT light turns on, you're about to melt the block.

Do you know the part number for that sensor, or
how to identify it?  Bruce Roe

["Cadillac Kid" Greg Surfas 15364]

Heater turn on is AC Delco D-1870. The high temperature alarm sensor is AC Delco D-1872 or GM # 25036581.
Greg Surfas

[Phil Weber]

These are pictures I have of two NOS sensors from my spares box. They have the temps etched on them otherwise ( appearance wise ) they are the same.

Phil

[bcroe]

Thanks for the info.  I found a couple which
looked exactly like the picture, but found
no numbers like the above.  I cannnot imagine
where they came from, except out of some Cad
motors here.  Bruce Roe

[Terry Griffin - CLC#20149]

Had a nasty experience with a lower radiator hose leaking and dropping all the water on my '75 Eldorado.  The coolant temp switch didn't activate as it was sitting in hot air, not boiling water, but the engine metal temp did.  By which time the motor was making that horrible tinkling sound and was toast.  The replacement motor is monitored by both water and oil pressure gauges installed below the dash.

["Cadillac Kid" Greg Surfas 15364]

The sensor in the front center of the block, under the compressor is the low water sensor. It is designed to activate when due to low water in the block the temperature of the sensor is that of the "superheated steam" in the void (no coolant).
I don't know the exact temperature but it is probably something like 260 degrees F. This is just the localized temp because at first alarm there is still coolant in the critical places. This sensor often becomes disconnected when changing the AC compressor.
Greg Surfas

[79 Eldorado]

If the 44 7F does not refer to the PN or temp setting it might be a date code.

Also be aware that there are at least 2 near identical sensors which have different threads. If you see them side-by-side it's pretty obvious but if you are hunting images on eBay look carefully at the threads. I initially thought the coarse thread was for aluminum intakes. My 1979 Eldo did have coarse threads, with aluminum intake, but the older cast iron 76-77 Seville intake I bought from Bruce also used the coarse thread version. I identified the coarse thread version as PN 6490043. The fine thread version I found was 6489307 and also known as TS60. The 6490043 controls the blower delay.

My original was marked AC95M on one side and what looks like one of the following on another side:
2908
29C8
29C3
2903

Scott

[TJ Hopland]

I think the different thread version was metric for engines like the 4100 perhaps?   It was years ago when I was looking for one version of the sensor(s) and they were NLA but I found the other version and was able to make them work.  They are blind holes so you are not really trying to seal or hold anything other than the sensor in contact with the metal.   

My guess is I was able to find the later metric sensors and I used them on an older engine, possibly a diesel.  On the diesels the metal temp switch threaded into a special head bolt.  It was long enough ago maybe it wasn't metric and just a different thread pitch.  I don't even remember but was the 4100 all or mostly metric?  I think the diesels were the annoying mix where they were mostly SAE but just to mess with you threw in some metric stuff.