temperature sender on a 472 / 500ci V8

[L_Hammond]

Hi.  I have a 472ci V8 in a 1940's Caddie.  Not my decision.  The temperature sender unit in the engine appeared to be a switch type that got to a temperature, then operated a light on the dash.  I removed it to put in a temperature gauge under the dash (another spot was already taken with a temp sender for a thermo fan).  On removing the sender I was surprised to see it didn't go into coolant.  There was simply a recess/cup in place.  Is this normal?   I doubt a regular sensor could work in such a case.  Any ideas?

Cheers, Lloyd

[Phil Weber]

The water temp sensor sits behind the water pump just to the right of the thermostat housing in the block .
In the picture you can see the water temp sensor with the blue wire attached.

Phil

[L_Hammond]

Hi Phil.  Yes - that's where my sensor is.  Not sure if you've ever removed yours.  The issue I had was that it wasn't in contact with the coolant, which seems strange.  Maybe it's sufficient for this type of sensor to sit in a recess where the metallic shell/cup is a suitable thermal conductor.  Cheers, Lloyd

[hornetball]

That's a metal temperature sensor that is designed to actuate a last-ditch "STOP RIGHT NOW" light.  You should not use that for a water gauge.  You can wire it to your own "STOP RIGHT NOW" idiot light if you like.  It's a simple switch to ground and is supposed to ground at 260F according to the manual.

[Scot Minesinger]

The stop right now set at 260'F is measuring the temperature of the metal block, not the coolant.  You cannot put a temperature gauge sensor there and enjoy any meaningful information.  The 472/500 block provides two factory temperature indicators, one above water pump (below compressor clutch) that is where temperature gauge sensor should go that measures coolant temperature, and then the other which is discussed here, which just measures the temperature of the block.

[35-709]

The proper water temperature sending unit/location can just be seen in the far right of the picture above, below and to the right of the upper radiator hose connector and thermostat housing as you are looking at the picture.  The sensor to the left of center (with the wire connector unplugged) is the metal temperature sensor for the heater system which does not let the heater blower motor come on until approximately 120 degrees has been reached so one doesn't get cold air blowing on their legs and feet --- especially appreciated by the ladies.  That is NOT the "STOP RIGHT NOW" idiot light sensor.  The stop right now light (STOP ENGINE) sensor is located at the rear of the engine on the driver's side and that is the metal sensor that activates when the engine has overheated to the point that damage will occur if the engine is not shut down immediately.

Edit:  A shop manual is apparently called for here --- readily available on eBay.       

[TJ Hopland]

I'm repeating some of the above post but do have some new other details so I will just leave it.....

In the photo you can see a metal temp switch in the head with no wire connected to it but a possibly green wire near it.  This is a 'blind' hole that goes nowhere.  Its just sensing metal temp.   The alternator sits in front of it and that one trips at around 120*F.  Its part of the climate control system and allows the blower to run at higher speeds in some modes.  The idea is its not going to blow cold air on you, it waits till there is some heat in the engine.   

That sensor has a almost identical twin in the other head which would be back by the brake booster.  The one back there is the stop engine temp one that trips in the 260*F range. 

There are 2 coolant ports one of which you can partially see in the picture.  Its partially blocked by the timing cover and has the blue wire going to it.   Stock one for most cars was for a light and trips in the 230*F range.   The other coolant port a little to the right (if standing and looking at the front of the engine) below the distributor.  In most cars this was a thermal vacuum switch.   Both of these are in the same passage just a few inches apart so they both should be fully surmised in flowing coolant and give the same reading.   Some of the later possibly EFI motors had another coolant port sticking out the side kinda behind the water pump and above the oil filter.     

[DeVille68]

Interesting! On my 68 I have not found a wire that runs to the front of the passenger side for this special thermo switch. Nowhere in the shop manual is a switch / sensor for the activating the blower mentioned. There is only a vacuum delay on the firewall.
What year did have this feature?

Best regards,
Nicolas

["Cadillac Kid" Greg Surfas 15364]

Lloyd,
You have a lot of information above but I thought I might just add my 2 cents worth here. The "view from above" photo shows the relative positions of the two water jacket sensors.

The low water sensor is the one behind the water pump.  This location was chosen by the engineers since it is at a high point in the water jacket and a shortage of coolant would be evident there first.  This sensor is rated at 260 degrees F, and since at 16 or 16 pounds of pressure (the system cap) you cannot have liquid coolant, it must be super heated and thus the coolant level is low.

The "water temperature sensor is the location normally occupied buy the thermal vacuum switch and is probably the best place to install a temperature guage sensor.
Greg Surfas

[hornetball]

Interesting! On my 68 I have not found a wire that runs to the front of the passenger side for this special thermo switch. Nowhere in the shop manual is a switch / sensor for the activating the blower mentioned. There is only a vacuum delay on the firewall.
What year did have this feature?

1974 had it for certain.  Not sure about other years.

[TJ Hopland]

73 had both head sensors.   Wasn't there a temp gauge through 70?  Light came in 71?   

[DeVille68]

1974 had it for certain.  Not sure about other years.

I just remembered that the described feature is integrated into the heater water valve. There is a thermo / vacuum switch that only supplies vacuum to the master vacuum switch when the coolant is warm enough for the blower to come on.
So, some year later they must have switched this vacuum system over to an electric version with a corresponding sender on the front of the passenger side head.

To my knowledge the 68 has a temperature gauge. From the pictures above: the one to the right (passenger) is the temperature sensor and the one to left (driver) is the thermo vacuum switch for the distributor vacuum. The block heat sensor is on the driver side on the head towards the firewall.

Best regards,
Nicolas

[andrewjake3]

Fantastic guys...y'all have solved my problems. (1970 Cadillac Eldorado 8.2)
1. I have no 120 degree engine block sensor to turn on my heat.
2. I have no 260 degree engine block sensor to turn on my overheat light.
3. I need the front engine coolent sensor replaced because it slightly glows at normal temp.
4. I would also like to replace the coolant vacuum sensor just for measure.

Now where do I buy these sensors?

[andrewjake3]

I had to buy them used at the Cad Company....505-823-9340.  Albuquerque, NM.