Engine metal temperature sensor

[brianl703]

I was looking at the wiring diagram for the 1984 Cavalier to see if I could upgrade to a cluster with a tach. The answer is yes, but I'd have to re-pin the cluster connector and add a tach wire.

I noticed that there are actually TWO temperature sensors on the engine. One is a regular temperature sender (either a switch if it only has warning lights, and a thermistor if it has gauges--this car only has warning lights, which is why it has no tach), and one is an "engine metal temperature sensor" which is a switch that will make the gauge peg out (or turn on the warning light).

I suppose the engine metal temperature sensor is there to make sure that an overheat condition is indicated even if all the coolant is gone from the engine, since my understanding is that a regular temp sensor could read normal or even cold if all the coolant is gone.

The only other vehicle I know of that has something like this is the Crown Victoria, where it's used by the PCM to put the engine into overheat mode where it runs on alternate cylinders.

Doesn't seem like most engines have a sensor like this, so if all the coolant has left the engine, a driver wouldn't know the engine is overheating.

 

[Jetronic]

it depends on the design, some sensors do get heat from the head they're screwed through. But the takeaway is, investigate if the temperature gauge doesn't rise.

 

[JohnnyG]

The Northstar had to have something like that as well. (Not seen it personally) Something would have had to activate the "Limp home mode" which, as you say would cause the engine to run on alternate cylinders if an overheat condition was detected.
It would also limit the top speed to 50 mph.
The idea was to prevent further engine damage. Most reports from back then said it didn't prevent anything.

 

[CorvairGeek]

GM used these on at least some of the Chevy 6s (194/230/250/292) too. My 292 has a very large diameter one, unlike the small diameter one used on the Cavalier (2.0L) engine. I assumed it was an 70s-80s GM inline engine thing.

 

[Timmastertech]

Ford has been using cylinder head temperature almost exclusively for years vs a traditional coolant temp sensor. Your thought is correct, a coolant temp sensor has to be in coolant to sense temperature accurately, if coolant level is low and the sensor has air around it it will not accurately report temp. The temp of the actual metal is far more accurate