1972 Temp Warning Light

[Cadillac Nut]

I had my '72 Fleetwood running the other day (just idling for about 10 minutes) and out of the blue the temp warning light and buzzer came on.  The engine showed no signs of overheating and there is plenty of coolant.  Any ideas?   This is the only Cadillac I've ever had with the "idiot" warning lights.   (all my others are earlier)

[Mike Josephic CLC #3877]

Could be just a bad coolant temperature sensor.  Check
your shop manual. it's located on the block.

https://shop.advanceautoparts.com/web/SearchResults?storeId=10151&catalogId=10051&langId=-1&searchTerm=coolant%20temperature%20sensor

Mike

[chrisntam]

Get one of those IR temp guns, cost is $15 to $20, it will tell you how hot the engine is.  Point it at the sensor area, the upper and lower hose to see what it says.  Up to 500 degrees is fine for engines, if you want the get the temp of the exhaust manifold, get one that goes to 1000.  Handy little tool to have.

Service manual also tells how to troubleshoot the indicator lights.

If both the coolant light and the block warning light came on, I'd be checking as to why.  They are separate sensors.  If it did get that hot, wouldn't the coolant be burping into the overflow bottle?

[The Tassie Devil(le)]

Was the "Engine Stop" light illuminated?

Bruce.

[TJ Hopland]

Good advice on getting one of those IR guns and seeing if there is anything unusual going on under the hood.

I too was going to ask which light?    72 has 'engine temp'?  and 'water'?  I think adding stop to one of the lights came in the later 70's.   I don't think the water one operates the buzzer?

That whole circuit with the buzzer is a mess that changed slightly year to year.   Basically several systems share one buzzer.   That's easy with an electronic control module and some software but not so easy with just wires and switches.  You can easily get a lot of unintended interaction between the systems from just one loose connection somewhere.  Does anyone know if the 72 had that system tied to the seat belts?   73 and up did and that was usually where I found the issues related to someone in the past trying to bypass the seat belt part because they didn't want to use the belts. 

[Big Fins]

It was also tied to the key being in the ignition.

[The Tassie Devil(le)]

Actually, the Stop Engine light is related to engine overall temperature, and that temperature is getting to the engine seizing point, and way above the water boiling point.

I know because I have experienced the Stop Engine light come on, and it wouldn't allow me to restart the engine until it had cooled down after about a half an hour.   The engine would crank on the Starter Motor, but no ignition to fire the plugs.   I was trying to start it so I could start adding water to replace the water that had escaped due to me forgetting to reinstall the radiator cap before heading off on a trip.

The engine got so hot that wiring in the engine bay started to melt, including the Plug Wires.

Bruce.

[dplotkin]

(just idling for about 10 minutes) and out of the blue the temp warning light and buzzer came on.... 

I smell a failed fan clutch.

Dan

[Cadillac Nut]

It's what TJ Hopland said-- basically, an electrical gremlin.   It would start coming on when I opened the door, when the engine wasn't even running    It randomly (occasionally) happens and goes away now so obviously I have a loose connection somewhere or need to clean a ground.  But where......  The seat belt warning light also comes on only when you are in certain gears and only when it feels like it....

[TJ Hopland]

You should check and play with the park neutral switch.   Get an assistant or back up to something and see if the reverse lights are coming on when they should.   Also carefully (foot firmly on the brake) try starting it in gears other than P or N.   If that isn't aligned or working properly that could be throwing off some of the other functions that are tangled up with it and just making things more confusing to trace.