Ok I have a 1970 DeVille and for as long as I have owned the car when I pull the key out of the ignition the "Engine Temp" light comes on until I get out and close the door. Well recently, on the hottest day of the year mind you, the "Water Temp" light came on. Now this was a new light for me so I pulled over and took a look, no steam, no leaking, no nothing. I waited a while and let the car cool down and drove her home. A week later I dropped her off at my mechanic and he ran some tests. He gave me a call later that day thinking that it is electrical. He ran it on an infared scope of some sort and said he could not get the thing to go over 193 in temp and the radiator was full and showing no signs of leaking. Ok cool I thought, I can deal with that.

Well the problem is that the light never comes on when it is 85 or cooler and on drives less than 20 minutes or so. It only comes on when the day is over 90 and I start pulling some distance on the car. Just the other day it was 93 and the light came on. I was going to ignore the light, but when it was that hot out and im not use to seeing this light I had to pull over, I just couldnt risk it. Again, no leaking or steam or anything, but I pushed my ear close to the radiator and that thing was boiling like crazy. I had never heard it boil so loud.

What do you think? Should I get a second opinion? Just replace the thermostat? Or should I get myself a gauge and see what happens with the temp when I can actually get a reading instead of a light that goes on or off?

Couldn't hurt get a gauge...

The sensors can become inaccurate with age so you might try replacing the water temp sensor to see what happens. The gauge is really the best idea so that you will know exactly what is happening.

Steve B.

Spoke with the mechanic today and he thinks it is the temp sensors too. Where is the best place to get new ones?

You might be able to get a stock sensor from Autozone/Advance/pick your chain store.
If not a Caddy dealership parts dept. should be able to hook you up.

An Autometer gage comes with new sender and will screw in place of your sensor at the front of the block. You can even use the stock wire if you want, just pull the dash pad up and unhook the wire that goes to the temp gage on your dash bezel, and connect it to the gage. No messy wiring that way. About $45-50 for a decent gage.

The Engine Temp idiot light is connected to the back of the pass. side head. It is also connected in line with a bunch of other stuff, including the door "open" switches and courtesy lights. Mine also lights this light when the passenger side door is open, I just leave it alone.

Cool. Thanks again for all the help.

Replaced the sensor, replaced the thermostat, and just for kicks flushed the system. I have owned her for 5 years now, so it seemed about time. Weather has been in the 90's and I have been logging miles, I havent seen that light again. Thanks again everyone for the suggestions.