This is my first post here so it might be a little lenghty.
I have a 1968 SDV with a 472cc engine. The temperature gauge is acting up. If the car had been sitting in the garage for a while and I start it, let it run on idle, it takes about 3-4 minutes to gauge the coolant temperature as 'hot' and trip the dash alarm. I decided to take the termostat out and start it back up. It took me almost and hour to get the damn thing out and when I restarted the engine, it took less than 10 seconds to gauge the temp as 'hot' and trip the alarm.
I currently have the factory shop manual on order but I was informed that it may be the coolant temperature sender. Since I do not have any of the system schematics, would there be another possiblity which causes the alarm to trip? (mechanical parts, electrical components, etc.) The hoses are all fine, the rad is full of coolant but I am unsure of its concentration , altough, I believe it should be ok.
I noticed on my 472 that the front coolant temp sensor that is right below the A/C compressor in the block that the wire was corroded and would make my temp gauge off. once the wire was repaired/replaced it worked fine.
I would get a new thermostat , 180 degree, and make sure it is a cadillac thermostat... they have a piece on the bottom that goes in a port hole in the block... but I don't think that is your problem... but you have to put the thermostat back in , so best to put in a new one...the sensor that has gone bad should just be disconnected...look at the cylinder head on the drivers side.. at the end next to the firewall... if you look at the rocker arm cover to the end of the head , in that few inches you will see the sensor with one wire going to it...unplug that wire and your alarm will not go off...