I have a 1988 Volvo 240DL and about 2 weeks ago, I started the car in the morning and in about 30 seconds, the temperature gauge rose to hot. I turned the motor off. A few days later, I tried it again and the same thing occurred. The next day, I just turned the ignition switch to on and the temperature gauge went to hot. My next step was to replace the temperature sending unit (2 wire) which feeds the computer. It was located under the 3rd cylinder and behind the air manifold. It took some time to conjure a method for removal and installation. Before installation, I checked the resistance of both old and new sensors with room temperature and hot water. The new sender seemed to respond a little better, ergo I installed the new one. With the ignition switch on, I checked the voltage at the 2 wire connector and is was about 5 volts. Now, I turned the ignition switch to on and the temperature gauge goes to hot again. Now, I replace the temperature switch unit (1 wire) which is under the 2nd cylinder and behind and under the air manifold. This temperature switch unit feeds the temperature gauge. This unit was easier to remove since I had not replaced the large vacuum hose yet. There were no tests or checks to perform. Again, I turn the ignition switch to on and the temperature gauge goes to hot. Now, I think that I have only to check the operation of the engine thermostat which I replaced about 3 years ago with a $21.00 failsafe thermostat. I drained the antifreeze, removed the thermostat and checked its operation. It opens at the stamped 180 degree F. Now, I have to reinstall the thermostat, refill the antifreeze and run the motor to remove any air pockets in the motor. And, of course, refill with more antifreeze as needed to maintain the correct level. Does anybody have any other suggestions?