Yes it could be the sending unit. To check, you'll need a thermometer that reaches over 200 degrees.
With the engine cold, remove the rad cap and place the thermometer in the rad so you can see it. Start the car and allow it become hot. When the gauge starts going too far, check the thermometer. Normal operating temp is between 195 to 205 degrees. Compare the collant temp and the interior gauge to determine if the sending unit is the problem.
If it's working correctly, replace the cap and follow the same process with the cap on. Check the rad hoses. Specificly the lower one. Make sure it isn't collapsed restricting the coolant from circullating. If it or another one is, replace it.
If that isn't the problem, I would recommend that you remove the radiator and have it boiled out. Most likely it's plugged.
PS: I hope I helped you. If you have any other questions, don't be afraid to ask.
Thursday, October 16th, 2008 AT 9:53 AM