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Randall C
Randall C, ASE Master Tech
Category: Chevy
Satisfied Customers: 12803
Experience:  ASE Master, L1, 32 years, Diagnostic / Electrical Specialist
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91 Lumina: quit working..litre..I installed new sending unit

Resolved Question:

My temperature guage in my 91 Lumina quit working. 3.1 litre Euro model. I installed new sending unit and the ohms resistance goes down when you warm up the sender, so it appears to be working. I have 5 volts going to the sender (between the yellow and black wires). the guage will not come up at all as the engine warms up. I does go all the way hot and the overheat lite comes on if you turn the key to just before it cranks the starter. As soon as you release the ignition key or just put it in the on position, the guage goes to all the way cold. I just put in a replacement (used) engine. Is the problem with the ECU ? where is the problem? I dont want to run this engine without a temp guage working.
Submitted: 6 years ago.
Category: Chevy
Expert:  Randall C replied 6 years ago.
Hello, I think you changed the coolant sensor. The guage is controlled by a smaller one wire sendr located in the cylinder head. Unortunatley, i can not remember which head nor exact location but will be a small brass sender and should have one DARK GREEN wire going to it.

his temperature indicating system consists of a sending unit, located on the cylinder head, electrical temperature gauge and an instrument voltage regulator. As engine temperature increases or decreases, the resistance of the sending unit changes, in turn controlling current flow through the gauge. When engine temperature is low sending unit resistance is high, current flow through the gauge is restricted, and the gauge pointer remains against the stop or moves very little. As engine temperature increases sending unit resistance decreases and current flow through the gauge increases, resulting in increased pointer movement.

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