Coolant Temperature Sensor/Connector (for EFI)

1990 XJ-S Coupe (US Spec, 5.3L V12)



¾” Deep socket/wrench

Coolant Temperature Sensor (Part Number DBC 3728 or DAC 4737)

Anti-seize compound

Connector (Calterm # 08653)

2” x ½” Heat Shrink Tubing

6” x ¼” Heat Shrink Tubing

Self-fusing Silicone Tape


The Coolant Temperature Sensor is used for EFI system.  It is located on the left-side coolant rail, near the front (by the thermostat housing), and the plastic part of the stock piece is black.  Don’t confuse this with the Coolant Temperature Sender (which is used for the dashboard gauge and is located on the right-side coolant rail), the Low Coolant Sensor (located on the Header Tank), or the Auxiliary Fan Thermal Switch (located on the Water Pump).  The word “Water” is sometimes used in place of the word “Coolant” for all these devices…


This device is a “Negative Temperature Coefficient Thermistor” - a resistor that changes it value as temperature changes.  It is easy to test as covered in “Experience in a Book” as well as at  When I unplugged this sensor (mimicking an open circuit in it) and tried to start the car, it started then stalled because the EFI system will not allow fuel to be injected.  Sean Straw has a web page that describes a switch you can make to carry in the car in the event of component failure on the road.


Although mine seemingly measured ok, I was doing so much other coolant system work this past winter that I thought I might as well replace it.


I got a sensor from (their part number IN105145) for $17.49 (they sent me a Lucas Sensor part number SNB802).  I changed this when I had the cooling system drained, so I didn’t have to worry about coolant spilling out.  Given its position behind the thermostat, I doubt much would come out anyway even if the system were full (as is the case when removing the Auxiliary Air Valve).  When replacing it, don’t forget some anti-seize compound on the threads.


Of course, the connector was old, brittle, and cracked – time for a new one.  It is the same connector used on the Fuel Injectors and elsewhere in the engine compartment.  My local parts shop had a couple of Calterm #08653 “GM Multi-Port Fuel Injection Sockets” in stock ($2.23 each) that is an exact fit.  Another parts store had an equivalent connector for $7.50 each – watch out.


The Calterm is black with two white wires about 6” long coming out – no “boot” supplied.  I used an X-acto knife to trim the top “barb” on the connector in order to fit the ½” heat shrink tubing over it to make a watertight boot (by heating the tubing with a lighter).  I then put ¼” heat shrink tubing over the “boot” for nearly the entire 6” length (leaving the bare ends of the wires exposed).  I cut off the old connector near where it splits out of the harness and took the small band labeled “Water” off, then sliding it on the new connector.  I stripped back the wires, and soldered on the connector (polarity does not matter).  I shrunk the ¼” tubing then used self-fusing silicone tape (from my local Sears Hardware store) to insulate and wrap the connection.  Plug it in.  Next project…













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