Where Is the Temperature Sending Unit on My 1988 Toyota 4Runner 3.0 V6?

The Toyota 4Runner first hit U.S. showrooms in the 1985 model year when the automaker decided to slap a cap on the rear of its pickup truck and give it a new name. The 4Runner followed the path the S-10 Blazer blazed two years earlier by focusing more on utility and comfort than rugged off-roading -- although the 4Runner could hold its own in the mud. The 1988 4Runner SR5 came fitted with a 3.0-liter V-6 engine and had a small thermo-resistor that read the temperature of the engine's coolant and adjusted its resistance to signal what the coolant temperature was.

Instructions

Locating the Temperature Sending Unit

1

Open the 4Runners hood.

2

Look on the rear of the intake manifold.

3

Find the two sensors screwed into the intake manifold. The sensor on the drivers side of the manifold is the 4Runners temperature sending unit.

Testing the Temperature Sending Unit

4

Allow the SUV to sit until its engine is completely cool; this typically takes two to three hours if you recently brought the engine to full operating temperature.

5

Pry upward and hold the locking tab on the temperature sending units wiring harness with a flat-head screwdriver, then unplug the wiring harness.

6

Set a multimeter to its ohm-testing feature and touch one of the multimeter probes to one pin inside the receptacle on the sending unit; touch the other multimeter probe to the other pin.

7

Read the ohms displayed on the multimeter screen. Compare the ohms on the display to the chart below, using the outside temperature since the coolant is roughly that temperature. If the ohms are not within this specification, replace the temperature sending unit. If the sensor tests within specification, proceed to the next step. Specifications are as follows: -4 degrees Fahrenheit should read 10,000 to 20,000 ohms; 32 degrees F should read 400 to 7000 ohms; 68 degrees F should read 2,000 to 3,000 ohms; 104 degrees F should read 900 to 1,300 ohms; 140 degrees F should read 400 to 700 ohms; and 176 degrees F should read 200 to 400 ohms.

8

Start the truck and allow it to idle until the upper radiator hose feels hot. Aim an infrared temperature reader at the upper radiator hose and pull the trigger on the reader to check the temperature of the hose. Add roughly 10 degrees F to that reading to compensate for the loss of heat from the hose. Compare that reading to the information in the prior step. If the sensor is not within specification, replace the sensor. If it is within specification, the sensor is functioning correctly.

Replacing the Temperature Sending Unit

9

Allow the vehicle to set until the engine is cool to the touch if the car recently has been driven. Partially open the radiator cap and listen for a hissing sound. If you hear a hissing sound, leave the radiator cap as is until the hissing stops. Remove the radiator cap. This relieves any residual pressure so the coolant level falls below the level of the temperature sending unit.

10

Pry upward and hold the locking tab on the temperature sending units wiring harness with a flat-head screwdriver, then unplug the wiring harness.

11

Remove the temperature sending unit with a ratchet and deep-well socket.

12

Check the threads on the new temperature sending unit for a coating of thread sealer. A red coating on the threads indicates thread sealer is present. If there is no red coating, apply a thin coat of thread sealer to the threads and allow it to cure for the time specified by the sealers instructions.

13

Hand-thread the temperature sending unit into the intake manifold and snug it with a ratchet and deep-well socket. You do not need to tighten the sensor much as the thread sealer is what prevents coolant from seeping through the threads.

14

Plug the wiring harness into the receptacle on top of the sending unit.