For Z32 owners who are having overheating problems, this item is onlyone of the many to be considered in seeking a solution. However, if allthe common causes have been checked and vehicle overheating primarilyoccurs during periods when the fan should be running, certainly the fanand its control system becomes a prime suspect. 

Operating principles:

In the Z32, the electric fan located in front of the radiator (a pusher)is an auxiliary unit designed to come on under very specific conditions,providing extra cooling capacity when needed.  In many situationsthese operating conditions may never be met and the fan may never comeon. 

This auxiliary fan serves to assist both the cooling system and theA/C system. In addition to adding radiator cooling capacity related tooverheating, it also improves A/C condenser heat exchange, therefore A/Coperation. 

The NA Z32 has a single speed auxiliary fan. The following specs arefor the NA fan, and come from the Nissan service manual. Temps are in Fahrenheit:

A/C off, coolant temp below 219 = fan off
A/C off, coolant temp above 221 = fan on
A/C on, vehicle speed < 24mph, coolant below 201 = fan off
A/C on, vehicle speed < 24mph, coolant above 203 = fan on
A/C on, vehicle speed > 25mph, coolant below 219 = fan off
A/C on, vehicle speed > 25mph, coolant above 221 = fan on 

The TT Z32 has a two speed fan. The following specs are for the TT fan,and also come from the Nissan service manual with temps in Fahrenheit:

A/C off, coolant temp below 219 = fan off
A/C off, coolant temp above 221 = fan on
A/C on, vehicle speed < 24 mph, coolant between 194-210 fan = lowspeed 
A/C on, vehicle speed < 24 mph, coolant above 212, fan = high speed 
A/C on, vehicle speed > 25mph, coolant below 219 = fan off
A/C on, vehicle speed > 25mph, coolant above 221 = fan on 

As you can see, the fan is ECU controlled (A/C, temp & speed sensorinput feeds to ECU, output from ECU for fan operation).  It is alsoobvious the fan should not run very often if the cooling system is operatingefficiently.

Diagnostics:

1. Observations: Make sure the fan blades are clear of all obstaclesand can turn freely. Their position on the lower part of the Z tends tomake them subject to debris collection. I have found plastic bags wrappedaround mine and a hunk of styrofoam wedged such that the fan could notturn.  Also check 10 amp fuse marked air cond on relay box cover(front of the driver's fender hump under the hood) (1.) and checkthe fusible link marked rad fan in the box directly in front of the battery(2.). 

2. System check (read the notes at the end before starting this step):To force the system to behave under the non-speed sensitive conditions,slide a thin piece of cardboard (like an unfolded cereal box) (3.)down between the radiator and A/C condenser (just in front of the radiatorcap) to obstruct airflow from the engine fan (which is a puller). Ona hot day, just partially restricting airflow may work. On a cool day orwith a very efficient system, it may be necessary to remove the two topradiator brackets to completely block the airflow across the entire radiator. 

On a real cool day the coolant temperature may not rise enough to successfullyperform this test. Start the engine, turn the A/C on and monitor the tempgauge and fan operation. When the gauge gets somewhat (1/8th to 3/16s ofan inch) above its normal position, the fan should come on. If it does,OR if the temp gauge begins to approaches the H mark and the fan has NOTcome on, remove the cardboard, turn the A/C off and turn the heater onfull hot. Let engine continue to run until engine temp returns to normal.

If fan does not operate then troubleshoot starting with step 3, Circuittest. 

If the fan does operate, it is unlikely the fan operation is the causeof the overheating problem.

Note 1: This trick will not hurt the car as long as it's not allowedto get too hot or be too prolonged a period of time. The heater assistsin the cool down by exiting heat into the cab, and is a good trick to rememberif it overheats on the road to control the temp until it can be serviced.

Note 2: Making a hole about an inch from the edge of the cardboard andtying a string to it will allow for easy retrieval if it slips too fardown.

Note 3: The system check is good operational check of the system butnot entirely necessary for troubleshooting the system.  If desired,simply proceed to step 3, Circuit test. 

3. Circuit test: Test the circuitry without the temp sensor in the circuit.Remove the connector for the temp sensor. The open circuit will cause theECU to detect a problem. A short circuit can be created by placing a jumperwire into the connector. This signals an overheat condition to the ECU. Start the engine and a visual check will confirm if the fan comes on. Thetemp sensor is the yellow connector to the right of the gauge sender (4.).

If fan doesn't come on, go to step 4, Fan relay test. 

If fan does come on, go to step 6, Temp sensor test.

4. Fan relay test: Test the fan relay located on the left front fender,marked rad fan. Do this by turning the headlights on, then off, to provethe headlight relay is good. Then swap the fan relay with a headlight relaymarked headlight lh (or rh).  Check headlights again.  If theywork normally, the fan relay is good. The fan relay is in the front fuseblock, shown relay out (5.).

If the fan relay proves bad, repeat step 3, Circuit test, with the goodheadlight relay in the fan relay position. 

If the fan still does not run, go to step 5, Power supply test

If the fan now runs, its time for a new relay. Install the relay andyou can repeat step 2, System check, or step 3, Circuit test, to provethe cure. 

5. Power supply test: Test power supply to relay box with a voltmeter.Remove rad fan relay. With ignition on, check for battery voltage atthe 2 terminals which face the headlight on the driver's side by placingthe black probe on any ground, then checking each terminal with the redprobe (6.). 

Note: A test light can be substituted for the voltmeter by clippingthe lead to ground and then touching each terminal with the probe. Thetest light brightness level should be similar what you see with a batterytest. Use of a high impedance digital volt-ohmeter provides safety factorsnot present in a test light.  It is possible that a test light probein the wrong place could cause damage where the ohmeter would not. Usecaution.

If the terminals both test good, go to step 5.a, Fan/Harness test

If the either or both terminals test bad, check 10 amp fuse marked aircond on relay box cover and check fusible link marked rad fan in thebox directly in front of the battery. (see pics in step 1, Observations)

5a. Fan/Harness test: Check fan operation by placing a jumper acrossthe two relay terminals closest together.  Expect light sparks atthe jumper when contact is first made; this should be providing directbattery power to the fan.

If the fan runs then reinstall the relay and repeat step 3, Circuittest. If there is voltage at both relay terminals, a good relay, and agood fan /harness, then the fan should have worked under step 3, Circuittest.

If fan does not come on, check harness connector at fan (remove, clean,reinstall) and re-test. If the fan still does not come on, test the motordirectly. This will require a pair of jumpers directly from the fan connector(fan side) to the battery. Make the connections to the fan first, thenthe battery. Expect light sparks at the moment of connection. 

If the fan still does not run, fan replacement is required. Replaceand repeat step 3, Circuit test.

If the fan does run there is a wiring harness issue between the relayand the fan connector that may require a shop manual, special tools orprofessional assistance to find and repair. This is not covered on thispage because of its rarity.

Note: Monitor the condition of the fuse and/or the fusible link thatwas replaced for a period of days after getting the system restored. Ifthey fail again, there is a problem in the wiring or components that mayrequire a shop manual, special tools or professional assistance to findand repair. This is not covered on this page because of it's potentialcomplexity. Never use a larger rated fuse or link to solve the problem;to do so is a fire hazard. 

6. Temp sensor test: If step 3, Circuit test, causes the fan to run,the only circuit item not checked is the temp sensor (4.). Testthe sensor by measuring its resistance with an Ohm meter when the engineis cold and then again hot.  Readings should be between 2 to 3 K-ohmscold (68 degrees F ) and .30 to .33  K-ohms at 176 degrees F (~ normaltemp). 

If the sensor tests bad, replace and repeat step 2, System check, toprove the cure.

If the sensor tests good, make sure the terminal connections are cleanand make good contact, then repeat step 2, System check, to prove the cure.

Conclusion:

At first reading, these procedures may seem overly involved.  Buttaken step by step, they will provide a system check that will give youthe peace of mind of knowing that the fan will indeed work when needed.A properly operating electric fan provides a certain degree of protection.It helps keep high cooling system temperatures under control whether thecause is related to extreme operating conditions or other weaknesses inthe cooling system. Knowing the system is operating as it is designed isthe objective of this exercise.

DISCLAIMER: If while following theseprocedures, you cause damage to equipment or personnel, it's your faultnot ours. They work, we've tried it. But we can't control what you do,so be careful.