# Coolant Temp. Switch



## nelam (Feb 16, 2005)

Do you guys know how to test the coolant temperature switch at the thermostat housing on a '89 GA16i? I know, you can measure the resistance on the connector, with the engine is warm...etc. What is the normal resistance range?

My car has the tendency to run hot, and I am suspecting the switch is faulty that doesn't allow the fan to turn on. I tested the fan, and it is fine. And the car has a new waterpump, thermostat, 50/50 coolant....etc. 

And do you know where is the coolant temp. sender for the gauge is? I am trying to location it, and test to see if it is giving out wrong readings.

Thanks,
Nelson


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## bob89sentra (Sep 15, 2005)

I don't have the exact numbers for the fan switch, but it is just a temp switch so it should read open (no connection) when cold, and closed 1-10 OHMs when hot. The sender for your gauge is located on the back of your intake manifold under the throttle body. It is hard to get to, and takes a 12mm wrench to remove and only has one wire coming off it. The sensor on the side of the intake manifold above the water pump with two wires is for the ECU.


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## nelam (Feb 16, 2005)

How often do they go bad? I hardly hear them go bad.


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## bob89sentra (Sep 15, 2005)

On the Radiator fan temp sensor I have seen them go bad in one way. The wires that come out of the sensor get brittle and break off. 
Did you have overheating problems before you replaced your water pump and thermostat? It might be that you have a plug in the system, or an air bubble. Did you bleed the system after you installed the new parts?


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## nelam (Feb 16, 2005)

I wouldn't call it as overheating yet. But the temperature gauge occassionally reaches pretty high... so the engine is running hot. So I replaced the waterpump since it was leaking along with those three major coolant hoses, and bleeded the system properly. Now, the engine is running hotter than before... it is almost at the overheat range when idling, and the fan never kick in. So I jumped the connection with a wire at the coolant temp. switch, the fans kicks in. So I suspect the coolant temp. switch is not working properly. 

But for some reason, that still cannot explain to me why the car will overheat cruising on the freeway, since the fan is not needed at freeway speed. 

Maybe my coolant temp. sender for the gauge is malfunctioning as well. or my radiator is clog along with a bad coolant temp. switch, or the voltage stablizer for the gauge cluster is bad....

Thanks,
Nelson


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## bob89sentra (Sep 15, 2005)

nelam said:


> I wouldn't call it as overheating yet. But the temperature gauge occassionally reaches pretty high... so the engine is running hot. So I replaced the waterpump since it was leaking along with those three major coolant hoses, and bleeded the system properly. Now, the engine is running hotter than before... it is almost at the overheat range when idling, and the fan never kick in. So I jumped the connection with a wire at the coolant temp. switch, the fans kicks in. So I suspect the coolant temp. switch is not working properly.
> 
> But for some reason, that still cannot explain to me why the car will overheat cruising on the freeway, since the fan is not needed at freeway speed.
> 
> ...


I had the same overheating problem. It started running hot after replacing the water pump, and the only way I could get it to run the right temp was to drill a .100" hole in the thermostat. I even replaced the heater core and the radiator but it did not help. I suspect that the new water pump I put in does not supply enough flow at low rpms, because it would cool off if I run at 4,000 RPM, but even on the coldist day it would run hot at 45-75 MPH if I run it at a lower RPM. I hope you do not have the same problem as I did, because It is a pain.
Bob


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## 4pt9fiero (Jul 5, 2005)

What brand thermostat did you replace it with? If it was anything other than an Nissan original I would get rid of it. I had an overheating stint once (running warmer than normal - never really overheated) when I replaced with a Napa brand, then I drilled a small hole in it and the engine wouldn't heat up properly - replaced it with OEM and have never looked back.


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## bob89sentra (Sep 15, 2005)

4pt9fiero said:


> What brand thermostat did you replace it with? If it was anything other than an Nissan original I would get rid of it. I had an overheating stint once (running warmer than normal - never really overheated) when I replaced with a Napa brand, then I drilled a small hole in it and the engine wouldn't heat up properly - replaced it with OEM and have never looked back.


I always use Nissan thermostats. I replaced my waterpump this weekend with the Nissan part, and I no longer have problems with overheating. On closer inspection I ran the NPW (the new pump I put in a few years ago) with out a thermostat, and at RPM's between idle and 3K RPM I would get almoast no flow, untill I hit about 4K RPM. The nissan one I put in this weekend has the same flow at idle as the NPW pump has at 4,000 RPM. No more running hot for me


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