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1997 200SX base 5-speed
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41 Posts
Discussion Starter #1
I've noticed that after driving the car and coming to a stop, if sitting long enough to get hot enough for the fans to turn on, they do, but then they don't turn off. They turn off when the car is shut off and if I restart the car they are off again until heated back up. The temps go down but the fans continues to run. It gets so cold that the lower hose gets cool and the thermostat closes. Fan just keeps running. I replaced the relay suspecting that it's sticking, but same issue persists.

Unlike other fan issues I've experienced, this is only after the first cycle of the fans that it continues to run. Not like they are always on from a start up, or staying on once the car is shut off. There are no leaks and the rad/reservoir are full. New thermostat, radiator, cap, upper/lower hoses. What gives?
 

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1997 200SX base 5-speed
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41 Posts
Discussion Starter #2
I happened to look at the ECT data the other day. The car heats up to around 195*F before the fans come on, but the temps only go down to 192*F. Not cool enough to signal the fans to turn off. So I'm thinking 3 possibilities.

1 ECT sensor is faulty and gives a high reading.
2 Thermostat is the wrong temp. 180* is OEM. I replaced with and OEM but I did see on RockAuto that a 192* available. Maybe I received the wrong one.
3. The fans are weak and just can't pull enough air through the rad to cool it down.

I replaced the radiator with a Nissen's brand. This one is literally double the OEM width and should make the car way easier to cool off. So I'm not thinking the fans are likely the culprit. Although it was the fix on an old Eclipse I had. I guess the next thing to do is pull the thermostat out and do the boiling water and thermometer test.
 

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1997 200SX base 5-speed
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Discussion Starter #3
I shopped around for thermostats and realized that there are 3 temp ratings that are considered OE temps for these cars. 192 being one of them. They come in 170, 180, and 192. The car needs a 180 and is what I intended to put in it when I did it. I never looked at what it was, just ordered one and put it in not knowing they could be any of three temps. So I'm 99% sure I'm running a 192* thermostat. The data from the ECT sensor validates this. For those in emissions required states, you need a 180* because 170* is too low to burn off emissions correctly and can fail smog/ dirty up catalytic converters. ]

The 192* will pass smog fine, but the downfall to this is that the fans run too much. This is unnecessary wear and tear on the fans leading to failure sooner. And in such a small engine vehicle, it's noticeable how much power is robbed while loads are on. Makes for slower and sluggish performance, and equated to less fuel economy as well.

I ordered a 180* and will post results once installed.
 

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1997 200SX base 5-speed
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41 Posts
Discussion Starter #4
Well pretty unbelievable, but after installing a 180* thermostat, the car is experiencing the same behavior with the fans and temps. So I probably had the correct one in already, but at least it's is verified to be 180* now and it's a cheap part. I think I will throw an ECT sensor at it next as it is just the next logical and most common part to start to fail. Just this silly little issue is all that I'm having with the car and as a technician it's driving me crazy. When coolant temp sensors get old and start to fail they can send false information. So now I'm thinking that the ECT sensor is telling the computer that the coolant is hotter than it is, thus the fans stay on. The air coming off the radiator from the fans is not what I'd call hot at all, so I think it's running pretty cool. So ordering the temp sensor now and will update again after testing.
 

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I've noticed that after driving the car and coming to a stop, if sitting long enough to get hot enough for the fans to turn on, they do, but then they don't turn off. They turn off when the car is shut off and if I restart the car they are off again until heated back up. The temps go down but the fans continues to run. It gets so cold that the lower hose gets cool and the thermostat closes. Fan just keeps running. I replaced the relay suspecting that it's sticking, but same issue persists.

Unlike other fan issues I've experienced, this is only after the first cycle of the fans that it continues to run. Not like they are always on from a start up, or staying on once the car is shut off. There are no leaks and the rad/reservoir are full. New thermostat, radiator, cap, upper/lower hoses. What gives?
Are you having overheating problems? Here's a chart showing when fans run/stop, I hope this helps:

101880
 

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1997 200SX base 5-speed
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41 Posts
Discussion Starter #6
No overheating. Just fans that don't turn off once they've turned on. It's something stupid, just haven't figured it out yet. Thanks for the chart, though it is for an A/T and I have an M/T. Might still come in handy.
 
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