420A 2g GS 420A radiator fans won’t turn on.

[96WhiteEclipse]

Hey guys, my 2g GS has recently been overheating only at idle. The radiator fans work because when I turn the AC they kick on but when I’m sitting at idle there’s nothing then it begins to overheat. I’ve replaced my water pump 4,000 miles ago when I did my timing job and just replaced the sender, sensor, and thermostat as well flushing the cooling system (which got a lot of junk out) but my problem still persists. I then took both hi and low relays out and cleaned off the prongs to see if there was a bad relay. The fans now kick on but not until the car reaches a little too hot for comfort.

The picture of the temperature gauge is the moment the fans kicked on. And the second is where the gauge sits at idle. Both fans turn on when the AC is on but when the AC is turned off the fans doesn’t kick on until the first pic.

Any ideas? Fans only seem to be running at one speed when they kick on.

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[petrosian]

Did you check/replace the sensor in the radiator? There is a temperature sensor in the radiator that controls when the radiator cooling fan comes on.

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[petrosian]

Apologies. Sometimes I forget we’re talking about 2G’s

In your case, the fan relay signal comes from the ECU (PCM). The engine coolant temperature sensor tells the ECU what coolant temp is, and the ECU triggers the fan relay(s).

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[96WhiteEclipse]

Did you check/replace the sensor in the radiator? There is a temperature sensor in the radiator that controls when the radiator cooling fan comes on.

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I can’t seem to find a part that matches that description/ location. Do you know the part number?

 

[Sirius1995]

Bad coolan temp. sensor, this is really common issue on 420a and cheap and easy to fix

 

[BLACK'98DSM]

There are 2 coolant temperature sensors on the 420a. The one you should be worried about is the larger one. It sends the signal to ECU. The smaller sensor is only for gauge reading, which you say is functional.

(Yes, I have a 420a water neck hanging on the wall. Don't ask why, because I really don't know myself.)

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[96WhiteEclipse]

Hey guys, my 1996 Eclipse GS with the 420A motor coolant fans still won’t kick on their own causing it to over heat. When the AC is on both fans will run. However, when the AC is NOT on the cooling fans will not turn on on their own. I replaced the coolant temperature sensor and sending unit which did not solve my problem. It only starts to overheat when sitting at idle/ in traffic for too long. What’s interesting to me however is that when I disconnect the coolant temperature sensor the check engine light illuminates and both fans turn on.

What could be the issue here? Could the new part be bad?

 

[luv2rallye]

Unplug the 2 wire CTS (green-white and black-green wires). Now short those 2 wires together in the harness and run the engine. If fans don't come on your CTS is most likely bad (since it is suppose to supply near 0 resistance with high temps).

 

[96WhiteEclipse]

Unplug the 2 wire CTS (green-white and black-green wires). Now short those 2 wires together in the harness and run the engine. If fans don't come on your CTS is most likely bad (since it is suppose to supply near 0 resistance with high temps).

Shorted the harness and fans still kick on.

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[96WhiteEclipse]

There are 2 coolant temperature sensors on the 420a. The one you should be worried about is the larger one. It sends the signal to ECU. The smaller sensor is only for gauge reading, which you say is functional.

(Yes, I have a 420a water neck hanging on the wall. Don't ask why, because I really don't know myself.)

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Replaced coolant temp sensor and issue still persists. When the sensor is unplugged the check engine light illuminates and both fans kick on high.

 

[96WhiteEclipse]

Unplug the 2 wire CTS (green-white and black-green wires). Now short those 2 wires together in the harness and run the engine. If fans don't come on your CTS is most likely bad (since it is suppose to supply near 0 resistance with high temps).

I shorted the harness out and the fans came on. What could this mean?

 

[luv2rallye]

Oops. Looks like I said it backwards. Shorting those two wires in the CTS harness should force the fans on - which proves the fans, wiring, fan relays, and PCM are working. It doesn't prove whether the CTS sensor is good/bad. However when the engine gets hot, the CTS sensor's resistance should go near zero (assuming there's enough water in the cooling system to touch it) and so it should turn the fans on. So either your sensor is bad, it's wires are broken, or your cooling system is not full.

 

[96WhiteEclipse]

Oops. Looks like I said it backwards. Shorting those two wires in the CTS harness should force the fans on - which proves the fans, wiring, fan relays, and PCM are working. It doesn't prove whether the CTS sensor is good/bad. However when the engine gets hot, the CTS sensor's resistance should go near zero (assuming there's enough water in the cooling system to touch it) and so it should turn the fans on. So either your sensor is bad, it's wires are broken, or your cooling system is not full.

Well funny enough, I decided to check the connector and clean it and make sure there was a good connection. After that the fans finally began to turn on without the ac being turned on. However, the fan doesn’t kick on until the car starts to overheat. This is the point the fan turned on. Should I be concerned or leave it be?

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[luv2rallye]

Leave it.

 

[96WhiteEclipse]

Leave it.

It wouldn’t cause much damage to my head gasket right?

 

[luv2rallye]

If the temp gauge is only in the middle as shown in post 6 when you say it's overheating, that's normal. If it's pegged that's a different story.

If concerned, when cool (to not burn yourself), remove thermostat and run some radiator flush cleaner thru the system (follow can directions running for 15 min) and then after cooling down remove lower main rad hose and reverse flush the system (shoot backwards up thru rad and up hose) with a garden hose pressure.

Test if thermostat opens in a pan of boiling water at 195*F or just buy a new one. [Can also get a thermostat that opens at a lower temp if you need (but then you may not get enough heat in winter, although in Oklahoma you probably don't care) although 195* should work anywhere if the rest of the system is working properly.]

Put back together - make sure system is burped of trapped air by squeezing lower hose with cap off. If still overheating you may need a new radiator (they don't last forever).

 

[pauleyman]

Get an obd scanner and see what it says coolant temp is. The coolant temp sensor is cheap if you choose to just replace it.

 

[96WhiteEclipse]

If the temp gauge is only in the middle as shown in post 6 when you say it's overheating, that's normal. If it's pegged that's a different story. If concerned, when cool (to not burn yourself), remove thermostat and run some radiator flush cleaner thru the system (follow can directions running for 15 min) and then after cooling down remove lower main rad hose and reverse flush the system (shoot backwards up thru rad and up hose) with a garden hose pressure. Test if thermostat opens in a pan of boiling water at 195*F or just buy a new one. [Can also get a thermostat that opens at a lower temp if you need (but then you may not get enough heat in winter, although in Oklahoma you probably don't care) although 195* should work anywhere if the rest of the system is working properly.] Put back together - make sure system is burped of trapped air by squeezing lower hose with cap off. If still overheating you may need a new radiator (they don't last forever).

The gauge will stay right in the middle for a bit, then creep up before the fan kicks on. That is normal?

 

[99dsmer4g63]

He means the ECT sensor for the ECU not the gauge. There is two sensors on the thermostat housing. Make sure there is no air in the coolant system as this will make the gauge appear erratic at times too.

-Daniel