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Discussion Starter #1
There have been some posts on when the radiator fan turns on, and the fact that there is only 10 -20 degrees (F) between that temp and engine damage.

Here is how to lower the point at which the cooling fan turns on.

According to the chart I have, cooling fan turns on at 103 C (217.4 F), 177 ohms, .382 volts.

You need to lower the resistance, so the ECU thinks is its hotter than it actually is. Around 105 C (221 F) 168 ohms, .364 volts)

This will kick the fan on earlier...

Formula: Resistance Total = Resistance 1 X Resistance 2 divided by Resistance 1 + Resistance 2

Rt= R1 X R2
R1 + R2

Rt (168) = 177 X R2 / 177 + R2

If R2 = 2200 ohms, then Rt = 163.8199 (106 C)
If R2 = 3300 ohms, then Rt = 167.9896 (105 C)
If R2 = 4700 ohms, then Rt = 170.57.63 (104 C)

Assuming that the sensor has a two wire connector on a pigtail, just short a 3.3K 1/4 watt resistor across the connector. It may be possible to do this at the ECU instead.

Can someone confirm that the coolant temp sensor has two wires and a connector?

Any comments / suggestions? :smartje.rd.zw:
 

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Matt, are you sure this is wise?
It would be one thing if this sensor only operated the fan, but it also affects the information being fed to the engine control unit which determines fuel amount to inject, timing etc. I'll let you experiment with yours first.
Let us know how things turn out. That is always good to hear.
 

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I can't confirm the sensor information... but I wonder if some parts (thermostat, sensor, etc) or programming have changed in the newer models? My '13 has never gone above 90 degrees C... even in the Florida heat. And the fan does come on.
 

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Don't think our 2011 has gone over 194 F (on the UltraGauge) even during the hottest part of this past summer. :)

...above 90 degrees C - what's that in old money? :D
 

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Discussion Starter #7 (Edited)
temps

Your raising the temp the car thinks the sensor is reporting by two degrees C.

In other words, if 103 C, the car thinks its 105 C.

With AC on, Ultragauge reports 190-205 F
With AC off, temp can get to 220 F before the fan is on.

As the AC turns the fan on continuously, and keeps the temp at 190-205 F,
I can't see how a fan turn on at 210 F (with no AC) hurts...

This does not affect the thermostat or engine operating temp...
 

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I've sat with the a.c. off in my cabrio while trying to search for a business on my cell phone. Engine temp rises dramatically while idling with no fan and parked. It made me nervous. I turned on the A.C. and cooled the engine down. :)
 

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Just so happens I did this test yesterday. I was concerned about overheating being the possible cause of the engine head failures and owned a car previously which turned on the fan at about 225F which I reprogrammed. I believe I posted on this subject previously.

First, with a/c on, fan runs virtually continuously, temps seem to run about 195-200. This is on a 2009. My assumption is it's equipped with about a 195 thermostat to create a floor.

With a/c off, my fan turned on at 212 and turned off when temperature reached 200. These coolant temps were measured with a new scangauge e.

It appears that with a properly functioning cooling system and reasonably prudent operation of the vehicle, the normal temp range will be 195-212. My conclusion is that this temperature range should not be the direct cause of any issues and no correction or modification is necessary.
 

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Sounds like a lot of work to correct a problem that does not exist.

If the engine overheats something is wrong. To which the corollary is, if nothing is wrong the engine will not overheat.

If there is a coolant loss the engine may overheat and your modification will not matter. If anything in the fan control circuit including the fan itself fails, your modification will not matter.

Alteration of the coolant temperature sensor output voltage will also alter the fuel map modification for engine temperature. The system will self-correct if it stays in closed loop operation.

If it makes you feel better, do it and report, including any change in fuel trims.
 

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Here's my results from yesterday's evening commute:

30 minutes of driving, AC off, bumper-to-bumper, stop-and-go traffic averaging 15 mph, ambient temp: 89 F

My coolant temp would reach as high as 194 F, the fan would turn on, the temp would drop to 185 F, and the fan would turn off. After warm-up, the temperature stayed in the 185 - 194 range the entire time.

:smartje.zw.zw:
 

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I'd say either smart made a running change to cooling programming, or that the car hasn't aged enough to develop oddities in cooling (ex: coolant bubbles)...
 

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There have been some posts on when the radiator fan turns on, and the fact that there is only 10 -20 degrees (F) between that temp and engine damage.

Here is how to lower the point at which the cooling fan turns on.

According to the chart I have, cooling fan turns on at 103 C (217.4 F), 177 ohms, .382 volts.

You need to lower the resistance, so the ECU thinks is its hotter than it actually is. Around 105 C (221 F) 168 ohms, .364 volts)

This will kick the fan on earlier...

Formula: Resistance Total = Resistance 1 X Resistance 2 divided by Resistance 1 + Resistance 2

Rt= R1 X R2
R1 + R2

Rt (168) = 177 X R2 / 177 + R2

If R2 = 2200 ohms, then Rt = 163.8199 (106 C)
If R2 = 3300 ohms, then Rt = 167.9896 (105 C)
If R2 = 4700 ohms, then Rt = 170.57.63 (104 C)

Assuming that the sensor has a two wire connector on a pigtail, just short a 3.3K 1/4 watt resistor across the connector. It may be possible to do this at the ECU instead.

Can someone confirm that the coolant temp sensor has two wires and a connector?

Any comments / suggestions? :smartje.rd.zw:
Mattwithcats,
Take into consideration that the temp sending unit has a negative temperature coefficient meaning that its resistance is not linear with temperature change.

This is the actual resistance measurement from my temp sending unit when I characterized it in a controlled environmental chamber.

CTS Characteristics_3


CTS Characteristics chart

As you can see at low temperatures, the resistance is very high and the ECM compensates the air and fuel mixture to compensate for those temperatures. Placing a resistor across the sending unit for hot temperature conditions will effect the start up capability of the engine at very cold temperatures.
 

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Discussion Starter #17
Can you run that test again?

trfellows,

Can you short a 3300 or 3900 ohm resistor across the temp sensor and run that test again?

Many thanks,

If I only lower the temp two degrees C, it should have very little effect on the engine operation, I believe.

I have one to send you. $1.19 for five a Radio Shack...

I think Smart modified the ECU, exactly when is unknown, and changed the fan kick on point in the ECU,because some people are reporting lower temps with the AC off, and sitting still. Instead of 220 F, they are getting 212 temp to trigger fan kick on...
 

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trfellows,

Can you short a 3300 or 3900 ohm resistor across the temp sensor and run that test again?

Many thanks,

If I only lower the temp two degrees C, it should have very little effect on the engine operation, I believe.

I have one to send you. $1.19 for five a Radio Shack...

I think Smart modified the ECU, exactly when is unknown, and changed the fan kick on point in the ECU,because some people are reporting lower temps with the AC off, and sitting still. Instead of 220 F, they are getting 212 temp to trigger fan kick on...
I actually did a similar test when I was simulating the temp sending unit in the car. I had left the resistance set to 250 ohms (194 deg F) and let the car cool over night (75 deg F). The car would not start the next morning until I increased the resistance to match the temperature outside.

Essentually your trying to do the same thing by placing a 3900 ohm resistor across the temp sensor. At best, the ECM will never see the resistance increase above 3900 ohms so it will think the temp of the engine never drops below 50 deg F. Depending on the part of the country you're in, if the outside temp drops below 50 deg F then you'll have a hard time starting the car. If it gets really cold then the car won't start at all.
 

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Discussion Starter #19
out of ideas...

Other than a switch for winter operation (to take the resistor out of the wiring)

I am out of ideas.

Anyone else know how to change the fan kick on point?

Perhaps make it run continuously?

Mine is getting to 220 F temp max, and that's only ten degrees before the engine melts...

AC off and sitting in traffic...
 

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Other than a switch for winter operation (to take the resistor out of the wiring)

I am out of ideas.

Anyone else know how to change the fan kick on point?

Perhaps make it run continuously?

Mine is getting to 220 F temp max, and that's only ten degrees before the engine melts...

AC off and sitting in traffic...

A switched / fused circuit direct to the battery :rolleyes:


chief ...... not and electrical engineer :D
 
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