Radiator Fan activation temperature
 

I was curious if anyone knows if there is an OEM document out on the interweb or a website with information concerning the radiator fan activation temperature? If not could using an led in series with the radiator fan relay work to determine activation temperature?

It varies from vehicle to vehicle. Yes you can, it's extremely easy.

what value resistor do you place upstream of the led is my question then, or is the draw so small that you do not have to worry about the led exploding? Also would I have to use a scangauge to get the exact temperature of activation?

Not sure about the resistor and yea, an ultragauge is also an option at 1/2 the price, I have a UG and I prefer it over the SG personally.

If you have a SG you can tell when the fan is running by watching the engine temp. Engine gets hot> fan comes on> temp back to normal. The fans come on on both my Fiat and Renault at 93*C, if the temp is below that, I know the fan's not running. It basically never runs.

I was kinda bummed for that exact reason that my car does not have the digital option for coolant on the DIC :/

I'm guessing it's somewhere around 210-220. Factory stat should be 190 so the manufacturers give the fans a little time before cycling on; turning on at 200 would have your fan running constantly.

On my car (06 GP 3800 Series III L26. ) the operating temperature range 194 to 225. The cooling fans with the air off won't come on until the temp reaches 220 degrees then turn back off at 197 degrees via the u gauge. So the below information seems accurate for the 3.1L or 3.4L V-6 Engine (VINs J, E - RPOs LG8, LA1)

Engine temperature - Car Forums and Automotive Chat

I believe the factory thermostat is 195

1998-2004 LH cars (intrepid, lhs, concorde, 300m) fans came on low between 216 and 223 depending on a/c usage and engine size.

The temperature sensors on act as thermoresistors do they not? If so wouldn't it be possible to used the resistance value or voltage drop across the coolant temperature sensor to figure when the relay for the radiator fan will open?

You can measure the voltage from the CTS that the ECU reads. It will be a nominally 0-5V signal wrt ground/earth.

If you want, you can calibrate sensor voltage against an actual temperature with the sensor removed from the engine or a junkyard sensor. Put it in water brought to the boil or cooling from boiling, with a thermometer to read the actual temperature. Then plot the temps with the corresponding voltage.

The sensor will need the ~5V reference, a resistor or two (see below) and ground to complete the circuit, but it doesn't have to be connected to the car. A USB from "12V" adaptor should work to provide the reference 5V voltage. I have bought cheap Chinese USB cables for $4 that are suitable to cut and make the connections to the sensor. I would not use a USB voltage sourced from a PC or similar device (in the interests of the device).

The caveat is that GM (usually) includes two pull up resistors inside the ECU in series with the CTS resistance. Two resistances - rather than one - are used to increase the resolution of the sensor by creating two V vs T curves/ramps. Above a particular temperature - about 50C - one of the resistors in the ECU is bypassed (a transistor is switched in the ECU to short around it).

When the sensor voltage is read with the sensor in the car, the two voltage vs temp. ramps/curves are: one for low temps, with the additional resistance, and one for higher temps, without the additional resistance. You should only be interested in the higher temps so don't really need the additional resistance other than to be aware of its existence.

In the GM ECUs for which I have info. the always-in-series resistance is 350 Ohms with the sometimes-in-series resistance being 4k Ohms. Those values may differ in other ECUs with other CTS. Measure the voltage between the "350" Ohm and CTS sensor resistances and ground. (You are doing this anyway if you measure the voltage signal in the car.)

If you do want to measure the voltage as seen in the car, you can use jumper wires to extend the wires at the CTS connector to reach the sensor that you are placing in the heating or cooling water. With the ignition keyed on the CTS voltage will be present and reflect the temp. of the sensor.

If the aim is to provide a visual indication of when the cooling fan or fans is or are active then the LED (OP) can be made to work.

It can be in parallel with either the switched or switching side of the relay that switches the fan you wish to monitor.

It does need a current limiting resistor in series with the LED. The value of the resistor depends on the particular LED you are using and its characteristics. A typical red LED might drop 2V across it and need to be limited to 30 milliAmps max. continuous current. Assuming that it will be fed from 14V (running car - charging alternator).

The resistor needs to drop:

14V-2V = 12V

Using V = I x R:

12 = 0.030 x R

Solve for R:

R = 400 Ohms.

So use 430 or 470 Ohms.

What would you recommend for the voltage source? I might be able to get my hands on a DC power supply but there are no guarantees on that one. Any other ideas would be appreciated.

Watching my UG on the Acura, the cooling fan kicks on at 215 F, and stays on until temps drop to 195 F. The thermostat keeps temps around 188 F for the most part.

Why not just put a small current 12v bulb in parallel with the fan motor? Why make it complicated?

That will tell you when the fan turns on and then a look at the scan gauge, if set to measure coolant temp, will tell you the temp that the fan is activated.

A USB phone charger outputs 5V.


Go here for pin layout.
https://en.wikipedia.org/wiki/USB

does anyone know how well a "cylindrical radiator would work? Basically what i'm asking is if i got a couple different sizes of aluminium pipe from say 6-8"
all the way down to say 1.5"(being the size of the coolant line out of the radiator) pipe in 1" increments and put them inside one another, running a channel around them in a spiral front to back with added fins for cooling. would it give more cooling then the radiator or no?? i'm thinking that by cooling the coolant to a lower temperature can give far better temperature control then what they have now. I've measure a temperature difference of only about 30-40 degrees from the in to the out(and the coolant is only in the radiator for about 24") of a radiator on my jeep, so i'm thinking if you could double that it would be better.

so to summarize i'm talking about trying to run the area of a 1.5" pipe around 4-5 other pipes in order to increase the coolants over all time in the "radiator" from 24" to as high as 6-8' or more.

Unfortunately I do not have a scan gauge yet :/ The activation temperature light for me right now until I do purchase a scan gauge is just to be used as a reference to make sure my fan is not running, moreover to gauge how much grill block I can get away with. Judging by how cold it is currently I may be able to get away with a partial upper block.

Do you have a non-apple smart phone? The torque app and a bluetooth OBDII dongle can get you started with data acquisition for less than $20...

I was just looking at the wireless connectors for the OBDII, it looks like I may pursue that route.

It would provide more cooling capacity, but I'm unsure how much. Stock radiators already have a heck of a lot of surface area, so I'd be doubtful that increasing the run length would improve cooling efficiency by much.

The #1 thing you can do to increase cooling efficiency is to seal the gap between the grill opening and the front of the radiator. There is usually a good 1" or more gap between grill opening and the cooling fins, so air is allowed to move around the radiator instead of through it.

I tend to think the gap exists on purpose. If the grill were to get completely blocked, perhaps due to snow, the fans would still be able to pull air through the radiator, albeit much less efficiently. If you seal the gap, the fans must draw air through the grill opening.

Anything that results in a regulated 5V will work. At various times I have used: the USB adaptor, both wall plug and cigarette lighter ("12V") powered; a superfluous non-USB phone charger with the tip modified, wall plug powered; a bespoke, "12V" powered, 7805 based regulator circuit on perf. board with noise filtering (a web search will bring up any number of schematics for these); a spare ECU with just the power (plural) and ground wires connected, using one of the 5V reference outputs.

"12V" came from a car cigarette lighter, an SLA battery or a DC bench power supply.

You do need to be careful with the polarity with all of them.

Careful with incandescent bulbs as they can draw a significant amount of current. On the fan side of the relay it is probably a tolerable fraction of the motor current. An LED (and resistor) is just as easy and will draw only a tiny amount of current, definitely a negligible current relative to the fan. (Don't even consider an incandescent bulb on the switching side of the relay.)

When doing this to measure the actual voltage corresponding to the temperature I would just measure the voltage drop across the sensor correct?

Also shouldn't I just use coolant and apply heat to it since water boils at 212F. If the fan activation temp is above that then I would only have reference voltages up to 212F.

This whole thread could be answered with a $9 ELM237 OBDII bluetooth adapter and a free app called Torque.

You can then read the temps directly and see when the cooling fans turn on.

There are more expensive and complicated ways to keep tabs on things, but this would be the cheapest/easiest/most accurate way.

Yep. Also, check (measure) the reference voltage in the car and what you are using match. The reference voltage is what is across the CTS connector with the sensor disconnected.

The sensor voltage is pretty linear wrt temp. The activation temp. for the first fan speed won't be much above 100c (212F) anyway. You can extrapolate the little bit of temp. that is above (the voltage should be lower) on your plot.

Maybe. I could do the voltage testing at $0.00, out of the parts box. Without that parts box, ^ probably is the better way.

I was just looking at the fuse block and there are; 2 cooling fan K3 micro relays, 1 u-micro relay K7, 2 HC- cooling fan relays one is K2 and K1. I'm unsure what the K #s stand for anyone know? Also i'm unsure what the U, and HC prefix for the relays are.

Okay so I have done some digging around and it seems that HC stands for high current. I'm figuring that those two relays must have something to do with the fans speed and so only open when the fan must spin faster as they can allow up to 120A based upon the rating from what I have read. I'm still unsure of what the "U" relay does for the cooling fan. There is also two general "micro relays" and then there is the matter of the K1, K2, K3, and K7 delineations as well. So figuring in i want to prevent the fan from coming on at all I would want to target the relay that controls the lowest fan speed. Now I just need to figure out which one of them controls it right?