What causes cooling fans to come on too early?

[72Z/28]

I am wondering about this issue about my radiator cooling fans that come on way too early before the engine reaches operating temperature.

there are two wires from PCM for each fan ( one dark blue and dark green)connected to relays.

When I start the engine, fan no 1 comes on a few minutes after engine start up. Upper radiator hose when fan no 1 comes on is around 118 degree F ( using infrared temp gun). The second fan comes on within a few minutes as well when the temperature at upper radiator hose is around 125 degrees F.

Once both fans are on, they keep running.

Will appreciate your input guys on how to address the issue.

When I took my car to a tuner. He said that it did show on the PC that the fans are controlled by the PCM.

I am not sure if he had checked properly or not.

Then, what else could cause the fans to come on at different time intervals and keep running all the time once they are on

[andre68]

Just to knock out the obvious, are you certain the coolant level is perfect and there is no air in the system? Probably the 2 most common issues that trigger cooling system problems.

The tuner should be able to tell you what temp the fans come on, if its controlled by the ECU.

[72Z/28]

Just to knock out the obvious, are you certain the coolant level is perfect and there is no air in the system? Probably the 2 most common issues that trigger cooling system problems.

The tuner should be able to tell you what temp the fans come on, if its controlled by the ECU.

The coolant level is perfect. I have done the radiator bleeding. I have noticed small bubbles but not to the extent that the coolant level drops ( like you see in some of the videos posted in youtube).


I have seen a video today showing how to get the air out of the cooling system by disconnecting the steam line from the engine side and blowing through the steam line until only coolant flows out of the steam line port at the engine.

So based on the way the fans are currently operating,does this mean that they are controlled by the ECU?

[andre68]

The way I verify that all air is out of the system is by starting the car cold with the radiator cap off. make sure the car is on level ground. Watch the coolant level closely. as the engine gets hotter, you will see the coolant rise (and any air bubbles pop). As soon as you see the coolant about to overflow the tank, screw the cap back on.

You have just pushed all the trapped air out of the system (assuming the radiator cap is the highest point in the system, which it should be). The method works for me every time, on all my cars. Some coolant will overflow when you thread the cap in, so have a towel ready.


You said the tuner saw the fans were controlled by the ECU? he saw this on his computer? If you want to verify, you need to look at the wires coming from the electric fans. Is it connected to the main wiring harness at all?

My BMW 540i has an electric fan setup that is completely independent of the factory wiring harness/ECU, as the car came from the factory with an engine driven fan (so the ECU was never programmed to control an electric fan). My electric setup has its own wiring harness, temperature sensor, and fuse. It comes on low speed when the temp reaches 91 c, and high speed when the temp reaches 99 c. No computers.

If your fan is run independently from your ECU, then you can swap out to a different temperature sensor to a higher temp rating (like I did) to change when the fans come on.
If you fan is controlled by the ECU, then you would need to change the on/off timing of the fans within the software.

The current way the fans are operating does not dictate whether or not it is controlled by the ECU.

[randy]

It will be in your tune. Do you have HP tuners?

[72Z/28]

The way I verify that all air is out of the system is by starting the car cold with the radiator cap off. make sure the car is on level ground. Watch the coolant level closely. as the engine gets hotter, you will see the coolant rise (and any air bubbles pop). As soon as you see the coolant about to overflow the tank, screw the cap back on.

You have just pushed all the trapped air out of the system (assuming the radiator cap is the highest point in the system, which it should be). The method works for me every time, on all my cars. Some coolant will overflow when you thread the cap in, so have a towel ready.


You said the tuner saw the fans were controlled by the ECU? he saw this on his computer? If you want to verify, you need to look at the wires coming from the electric fans. Is it connected to the main wiring harness at all?

My BMW 540i has an electric fan setup that is completely independent of the factory wiring harness/ECU, as the car came from the factory with an engine driven fan (so the ECU was never programmed to control an electric fan). My electric setup has its own wiring harness, temperature sensor, and fuse. It comes on low speed when the temp reaches 91 c, and high speed when the temp reaches 99 c. No computers.

If your fan is run independently from your ECU, then you can swap out to a different temperature sensor to a higher temp rating (like I did) to change when the fans come on.
If you fan is controlled by the ECU, then you would need to change the on/off timing of the fans within the software.

The current way the fans are operating does not dictate whether or not it is controlled by the ECU.

Thanks for the write up man. I am following the same method for bleeding the system. However, I do have an overflow tank, so when the coolant starts to rise, whatever is overflowing will end up going to the overflow tank.

I guess the tuner who did the the dyno tune was too lazy to check thoroughly or there is something is wrong.

I remember the two wires coming out of the ECU connectors are connected to the fans.

As you suggested, I did verify that just now and both wires ( Dark Green &Dark Blue) are coming out of the ECU and going to fan relays.

I am confused now, although the wires are connected from ECU to the relays, is there a possibility that the tuner could not recognize them in his software.

Unfortunately I do not have an HP tuner to double check that.

I also have a binary switch for my Vintage Air. As soon as I run the AC, one fan comes on regardless of the engine temp whether it has reached the operating temperature or not

[72Z/28]

It will be in your tune. Do you have HP tuners?

Unfortunately I do not have an HP tuner.

I am a bit confused he could not recognize the fan operating temperatures from the tune even though they are wired from the ECU.

[andre68]

Are you using an OEM ECU, or an aftermarket Holley, etc? I am not a tuner of LS engines, so I can't guide you on what scan tool/computer software to use. But I would invest in one so you can check things like this yourself. I can't speak for what your tuner saw on his software. I'd call him and confirm or find a new tuner....you need to see what temp the ECU is looking for when opening the fans. Seeing that you have an LS, the ECU will be relying on a temp sensor located on the driver side head. Unfortunately, an infrared gun on a hose will not match the temperature the ECU is seeing when it turns on your fans.

BTW, when you say overflow tank, do you mean an expansion tank (that has a pressurized cap?) or a recovery tank? (regular threaded cap)
My method will work wherever the pressurized cap is, whether its the radiator or expansion tank.

A recovery tank simply holds discharged coolant from the pressure relief when the coolant is expanding.....this tank will have a simple threaded cap (no pressure rating). If this is the tank you have.....you'll notice that the hose connecting to this tank will be connected to the filler neck of the pressurized cap (wherever that is....radiator or expansion tank). That hole is so close to the opening of the filler neck that the coolant will overflow the open filler neck wayy before it starts filling up the recovery tank.

Here is some info from canton racing: http://blog.cantonracingproducts.com/blog/setting_up_your_cooling_system_expansion_vs_recove ry

Assuming the recovery tank is at the correct level and sits above the pressurized cap, no air pockets will be trapped in there.

And just to knock out another obvious, check if your A/C is on (if you have it). The fans may come on sooner when the climate control is on.

[randy]

if you are located near dallas i could pull your tune file quick and tell you.

if you are using HP tuners or can get access its under systems, fans. Lots of fan options there. You dont need to buy credits to read the tune.

[72Z/28]

Are you using an OEM ECU, or an aftermarket Holley, etc? I am not a tuner of LS engines, so I can't guide you on what scan tool/computer software to use. But I would invest in one so you can check things like this yourself. I can't speak for what your tuner saw on his software. I'd call him and confirm or find a new tuner....you need to see what temp the ECU is looking for when opening the fans. Seeing that you have an LS, the ECU will be relying on a temp sensor located on the driver side head. Unfortunately, an infrared gun on a hose will not match the temperature the ECU is seeing when it turns on your fans.

BTW, when you say overflow tank, do you mean an expansion tank (that has a pressurized cap?) or a recovery tank? (regular threaded cap)
My method will work wherever the pressurized cap is, whether its the radiator or expansion tank.

A recovery tank simply holds discharged coolant from the pressure relief when the coolant is expanding.....this tank will have a simple threaded cap (no pressure rating). If this is the tank you have.....you'll notice that the hose connecting to this tank will be connected to the filler neck of the pressurized cap (wherever that is....radiator or expansion tank). That hole is so close to the opening of the filler neck that the coolant will overflow the open filler neck wayy before it starts filling up the recovery tank.

Here is some info from canton racing: http://blog.cantonracingproducts.com/blog/setting_up_your_cooling_system_expansion_vs_recove ry

Assuming the recovery tank is at the correct level and sits above the pressurized cap, no air pockets will be trapped in there.

And just to knock out another obvious, check if your A/C is on (if you have it). The fans may come on sooner when the climate control is on.

I have OEM ECU with blue and red connectors. Dark green wire (pin 42) and Dark Blue wire (pin 33). Both going from ECU or PCM to fan relays.

Both fans come on as soon as turn on the AC even with cold engine.

By the way, I have a recovery tank not the expansion tank

I have found so many threads in LS1Tech regarding wiring cooling fans and AC with binary or trinary switches. Unfortunately, I could not find a clear schematic that shows wiring trinary switches with dual fans and compressor.

I am just sick of going through the cooling fans wiring, relays as I have to trace all the crapy wiring done by the stupid electrician. This may require dropping the vintage air evaporator just to trace one stupid wire.

Just do not feel like doing this as I have recently rearranged the big mess on the dash wiring, and I still cannot figure out why the stupid tach and speedometer on classic instruments do not work.

[dhutton]

I have OEM ECU with blue and red connectors. Dark green wire (pin 42) and Dark Blue wire (pin 33). Both going from ECU or PCM to fan relays.

Both fans come on as soon as turn on the AC even with cold engine.

By the way, I have a recovery tank not the expansion tank

I have found so many threads in LS1Tech regarding wiring cooling fans and AC with binary or trinary switches. Unfortunately, I could not find a clear schematic that shows wiring trinary switches with dual fans and compressor.

I am just sick of going through the cooling fans wiring, relays as I have to trace all the crapy wiring done by the stupid electrician. This may require dropping the vintage air evaporator just to trace one stupid wire.

Just do not feel like doing this as I have recently rearranged the big mess on the dash wiring, and I still cannot figure out why the stupid tach and speedometer on classic instruments do not work.

At least one fan should come on when you turn on the AC if you are using a binary switch. It has nothing to do with the engine temperature.

Don

[randy]

located near dallas at all?

[72Z/28]

located near dallas at all?

Thanks Randy for the offer, well appreciated.
Unfortunately I do not live in the USA.

I have drown a rough schematic of cooling fans wiring along with compressor and Binary Switch.

I am going to share the link soon to my instagram, and hopefully someone could go through the schematic and correlate with how the fans are operating now based on information given in my previous posts