[calzplace]

Hi everyone,

I've been reading through the various posts about troubleshooting cooling fans, and I think I'm stuck.

I haven't done any (recent) modifications to my 2007 Mustang GT that involve the cooling system or PCM. I did an SCT tune many years ago, so my low speed fan kicks in at 180F, and my high speed threshold kicks in at 190F. A couple weeks ago I ran it pretty hard in an autocross race, but didn't have any problems then.

Now yesterday, just normal around town driving, it overheated and started blowing antifreeze out.

When I let it cool down, and turn the AC on Max and the blower fan on 4, the fan kicks in. But if I let the motor warm up past 190F the cooling fan turns back off, even if I have the AC on. (I'm using the Torque app to monitor temps over OBD-II)

If I let it cool down, and then run it at idle and watch the temps, the fan kicks on at 180F, and then stops when it hits 190F.

I checked fuse #3 (40 amp) for continuity, and it was fine. I even swapped it around with another 40A fuse just to make sure.

I then swapped relay #25 (high speed) with the low speed relay #28, and still no change. Just to make sure, I swapped it with the Horn relay which was the same type. I also wire brushed the relay posts, but they were pretty clean looking anyway.

I then unplugged the harness from the fan, and hotwired the fan to the battery. It seems to run just fine with 12v applied to it.

I then stuck my multimeter in the harness and repeated the test. At 180F I was reading about 13v at the harness. When my temp hit 190F the voltage dropped down to 2.0v.

This seems to correlate with my observations too -- I noticed one time when I turned the AC on, the fan sort of twitched and rotated a little bit, and stopped.

Any advice on what would cause this? Am I right in thinking that something is wrong on the high speed part of the PCM circuit if I see only 2v at the harness? What else can I check?

Thank you!

--Cal

 

[night rider]

Hi calzplace. This wiring diagram might help you.

 

[marylandGT]

There's a relay that's mounted on/in the fan shroud at the plug. This is usually the culprit with most fan problems on the 05-09s.
Your symptoms are almost exact to what I had.

 

[calzplace]

Thanks @marylandGT.

Is this the plug you're talking about:

The red/black pair go straight to the fan motor, and the 4 wires on the other side appear to be 2 ground, and 2 green/yellow stripe that go out to the fuse box.

If that's the right plug... it seems weird that there's a relay in there. I was just assuming they doubled up the wires to handle a max load of 40 amps.

Is it possible to just buy that relay without buying a whole new fan + shroud assembly?

Thank you!

--Cal

 

[calzplace]

Hmm, looking through @night rider's schematic... it looks like I was mistaken on the colors. light green/violet for high speed, light green/yellow for low speed. And since "engine cooling fan motor" is all wrapped up in a magic box, it seems unlikely I could replace whatever burned out inside that plug.

But, I should at least measure the voltage from the light green/violet and light green/yellow wires to confirm that it isn't a problem further back in the circuit. It just seems weird that I measured 13v for low speed at the red/black wires that plug onto the motor. Then 2v for high speed. I would think it should be the other way around. 13v for high speed, and somewhere around 6-10v for low speed? I suppose my testing method could have been wrong too.

 

[marylandGT]

Yes, that's it in the picture. It's under the overflow reservoir. Mine overheated so much, the plugs melted together.
Go to the 05-10 Tech section and type "cooling fan" in the search function. There's a thread, third one down titled "running hot. Fan only comes on when ac is on".
This thread will explain, what I believe is your problem, better than I can.

Hope this helps.

 

[marylandGT]

Is it possible to just buy that relay without buying a whole new fan + shroud assembly?

Thank you!

--Cal

Yes, the original poster in the other thread had to go through a dealer for it. I think it was $70

 

[calzplace]

PROBLEM SOLVED! :thumbsup3.gif:

Check this out:

These are the solderless press-fit connectors underneath the fuse box breadboard. The burned out one is for the green/violet wire connecting to the high speed fan relay pin #30.

It's pretty poor engineering I say! The 40A fuse should have blown before the circuit connections melted like this. The metal connector was actually fused into the melted plastic. Luckily it was on the corner, and I cut out the 2 sides of the plastic corner with my dremel tool.

I soldered on a 12GA jumper wire directly to the pin underneath the fuse breadboard. Then I just ran that through my newly opened space and soldered the jumper onto the green/violet wire.

I tested both low and high speeds with the car idling, and everything works perfectly!

But I hope this doesn't happen again and that my solder joints hold.

I was also thinking of maybe changing the fuse to a 30A in order to save the rest of the circuit if it overloads again. Any suggestions on that?

Thank you!

 

[night rider]

Way to Go ! and good to know.

 

[Bullitt95]

PROBLEM SOLVED! :thumbsup3.gif:

Check this out: View attachment 465250

These are the solderless press-fit connectors underneath the fuse box breadboard. The burned out one is for the green/violet wire connecting to the high speed fan relay pin #30.

Great job finding and fixing the problem.
Did you recently have the engine cleaned? Just wondering whether a drop of water might have found its way into the relay box and shorted out the contact.

 

[calzplace]

Did you recently have the engine cleaned?

No, not really. The only thing different I did was a 2-day long autocross race. But that's not too hard on the car either. You run it hard for 50 seconds, and then it cools down for 10 minutes waiting in line.

It did rain when I was driving it recently too, but I doubt any water got into the fuse box. The inside of the box looked very clean other than the burned contact.

 

[marylandGT]

That IS good to know. I'm sure you won't be the last one to post with this problem. Lol

 

[c0op3r]

I have written a HOW TO on fixing this problem, it was easiest to host it on my Server here is the link:

http://www.c0op3r.com/images/Harley/Fan%20Relay%20Replacement/How%20to%20repair%20ford%20fan%20relays%202005%20through%202010%20mustang.htm

The short of it is that I replaced the Ford Relays with Bosch 30 Amp Relays

 

[Kempz]

Thanks for sharing the solution to your problem! I am currently experiencing the same issue, and after replacing several parts, have been at a loss. Glad to see someone actually figured out the problem.

 

[calzplace]

Small update, the cooling fan stopped working exactly one year after the fuse box short happened. I upgraded to the Ford Racing GT500 cooling fan, part number M-8C607-MSVT. It seems quieter than the stock fan, and based on the blade configuration, looks like it should pull a little more air with less drag on the motor.

My guess is that the motor started to drag on my stock fan, which caused it to draw more current from the circuit and melt the wiring. It still isn't an excuse for a 40A circuit using such tiny connectors.

But hopefully this provides everyone a solid background to the whole cause of the problem.

 

[moazmohamed54]

Thx all, thx for contributing.
To update the case, adter some diagnostics, figured that the connection/bridge between wires (that one coming from fan motor and the wire from over-fan port) damaged by some heats, so the bridge was connecting them together melted with the black tapes were covering them.
So, this thing caused failure in the flow of current, and the fan stopped.
I disconnected them, cleaned the black plastic on the non-covered parts of the wire, reconnected them properly with good isolation and it worked fine.