Working on an overheating issue on my 2008 Mustang GT. Car starts normally after sitting all night and fan starts up when I click on the AC. Let the car run (or drive it in traffic) and as soon as the needle gets to normal the fan shuts down. this of course causes the radiator to start heating up shutting down my AC before going in the RED. I immediately turn on the heater with fans on high and temp starts retreat towards normal. 3 fans later it is doing the same thing. Took it to the local mechanic and the computer says all systems are green and all circuits are good. Hoping someone who has solved this problem can help.

Need to mention. The mechanic also checked the low and high speed relays as well as the fuses. all good.

So here is the latest: Took it to a local mechanic recommended by a trusted mechanic who raved that this guy was a "Mustang Specialist". Of course the problem could not be replicated. I tried for an hour and this thing would not perform as described above. Drove away and the car shuts down abruptly 2 miles down the road but not due to overheating. Got it restarted and back to the specialist. He hooks up a computer and takes it for a 30 minute ride. Comes back and says he cleaned the Air Flow sensor and the throttle body because they were both filthy. Meanwhile no sign of an overheat condition. The car now has more jump from the light and idles smoother. I'm waiting for the next 90 degree day before i call it a complete success but so far, so good as there is no hint of overheating. More update later.

Cleaning the air flow sensor and the throttle body did improve idle and overall performance but as soon as the cold front left and the weather got hot the problem with the fan stopping at high temp returned. Back to the mechanic!

  • Does it overheat even when driving with the A/C turned off? The movement of air over the radiator should be plenty to cool it; the fan should never turn on.
    – Spivonious
    Commented Jul 17, 2017 at 19:36
  • Next time the fan goes inop use a scan tool to command the high and low fan relays. You could also check the ECT and CHT inputs to make sure they aren't going open and reporting -40 or something like that. Do the fans operate normally without the A/C on?
    – Ben
    Commented Jul 17, 2017 at 21:49
  • I'd just wire the fan to a toggle switch in the cockpit. $10 in parts, problem solved. (Of course, I understand if you'd rather fix the problem, but...)
    – 3Dave
    Commented Jul 20, 2017 at 1:32
  • I've been giving the switch in the cockpit idea a lot of thought lately. i have one more trip (and $$) to a performance shop to see if they can find the problem.
    – Zeus
    Commented Jul 20, 2017 at 16:47
  • Does that mustang also have a belt driven fan? Consider the clutch on that as well if so.
    – agentp
    Commented Aug 3, 2017 at 21:15

1 Answer 1



The high speed relay in the CCRM isn't working.

The low speed fan runs at idle or normal operating temps. Once the AC is turned on the high speed takes over. If it is shutting off when the AC is on I'm betting the high speed relay went kaput.

  • While this still may be accurate, the forum thread you posted is for a 98 Mustang GT ... which is about 10 years older than the OP's Mustang. Commented Jul 17, 2017 at 20:13
  • D'oh! Good catch Paulster. Still, it may help in the OP's troubleshooting.
    – Spivonious
    Commented Jul 17, 2017 at 20:23
  • I found the same threads. There are 2 images on that thread, and the first one is for the 2003 GT. It's unlikely there's a big difference in the CCRM from the '03 Mod motor to the '08. I'd say slap a new CCRM in and see if it handles. Unless the OP feels like doing a lot of debugging... then again I have no idea how much a new unit costs... :/ Commented Aug 3, 2017 at 20:22

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