Ok, so my tC with 91k miles on it has developed an overheating problem. But it's not your typical overheating. Here's how it overheats:

1. While at idle (or in gear but not moving) with the A/C OFF, the car will start to overheat. The needle has gotten past the redline, but most of the time, I stop it by turning the A/C ON.
2. While at speed (>20mph) with the A/C OFF, the car will return to normal temperature.
3. While at idle with the A/C ON, the car will not overheat.

So basically, I have to leave the A/C ON in order to keep the car from overheating if I'm in stop and go traffic. If I'm on the highway, I can turn the A/C OFF and be fine.

I can hear the A/C fan kick on when the A/C is ON but with it OFF I don't hear the normal engine fan. However, I have opened the hood and noticed the normal engine fan is turning.

Any ideas? I have some, but I'm going to see what you guys say first.

 

If you leave it sit at idle, do the cooling fans turn on w/o the A/C on? The fans kick in at 202F degrees. Running for just a few seconds it should cool you down to around 190F degrees.

What is your cooling mixture?
OEM thermostat?

 

At idle with the A/C OFF, only one of the cooling fans kicks on. At idle with the A/C ON, both kick on.

Cooling mixture is whatever the stock one is: Haven't touched it.

OEM thermostat.

 

have you done anything with the cooling system at all or this just started happening.. sounds like your cooling fan is going on and off and when u turn the a/c fan on it cools it down.. but doesint the a/c fan come on with the other one? i havent had stock fans in so long

 

If its not a problem with your fans, try a new thermostat. Its cheap and easy to install.

 

coolant temp switch, when you turn your A/C on your fans cut on, without the A/C on the car is waiting for the temp switch to cut them on, part is like 35 bucks and there easy to put in.

 

Ok, this is what I was leaning towards, but wanted to hear what others said.

I don't think it's the thermostat because otherwise coolant wouldn't be getting to the engine at all, correct?

Anyways, I'm gonna replace this part, then I'll update and let you guys know what happens.

 

Id also do a coolant exchange if you have been over heating

 

so glad i live in florida i use straight up water and water wetter

 

yeah you're lucky. I go to college in Cleveland, OH...

 

Sounds like the cooling fan died to me. The ac fan turns on when you turn your ac on so that would help with cooling

 

I would imagine you would get a CEL if you had an out of range CTS. It sounds like you got an intermittent cooling fan control issue. I would suggest looking at the cooling fan relays. Try swapping the relays from another circuit and see what happens.

 

Ok, a little more info on this:

Did some testing today, I'm pretty sure it's the ECT.

Here's what I did:

1. With the car running, temp gauge normal, and A/C OFF, both fans do not turn.
2. While in this configuration, the temp started to climb. I let it climb almost to the red. both fans still did not turn.
3. I turned on the A/C and noticed both fans run. Temperature returned to normal.

This tells me a couple of things:

1. Both fans are operating correctly. Meaning, they work, and are not defective or broke.
2. Turning on the A/C activates both fans regardless of engine temperature.

I would think if the relays or the fan itself was bad, I wouldn't see any movement at all. Also, I'm not sure that a defective ECT would necessarily throw a CEL. But I could be totally wrong.

I ordered a new ECT from O'Reilly's auto parts. If anyone is interested you can find it here:

http://www.oreillyauto.com/site/c/se...keyword=wt5123

Anyways, gonna throw this thing on tomorrow and see what happens.

 

Yea, the ECU uses the ECT value for a number of things like when the engine goes into close loop at a certain temp, and ofcoarse cooling fan control. You would definitely get an CEL with a bad ECT since it's emissions related.

Btw, I just checked out under my engine bay and there are more than one relay controlling power supply to the cooling fans. The relay cover says there are 3 relays. Hmmmm... but only 2 fans.

 

Ok you said the coolant is original and you've never touched it, and the thermostat is original. You never said if you checked the fluid level was good. if it is good the first thing i would do is check the coolant with a coolant refractometer to find out the condition of the fluid. also i would get a temp gun and check the temp of the coolant at the thermostat and at the top radiator hose will its over heating to see if the vehicle is actually over heating or if its a coolant temp sensor issue..

 

Looking over the wiring diagram I believe it has to do with the pressure switch (whatever that is...)

Anyways, I'll test the relay theory too. I can always take the ECT back. Thanks for the info!

 

That was the first thing I checked (coolant level). It has plenty in it, and if it were a coolant problem, it would alway overheat (even with the A/C on).

 

So I'm having the same issue you had im just wondering...was it that you needed to replace the ECT ? Or was it another problem ??

 

i just went through this same issue added coolant and replaced the temp sensor seems to have fixed the issue so far