Engine 2005 GT Running Hot After 30 Mins of Driving. Please help!

lawd..hammercy · Aug 16, 2018

I have an 05 GT that runs hot after driving for about 30 mins or so. What happens is the gauge goes up about a quarter way past half way, but does not go all the way to "H". It eventually regulates itself and goes back to halfway (operating temp), and it will do this randomly after the car has been driven for 30 mins (so more than once per drive past 30 mins). This would apply to "city" driving only as I have not run it on the highway since this has started. I changed out the thermostat, and it does the same thing. I am hoping that the thermostat was defective out of the box because my mechanic looked at the car and said he cannot see anything else wrong with the cooling system. The thermostat used was a fail safe from Autozone, but I am picking up the OEM Motorocraft from Ford today. Per the mechanic, fans, hoses, air filter, radiator, coolant, etc all look good. No smoke coming from the exhaust and the oil is not mixing with the coolant so I ruled out the head gasket. No check engine light either...

This is driving me nuts, and hopefully one of you can help me with this!

lawd..hammercy · Aug 16, 2018

A quick update on this:

For the second time, when driving for about 40 mins, it did what it does above, but the car started making a crazy sound. Almost like a misfire sound but coming from one of the cats if I had to guess. The sound is crazy enough to make me turn the car off immediately. When I restart it seconds after I turn it off, the noise is gone. Is it possible one of the cats is clogged and causing this without setting off the check engine?

Dino Dino Bambino · Aug 17, 2018

It's possible.

lawd..hammercy · Aug 17, 2018

Bullitt95 said:
It's possible.

I have it at my mechanic now to put the motorcraft t-stat in. The noise that I heard I am almost positive was the car going into limp mode. What baffles me is the wrench light nor check engine light went on. Maybe because I basically turned it off immediately? A coworker had a Volkswagen GTI that did something similar and it was the water pump on the way out. I asked my mechanic if he could check the cats and the water pump while he has it. I'll keep this thread updated.

lawd..hammercy · Aug 20, 2018

New t-stat was put in. That is not the problem. Mechanic said water pump and cats tested fine.

He ruled out any trans or head gasket problems (not losing coolant so no head gasket issue). He claims I would know if the trans was dragging on the engine. He has driven the car multiple times and said he doesn't see any issues with the trans.

His conclusion now is that the car is not actually running hot. He thinks that the engine temp control sensor is going bad. I wonder why it isn't throwing any codes, but he said it might not be failing "enough" to throw a code yet.

Anyway, I'm hoping someone has experience with this issue and has some feedback for me. I will keep this post updated as much as I can in the event that someone has the same issue and can find some of this information helpful.

lawd..hammercy · Aug 20, 2018

A quick question for those that can hopefully answer...

If it is the cylinder head temp sensor, why would it not set off the temp icon light on the dash? No CEL, no temp light, nothing! I am almost positive it went into failsafe or limp mode twice because of this issue.

Dino Dino Bambino · Aug 24, 2018

lawd..hammercy said:
What happens is the gauge goes up about a quarter way past half way, but does not go all the way to "H". It eventually regulates itself and goes back to halfway (operating temp), and it will do this randomly after the car has been driven for 30 mins (so more than once per drive past 30 mins). This would apply to "city" driving only as I have not run it on the highway since this has started.

My advice is to run the car on the highway for 30+ minutes and if the temp. gauge doesn't go above halfway, it would be safe to assume that the problem is indeed confined to city driving. In that case, I'd say that one of the fan relays (probably the low speed) is intermittently failing, and the high speed fan relay kicks in when the temp. gauge gets to 3/4 to bring it back.

lawd..hammercy · Aug 24, 2018

Thanks for your feedback. I replaced the cylinder head temp sensor last night. Today it spiked a little bit after running it for 45 mins. It spiked after I ran it hard, so maybe that's why. It never did that before this problem though. I would say the new sensor was an improvement, but still somewhat of an issue exists based on that. Have you ever had your temp gauge spike a little past halfway normally? It is a little cooler today, but if it is an electrical issue and was giving false readings, I'm not sure how the outside temp would affect it. I feel like when it was cooler out and with the old sensor the gauge was acting worse...

lawd..hammercy · Aug 26, 2018

Bullitt95 said:
My advice is to run the car on the highway for 30+ minutes and if the temp. gauge doesn't go above halfway, it would be safe to assume that the problem is indeed confined to city driving. In that case, I'd say that one of the fan relays (probably the low speed) is intermittently failing, and the high speed fan relay kicks in when the temp. gauge gets to 3/4 to bring it back.

My buddy (mechanic), and I spent all day messing with the car. We narrowed it down to the fan not turning on early enough. The scanner shows the temp reaching 230 degrees before the fan kicks on. I believe the ecm is programmed to turn the fan on no hotter than 228 degrees (could be wrong). I have the factory tune on it, so we are not sure what is causing this. We tested the relays and they are fine. We used a relay switch and can turn the fan on by command. Somehow there is a disconnect or delay in signal between the ecm and the fan. It's hard for us to tell if a new fan is necessary or if the problem is not in the actual fan. I have a Duralast cylinder head temp sensor that I put in just 3 days ago, so I was hoping someone here knew what could be causing this....

Dino Dino Bambino · Aug 27, 2018

The high speed fan mode should kick in at 228*F so it seems that it's working as it should. However the low speed fan mode should kick in at 216*F and that isn't happening. If the low speed fan relay is OK, the BEC to which it attaches may be burnt out.

lawd..hammercy · Aug 27, 2018

The BEC is the fuse box, correct? How do I check it? It's not the top part of it, because that looked fine.

If the BEC is fine, should I just get a new fan? I was reading that some other S197 owners had an electrical issue to where that had to bypass and hardwire straight to the fan.

lawd..hammercy · Aug 27, 2018

Here is the problem (I hope). Ford claims they are discontinued and cannot get them. Any idea where I can get the fuse block?

lawd..hammercy · Sep 3, 2018

So the blown fuse terminal was certainly the issue. I cleaned it up and tried to raise the terminal tab as most as possible. So far, so good. I feel like it could disconnect at any moment again. Any advice on a permanent repair for this? I tried to buy the block itself, but I need to buy the whole fuse box. The ones offered on eBay are unclear as to whether or not the blocks are included with the fuse box. The fuse block itself is almost impossible to find.

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