2019 Mustang GT Premium Overheating issue

[Jaxstang]

Hello

I bought a new 2019 Mustang GT last week. After 400 miles the temperature started going crazy. The water temp would go from the medium position all the way to the C and completely disappear. The cylinder head temp would go all over the place from 10 to 199 to 160 down to -40 degrees (f), etc. It is the weirdest behavior I have ever seen. Then I get the message that the coolant is over-temperature and I also get the check engine light. I took it to the dealer this Monday (it was on limp mode saying it was overheating but I had just started it in the morning after an overnight cool down). They cleared the code and said it was the thermostat and changed it. I picked it up today from the dealer and on the way home, same thing started happening again so off to the dealer tomorrow to see what the new story is. I think it is either a computer issue or a sensor issue. Any ideas here?

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[Jaxstang]

Here are some pictures that I saved as PDF because somehow I couldn't upload a jpeg

 

[pro 5.0]

Possible air in the system ?

 

[Dusten]

Hello

I bought a new 2019 Mustang GT last week. After 400 miles the temperature started going crazy. The water temp would go from the medium position all the way to the C and completely disappear. The cylinder head temp would go all over the place from 10 to 199 to 160 down to -40 degrees (f), etc. It is the weirdest behavior I have ever seen. Then I get the message that the coolant is over-temperature and I also get the check engine light. I took it to the dealer this Monday (it was on limp mode saying it was overheating but I had just started it in the morning after an overnight cool down). They cleared the code and said it was the thermostat and changed it. I picked it up today from the dealer and on the way home, same thing started happening again so off to the dealer tomorrow to see what the new story is. I think it is either a computer issue or a sensor issue. Any ideas here?

The -40 degrees indicates the sensor is shorted. Either wiring or bad sensor. I'd take it to the dealer and not sweat it.

 

[Jaxstang]

The -40 degrees indicates the sensor is shorted. Either wiring or bad sensor. I'd take it to the dealer and not sweat it.

At the dealer now. Let’s see what’s the verdict. The service guy opened his eyes wide when he saw me. I just left yesterday and back today. Lmao.

 

[local driver]

I'm surprised they didn't suspect an electrical problem FIRST, rather than the thermostat. Doesn't anyone in dealers service departments have any experience at all?

Sheeesh!

 

[Jaxstang]

I'm surprised they didn't suspect an electrical problem FIRST, rather than the thermostat. Doesn't anyone in dealers service departments have any experience at all?

Sheeesh!

I know that’s what bother me that they wouldn’t bother to check sensors or wiring even after showing them the erratic temperature behavior. No word from the dealer today. I’ll call them first thing in the morning. Meanwhile they keep using up my gas driving around testing it. Last time they gave me the car with 2 mikes to empty and I had drop it off with 3/8 of a tank

 

[GT Pony]

I'm surprised they didn't suspect an electrical problem FIRST, rather than the thermostat. Doesn't anyone in dealers service departments have any experience at all?

Sheeesh!

LOL ... yeah, pretty "common" for a bad thermostat to cause the water to freeze (10F and -18F reported by the OP) in the block.

It's definitely a sensor or electrical problem.

 

[Cobra Jet]

LOL ... yeah, pretty "common" for a bad thermostat to cause the water to freeze (10F and -18F reported by the OP) in the block.

It's definitely a sensor or electrical problem.

^^^^^^ LMAO - exactly.... ^^^^^^

So OP, did you ask the Tech if he also replaced the freeze plugs in your block and thawed it out before replacing the T-stat....? LOLOLOL!!!!

Ya know, changing a T-stat on an engine that is at NEGATIVE 40 degrees would be interesting, at least there wouldn’t be any coolant to clean up...

I don’t even want to know what Ford Techs will be like in another 20yrs.... shit, if it’s not blinking or blatantly telling them the issue on their gadget and they don’t do normal “dig in” diagnosis now - imagine 20yrs from now.... holy hell....

 

[Fatguy]

They did the right thing.

A stuck thermostat will wreck the motor so that fix is done first. The sensor problem can wait as long as we know the thermostat is working. I always think the dealership is the devil but in this case the mechanics did the right thing.

 

[Jaxstang]

LOL at some of the comments. So I called the dealer yesterday and they ordered a cylinder head sensor that should be arriving Monday. They haven’t check electrical yet. It feels as if they are doing one step at a time to see what sticks. Hopefully this one sticks. The dealer has my car longer than I have since I bought it. I hope it isn’t a lemon. I would hate to go through the Lemon Law process.

 

[Jaxstang]

^^^^^^ LMAO - exactly.... ^^^^^^

So OP, did you ask the Tech if he also replaced the freeze plugs in your block and thawed it out before replacing the T-stat....? LOLOLOL!!!!

Ya know, changing a T-stat on an engine that is at NEGATIVE 40 degrees would be interesting, at least there wouldn’t be any coolant to clean up...

I don’t even want to know what Ford Techs will be like in another 20yrs.... shit, if it’s not blinking or blatantly telling them the issue on their gadget and they don’t do normal “dig in” diagnosis now - imagine 20yrs from now.... holy hell....

Exactly. I think some of today’s mechanics won’t have a job in 10 years if they don’t up the tech skills. Modern cars are too complex with computers and electronics.

 

[GT Pony]

LOL at some of the comments. So I called the dealer yesterday and they ordered a cylinder head sensor that should be arriving Monday. They haven’t check electrical yet. It feels as if they are doing one step at a time to see what sticks. Hopefully this one sticks. The dealer has my car longer than I have since I bought it. I hope it isn’t a lemon. I would hate to go through the Lemon Law process.

Didn't the dealership do a diagnostic scan on your car to see what the trouble-codes told them?

 

[Jaxstang]

They did and didn’t find a code well they called me yesterday that the car was ready. It was too late to pick it up and today I was on a trip so I’ll get it in the morning. Hopefully no scratches or issues. I’ll update tomorrow

 

[steveo1960]

This is like troubleshooting 101....

Step 1: Is the car really overheating? Steam? Smoke? etc....
Step 2: Yes... Physical problem: a) Thermostat, b) low coolant/wrong coolant c) collapsed hose d) blockage e) water pump f) belt etc
Step 3: No it's not really overheating. No signs of over temperature.
Step 4: Monitoring problem. a) Sensor b) computer) c) fuse etc.....

This should take about 2 minutes hooking up a scan tool.

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