So I drove the 1995 to work yesterday. It sat covered in the parking lot for 9 hours. After work I started it up and noticed the coolant temperature showed 107 degrees while the outside air temperature showed 92 degrees. I understand there is probably some radiant heat from the asphalt, but 15 degrees difference? Is this worth investigating? Everything works great on this car, I just don't understand why the readings are so different after sitting for 9 hours under a cover.

 

Its fine, let it sit for a day and see what it reads.

 

Two different sensors, neither of which is calibrated.

Steve

 

9 hours, You have over 500 lbs of mass plus fluids under a hood. It'll take over 24 hours to get to ambient. Leave the hood up and it'll be a few hours quicker.

 

Cooling isn't linear so... If you were at 180 still I'd investigate.

 

The CTS units are known to fail and frequently are not discovered until the car won't start when cold or the car runs really rich (killing the gas mileage) thinking it is very cold outdoors all the time. The CTS is an essential sensor in the Fuel System Injection system.

I would let the car sit for 24-48 hours and the numbers should be very close or I would replace the CTS. One thing to try before replacing parts is to clean the connectors of the CTS, that alone might make the numbers get closer together. Dirty connections plague C4 Corvettes. If the CTS is still wrong then I would suggest you replace it. Mine has three wires going to it, Reference voltage, signal return and ground. The chart in the FSM is very handy verifying your CTS.

The other thing to check is your engine's Ground. Using a multi meter you can measure the battery voltage at the battery, then measure the voltage using the engine in place of the battery Ground, black lead to engine block and red lead to battery positive. The numbers again should be the same or very close. If the engine has a bad ground that would make big issues for the C4. The engine sends 12 volts to the injectors whenever the key is on "start" or "run" and the computer supplies the ground when it wants fuel injected. Good battery connections are critical for proper operation of the electronic fuel injection.

Check your fuse panel for the proper battery voltage when you can. I have a 1988 C4 that had major corrosion causing a almost 2 volt drop in voltage inside the Corvette. There are several ground straps that have to be working properly for the accessories to function. I found a broken ground strap near my exhaust and after reconnecting it my antenna started working again!

Like mentioned by 383vette, there is "a lot" of heated thermal mass that takes a long time to cool off. This is worse when your ambient temperatures are high. If it were 40* outdoors the car might have cooled down faster, even under a cover...

Good Luck with your Beautiful Corvette!

Best regards,
Chris

 

A lot of thermal inertia to cool down, don't worry about it.

I see it every day in summer.

 

Same happens to mine, nothing to worry about. If you were to hook up a data logger or app-based OBD2 scanner to a more modern/newer car, you'd see the same.

 

No problems; then no worries. Unless you have nothing else to do.