It has been over 100 degrees here (over and above 110) for over 3 weeks. Recently my 2001 S-Type 4.0 V8 has failed to start when left in the heat. I will drive for awhile without issue, but as soon as I turn the car off - nothing on restart. All the lights and bells and whistles work (radio, etc.). I have a one year old battery that I just had checked - charge is great. If I wait about an hour (up to as long as 3), the temperature gauge will go from normal to 1/4 (cold), then the car will start. Has anyone ever seen this before?

 

Sounds like a weak starter solenoid or very high resistance in the wiring. Check all the grounds and connections as a first step.

 

+1 on Mikey's response - heat soak (starter solenoid) or starter is on it's way out. Be prepared - the starter is underneath the intake manifold and is only accessible from the top of the vehicle. (I stand corrected - I was under my S Type last night and the starter seems accessible from beneath the vehicle)