Everyone's so concerned about the operating temperature of the Airtag or battery (140F) yet has no concern about the gasoline reservoir also inside the case...
Serious - the exhaust system is designed to push the heat out of the casing. If truly concerned about how warm the Airtag gets, locate it near the air filter / intake so it'll stay close to ambient temperatures.
Common misconception - the map location is NOT the location of the Airtag, it's the l
ocation of the device which last picked up the Airtag's signal. So the map location for your car's airtag would've been the location of the person's phone who parked or walked or drove by close enough for their phone to hear the Airtag's broadcast.
Similarly,
@monstermash might go to the map location, but that's just saying the location of the phone which last heard from the Airtag. If that timestamp is recent then the AirTag is likely nearby and walking around with Precious Finding on should locate it. If the timestamp is older though then it's likely the AirTag has been disabled and moved.
Either way, finding lost stuff isn't what Airtag's are marketed to do - so don't expect them to be stellar at doing that job. With a car, you'd do better with a real GPS tracker that sends it's own GPS location. They - and associated service plans - are pretty cheap.