On a hot day, when my vehicle has been idling for a while, the engine sounds like it is running very fast. The tachometer indicates normal, could my transmission be slipping?
If the tachometer shows normal RPM for the speed driven, the transmission is likely not slipping. If the noise only occurs on hot days and after sitting at an idle, I would suspect the cooling fan(s). Electric cooling fans are commanded to high as temperature increases. Mechanical fans normally have a clutch that increases fan speed as temperature rises. Running at high speed the fans create a noise, much like the engine running faster. This is normal operation, as long as the noise goes away after driving at speed and when the engine cools down.
