I can only speak regarding my
06 Limited HL with Rear Heat Register at the Third Row Seating.
It does
not blow as hot as the front underdash footwell. Never did and never will. The
non-insulated aluminum heater lines (feed and return)run underneath the chassis outside of the cabin
and by the time the hot engine coolant makes it to the heater core at the rear seat it has cooled down considerably. My Infrared thermometer verifies this. Depending on the ambient conditions, may even be 20 Degrees cooler.
It does displace colder cabin air in rear.
It does balance out the heating in the whole cabin better/faster than without the rear heater on.
I have considered insulating these lines but having considered where these lines run near exhaust pipes etc. it may be impractical at least for 50% of these lines.
PS my heat blows the same temp whether I'm moving or not.
But it would make sense that if the vehicle is driving, that the engine's water pump is much more active and would pump heat faster to the rear Heater core.
Good luck.
Maybe someone with an 08 can chime in at some point.
LT
2008 highlander heater question
Linear Mode
