I purchased this vehicle from a (Toyota) dealer
a couple of weeks ago. There is an odd heating
problem.

Sometimes it behaves, and I have full control of
good hot heat inside the cabin.

Other times (especially when the ambient temperature
goes down to the 30s or below) I can't get any heat
at all from the vents, or hardly any at all. The
temperature gage was warming up to just below half.

But sometimes, it goes higher. I was afraid it was
really overheating, so once I had it towed back to
the dealer. They said it was a bubble in the cooling
cycle, and gave me the car back after backflushing
it. They assured me that it had coolant.

So it behaved in the middle (warmer part) of two
days again. But in the evenings (colder) it won't
give me heat.

And tonight the temperature gage went high again.
I don't believe it is actually overheating based
on the diagnosis so far. So I continued to drive
it this time. It went up, down to 3/4, once to
half, back up, up to red, up to pegged, and I
kept driving. With no heat in any vents no matter
what I did with the controls. And it did not boil
over.

Is there a T sensor on/in the engine that may be
defective and bads signals pegging the gage and
causing the inside heat not to get any hot water?
(I have no idea how much "smarts" they have in the
heating system of this car).

Any other ideas? I've reported it to the dealer again
and will be going back, but they had it two days and
it came back in the same condition, so I'm hoping
for a real diagnosis here.

Thanks, John