Toyota Highlander - One hour loss of heat

Recently the thermostat was replaced in my 2005 Toyota Highlander. After driving for about one hour, rather than heat the fan blows out cool air. The mechanic can’t find a problem, but the vehicle has only been driven for minutes when they check it. I believe if it ran for about 1 hour it would blow cool air. I live in ND and yes at night I still need heat.

Has your mechanic checked to make sure there is no air in the cooling system? Do you know what the mechanic has checked?

I was told they hooked up a device to determine if the heat was at a normal range. It was. That is all I was told and didn’t know enough to ask further questions.

Is your coolant filled to the correct level?

I agree that there could be air trapped in the system if not bled properly.

The last time it was checked the coolant was at the correct level.

Is it a simple process and should I make an appointment to check for trapped air or should I try again with – my heater cools after about one hour?

Keep checking the coolant level. If there’s trapped air, it may work itself out. Drive it for an hour and see what happens to the temp of the heater core. If same problem happens, see if you can feel the 2 coolant hoses running from engine into/out of the heater core and report back. (both cool, or both hot, or 1 of each.)

How does temp gauge in dash behave? Watch this closely.