'08 Heater - Warm But Not Hot

I had a -20°C (-4°F) commute the other day too. My coolant temp actually got to 70°C (just under 160°F), with 80% grille blocking. That made for a comfortable 25 MPH drive on the icy highway.

When the temperature climbs to just under freezing, you can melt stuff with the heater... which is why I choose not to block completely. The heat is always set at MAX HOT with the blower somewhere at a middle speed and no recirc.
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Yes, block the grille and heater performance is much better. Do *not* block the radiator itself, that is very dangerous

I also block the grille on my FJ as it really makes a difference in heater performance, especially -30 C and colder

 

I am having same problem with mine

 

Is your mpg down in the 30's also? If yes, it is a bad engine thermostat.

Without the thermostat working properly, the engine never builds enough heat to make the car warm inside.
Not a complex fix. Any mechanic can fix it. It's not even a Prius specific part. The same thermostat is used in the Camry and more.

 

Someone else's video on the topic of replacement.