I have noticed that my temperature gauge goes to about half way up when the car is warming up after a cold night and then I can see a point where it clicks down almost to the bottom of the range. Presumably this is the thermostat kicking in.

 

When I start the car from cold overnight and I turn on the heater and as the temperature needle is rising before the thermostat kicks in, I am getting warm air. Shouldn't this air be cold until the thermostat kicks in?

 

I am just curious as to how I am getting heat when supposedly the thermostat is blocking the flow of coolant through the system.

The heater core is driven directly off the water pump. Your description of operation is normal. Perhaps the thermostat is slightly delayed. You can consider replacing it along with new coolant and hoses for longevity.

Miles said it well. The surge to half way indicates a sticky T-stat. Fix it, and check the rest of the cooling system at the same time.

a T-stat from Subaru. or your car will overheat

a T-stat from Subaru. or your car will overheat

No need to scare people.

 

I have never bought a t-stat from Subaru and life is generally ok. General wisdom is that the Subaru t-stats are better, with a wider throat opening on them than at least some aftermarkets (I have seen this myself), and some believe that the quality is better.

 

All things being equal, I would probably pay the extra couple of bucks to get the Subaru t-stat, but the world won't end immediately if you get an aftermarket one.

 

And Miles is correct (in concept if not quite literally): The heater bypasses the t-stat and radiator, taking its coolant from the engine outflow and feeding it back in to the waterpump inlet. Subarus have nice heaters.

Edited February 19, 201115 yr by NorthWet

I am just curious as to how I am getting heat when supposedly the thermostat is blocking the flow of coolant through the system.

 

And Miles is correct (in concept if not quite literally): The heater bypasses the t-stat and radiator, taking its coolant from the engine outflow and feeding it back in to the waterpump inlet. Subarus have nice heaters.

 

I disagree with the bypass comment - the heater is a radiator, it gets its coolant from under the thermostat that is then sucked through the heater core back to the water pump to then cycle through the engine block again. This helps for a quick heater, even engine warm up and opening of the thermostat. Thus during cold engine operation the only coolant being cycled is that of the heater circuit - the radiator out front is blocked by the thermostat until the thermostat is warm enough to start opening.

 

The EJ takes it differently - having the thermostat mounted upside down before the water pump on the inlet side of the engine! But the same principal applies really.

 

Cheers

 

Bennie