i need to change my antifreeze in my 2006 impreza someday or just add more,do i have to use subaru antifreeze and conditioner or is there a suitable substitute?

Any of the green stuff (universal) works fine. Best results are to drain and fill. (I run a garden hose to mine in between in case there's any stuff that needs flushed out.

 

Subaru coolant conditioner can be added seperately. It's about $3. a bottle from the dealership. It's not essential, but is supposed to extend the life of head gaskets.

I buy and use the 50/50 mix of green antifreeze, so don't have to add distilled water. I, too, recommend using the Subaru coolant conditioner to help stop any coolant leak at the head gasket.

I too do a water flush after draining the old anti-freeze.

But this always leaves some residual water in the cooling system - sometimes quite a lot.

So adding 50%/50% premix doesn't work after a water flush.

 

What I do is to calculate how much of the concentrated anti-freeze that I need (knowing the capacity of the cooling system).

Then I add that amount of antifreeze to the system.

Then I top up with water. Run the car for a day. And then top up with water again, if necessary.

 

That way I end up with the correct antifreeze+water mix.

I would strongly urge you NOT to flush with a garden hose or anything else.  If you don't have a clogged up system, you don't need to flush.  Call the dealer and ask how much the Subaru Coolant is.  Then compare it to the universal long life coolants from the major brands and decide if the cost/comfort level is there.  If the Subaru coolant was only a dollar more, would it be worth it to you to use it.

 

But I believe that any of the major brand universal long life coolants will work just fine, but if you are the least but uncomfortable with that, then the factory fill may be the best way to go.  A good nights sleep has value too.  I'm told that of all the major brands, Peak is the closest to the Japanese specs and closest to Subaru's specs.

Is the Walmart brand the best deal, or could you do better pricewise with Advance auto and Auto zone product with their online discounts?