This is not a how to question, this is a flow direction question.

I'm assuming the "hot" coolant would go in through the top connector of the heater core, and the return "cool" coolant would come back through the bottom connector of the heater core.

I'm planning on flushing the heater core this weekend as my heat is warm, but not blazing like it used to be. I just want to make sure I back flush it the first go.

Thank you!

FSM shows in the bottom and out the top.

Ok then, glad I checked.

Thanks!

x2

Some heating issues can be a junk thermostat as well. as long as you are flushing that will probably help as well. You probably knew that but just in case I thought I would mention it.

My thermometer is dead steady on 210, so I don't think that would be the problem, and I thought the heater core was part of the engine circuit, not effected by the thermostat...

I am pretty sure flow direction doesnt matter for the heater core. All it does is use the hot water to make hot air.

Theoretically it should have flow, otherwise it would never get warm. The same fluid would just sit there all the time.

For the same reason coolant is pumped from the bottom of the engine up, heat rises. Allowing coolant flow from the bottom up allows it to heat the core most efficiently.

Plus the inlet and outlets are two different sizes of hose so its impossible to mix them up.