99 Honda Accord V6 heater core question

[PW01]

I'm trying to put a Prestone flush "tee" in a 99 Honda Accord EX V6 sedan. I've installed them in several cars before, but can't seem to find out which hose is the heater core "inlet". On any illustration I've been able to find, they are only labeled as "upper" and "lower". I called the dealer, but could only get a parts guy on the phone and he said he thought it was the lower hose. That just doesn't seem right, and I sure don't want to screw up my Mom's car. She brags to all of her friends how lucky she is to have a son who is so mechanically inclined. I guess I've got her fooled LOL! Thanks for any help!

 

[Sayjac]

Might find what you're looking for with same question you asked on the coolant board, in the thread linked below.

https://bobistheoilguy.com/forums/posts/2082086/

 

[Vikas]

A good way to figure this out is to check the inlet and outlet temperatures. Inlet is going to be hotter as long as you have heat at full blast in the car. You might need infrared thermometer for it though!