Cooling system

Heater inlet hose, Which one is it?

The larger hose or the smaller one? (or)

The one that comes out of the top of the water pump or the other one?

1997 GMC truck/ 350 motor Thanks!

Do it the messy way, take the hose off have some one turn the engine over and see which way the coolant flows if it comes out of the hose you have the inlet hose, if it comes out of the heater core it is the other hose is the inlet. If you are trying to flush the heater core remove both hoses, and run water in both directions until the water is clean, you don’t want the dirt or sediment clogging the radiator or the heater core again. Not sure of your objective.

Installing flush & fill kit.

The hose from the water pump to the heater core is the inlet hose.


And it’ll be a little over an inch in outside diameter, not a larger hose.
The larger hoses carry the water in and out of the radiator from the engine.

The heater core is located on the firewall, basically the metal between your feet and the engine, though probably the passengers feet. Follow the hose from the firewall to the pump and I think you will have it. Just in case when flushing you need to get the engine warm enough so the thermostat opens for thorough flushing and do not add cold water to a warm engine if it is not running.