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Q: Noise in heater core over 2300 rpm. on 2000 Ford F-150

Replaced heater code and coolant flush. Now have a noise under dash at RPMs over 2300. Sounds like squirting water through a hose. Have driven this way for a month now. No noise under 2300. Also can not hear it in engine compartment, only in cab with doors closed. Possible to have air trapped in core..? How can I bleed the air..? Thanks!
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That may be the reason you hear the coolant flowing through the heater core! If heater output is ok with no engine overheating, drive it!
Different flow rate and baffling (or lack of) in the new core.
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Its very likely that's what is going on, there is an air pocket in the heater core. With the engine off and cool, one way is to take one of the heater hoses off and use a pressure tester to push coolant through the core while blocking the open hose with pliers or a finger, and then switch it and block the core with your finger while bleeding the hose. With a fairly new tool that most shops have today, "The Air Lift" we fill cooling systems by first pulling the system into a vacuum and then letting the vacuum draw the coolant into the whole system. Without these tools another way would be to remove one heater hose and attach a piece of extra hose to the heater core, now pour coolant into that hose which will fill the core and push air out of the open hose.
Thanks! For your second suggestion (last sentence) could I simply pull the hose off the thermostat housing, hold it above the core height, and slowing pour coolant into it to replace the air, then pinch (hopefully not create another air pocket!) and reinstall to housing...?
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