air in the cooling system will create a sloshing sound in the heater core, which is sliightly to the passenger side of center. if you've recently had the system open, air was left in and will usually work itself out as long as the overflow tank is full. if you haven't recently opened it, you may have a leak that's letting in air.
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01 1500 Reg Cab 4wd 5.2 auto 3.55 285/75/16 nasta step bar tow hook sc3815 180 3923 trans cooler/filter posi-lok powertrax noslip timbren brite-box pioneer head rockford amp/speaker cobra cb firestick hughes plenum water pump timing chain oil pump rear seal front bearings brakes shocks cracked dash towing composting boat.
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