My jetta uses alot coolent and we have replaced the lower hose the plastic flange and raditer cap

If you can verify there is no external coolant leak, then verify you have no air pockets in the cooling system following the repairs that have been made. If all air is verified as having been purged out, and you still need to add coolant, it could be getting ingested inside the engine due to an internal engine coolant leak. Testing is required.