Gas turbine engine heat exchangers and methods of assembling the same

A heat exchanger assembly (130) for use in a gas turbine engine includes a bypass valve (136) and at least one body portion (202). The body portion includes at least one de-congealing inlet channel (248) in flow communication with the bypass valve, a plurality of cooling channels (232) in flow communication with the bypass valve and the at least one de-congealing inlet channel, and at least one de-congealing outlet channel (250) in flow communication with the bypass valve and the at least one de-congealing inlet channel. The bypass valve is configured to deliver a fluid between the at least one de-congealing inlet channel and the plurality of cooling channels during a first mode of operation to facilitate reducing a temperature of the fluid. The bypass valve is further configured to deliver the fluid between the at least one de-congealing inlet channel and the at least one de-congealing outlet channel during a second mode of operation.