A320 pilot reported a hydraulic system overheat malfunction after climbing to cruise altitude. The flight diverted to an alternate airport and the hydraulic system returned to normal temperature and the aircraft landed safely.

Narrative

Reaching cruise altitude the ECAM message and procedure HYD G RESERVOIR OVHT (Overhead) displayed on the ECAM. Accomplished ECAM procedure which resulted in G hydraulic system depressurized. The procedure allowed for an attempt to repressurize system G for approach if the reservoir OVHT was no longer occurring. G system pressure and quantity were normal prior to the overheat. All other systems were normal. Had a conference call with Dispatch and Maintenance Control in which it was decided to land short of ZZZ1 at ZZZ. We were above max landing weight and the time enroute to ZZZ would have us land lighter and below max landing weight. If we were unable to recover G system pressure for approach it would require a manual gear extension; no nose wheel steering; one reverser and no normal braking. Under these circumstances I wanted a long runway into the wind with the ability to get towed after landing. ZZZ was a good selection to meet our needs and keep the safety level as high as possible. During approach the reservoir temperature was back to normal and we were able to pressurize the G hydraulic system. The overheat did not reoccur during the approach; landing and taxi to the gate.Cause: Diverted due to loss of use of G hydraulic pressure as a result of ECAM procedure for reservoir overheat.