Mooney 20C pilot reported operating an aircraft with an open discrepancy in the log book for an inoperative oil temperature gauge.

Narrative

A friend and I who is also a private pilot decided to fly the Mooney to gain more experience in preparation for a mountain flight later that week. We wanted to make sure the plane would perform appropriately to safely fly thru the mountains. We noticed after preparing the plane that the oil temperature gauge was inop as indicated on the dispatch sheet. However; it was marked that this was awaiting review by maintenance. Neither of us remembered or commented that the equipment was required for daytime VFR flight per 91.205. I think we were both naive in thinking that they would not have dispatched the airplane in a situation where it was not airworthy. So; we proceeded to fly the airplane and the oil temperature gauge indeed was not operating. In retrospect; this was not only against the regulations but could have had serious consequences. In the end the flight occurred without incident. Although we did have an oil pressure gauge that most likely would have indicated if there was any issue related to the oil of the engine; we did not have all the information we should have had to make sure the engine was performing appropriately and in a safe operating range. This reinforces that I need to make sure I review everything and not trust anyone else to make decisions regarding the operations of the flight. In the end; I am the one responsible for the safe operation of the flight and I failed this time. As humans; we are all prone to error and no one is perfect. I am disappointed in myself being a perfectionist that I allowed this to happen. I have discussed this with the other pilot and it is a learning experience for us both. I plan to create a checklist of all required equipment for each type of operation (Day VFR; Night VFR and IFR) and will routinely use it before each flight to make sure I have the required items (for legal and safety reasons) moving forward.