Do what the POH says, which may include LOP operations (like the PA31) but if you don't have a JPI or similar, and GAMIs, DON'T attempt to run LOP.
The standard gauges are usually 20+ years old and only read one cylinder or exhaust pipe, which may not be the hottest one. I have demonstrated for a non-believer, running one engine LOP and the other ROP, with the same temps on both sides, but a higher MP and lower fuel flow on the LOP side.
Anyone wanting to know the science, MUST read Deakins discussions based on fully instrumented test-bed engines.
Hi Chuck.