Temperature measuring on RC engines is very difficult due to the fact that you can't get the really interesting measurement: online EGT at various engine loads. What's interesting to know is the EGT since this is a direct measure on the AVERAGE oil outlet temp. If this temp gets higher than the max design temp for the oil, a large part of the oil will start to decompose or polymerize. This will give varnish / carbon deposits / total oil film breakdown, which can lead to engine failure......
In daily life it is best to use a calibrated IR-gun on the engine plug at the highest load you operate in!