I have been flying the same C182 glider towplane for the last three years. Recently we noticed some strange EGT behaviour. During runups, the EGTs of the even-numbered cylinders (left side) are indicating about 100º F cooler than the odd-numbered cylinders (right side). See the photos below showing the EGTs for cylinders 1 and 2 during a higher than normal RPM runup (2000 RPM).
The engine is a P Ponk O-470-50, which is basically a carbureted O-520. The anomalous EGT behaviour goes away at full power.
The opinion amongst my club's tow pilots is that there must be uneven mixture distribution to either side of the engine. One suggestion is that there might be an induction leak on the right side, leading to a leaner mixture and hence higher EGTs.
Has anyone seen this kind of behaviour before?