I've seen this problem on O-235s fitted to C 152s. At the time we had several piston plugs "fail". Apparently there was never a problem with the O-235s fitted to the PA38. This led us down the path of wondering why a problem with the C152 but not the PA38, essentially same engine in both.
The PA38 never had an oil cooler fitted whereas the C152 did. Blanking of the oil cooler on the C152 cured the problem if I recall correctly.
Last edited by 27/09; 4th April 2013 at 08:47.