05/30/2026
Myth Buster Friday Answer
FALSE — though this myth has a historical origin that made it partially true for a brief window of time and has been carried forward inaccurately ever since.
In the early days of synthetic motor oil — primarily in the 1970s and early 1980s — some synthetic formulations used an ester base that caused certain older rubber seal compounds to swell or deteriorate at a different rate than conventional oil. Engines from that era, particularly those with seals made from materials that were not compatible with the ester chemistry, did occasionally develop leaks after switching to synthetic. Modern synthetic motor oils do not use those seal-aggressive compounds. They are formulated to be compatible with the seal materials used in every engine produced in the past several decades. Switching from conventional to full synthetic in a modern engine, or even in most engines from the 1990s onward, does not cause seal leakage. What synthetic oil can do is clean deposits and sludge from an engine that has been run on degraded conventional oil for a long time — and those deposits were sometimes what was keeping a worn seal from leaking. In that case, the synthetic did not cause the leak. It revealed a seal that was already compromised. Hope everyone is enjoying Riverfest weekend — see you Monday at 7:30.
