Can I switch from conventional to synthetic oil at 100k miles?

It's an old wives' tale that had some truth in the 1970s-80s but is completely outdated now. **The original concern:** Early synthetic oils used a different base (polyalphaolefin + ester blends) that could shrink certain old-style rubber seals, causing leaks. Those seal materials haven't been used since the late 1980s. **Modern reality:** - All major synthetic oils are fully compatible with modern seal materials - API certification (the donut on the bottle) requires seal compatibility testing - Toyota itself recommends synthetic for your engine **The "cleaning out sludge" concern:** Synthetic does have better detergent properties. If the engine has significant sludge buildup, switching to synthetic CAN reveal existing leaks that were plugged by sludge. But here's the thing — those leaks already exist. The sludge was masking a problem, not solving it. At 102k on a Camry with regular oil changes, you probably don't have significant sludge. Switch to synthetic and enjoy longer intervals and better protection. Your 2AZ-FE will love it. **If you're nervous:** Use a high-mileage synthetic (Mobil 1 High Mileage, Pennzoil Platinum High Mileage, etc.). These have seal conditioners that keep older seals supple. Best of both worlds.

Switched my '07 Camry to Mobil 1 at 95k. Zero issues, now at 215k and the engine is clean as a whistle inside. Do it. The "causes leaks" thing is pure myth at this point.