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My buddy swore I needed synthetic oil in my old Corolla. I called him crazy for 6 months.
He kept telling me the 5W-30 conventional was fine and that synthetic was a waste at 180k miles. I finally tried it after an oil change special at the shop near my house in Austin and my cold start knock went away in like 2 days. The engine idles smoother now and I swear I picked up 2 MPG on my highway commute. Has anyone else seen that big a difference switching on a high mileage car or was my engine just being dramatic?
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beth_park3mo ago
180k on conventional oil and then switching to synthetic is asking for trouble, not a cure. Those seal conditioners are snake oil at that mileage. You've been running sludge through that motor for 15 years, now you switch to a detergent that strips all that built-up gunk loose and it clogs your oil passages. I've seen guys do this and blow their rear main seal inside a month. Your cold start knock going away is probably a coincidence or the placebo effect from paying for a fancy oil change. Keep the conventional in it and save your money for a rebuild.
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matthew3713mo ago
Good move trying it. High mileage synthetics have special seal conditioners. That's probably why your knock went away. The old conventional oil couldn't keep the seals pliable at cold start. On a 180k motor, any extra protection helps.
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wright.leo3mo ago
Man, that's wild but I've heard similar stuff from a few people. @matthew371 is spot on about those seal conditioners - I remember reading somewhere that synthetics can really help with cold starts on older cars. Glad your Corolla is running smoother now, sounds like it was worth the switch.
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