Switched to a 5w40 synthetic after 200k miles, wish I had done it sooner

My old 7.3 Powerstroke always had a little knock on cold starts, especially during those January mornings here in Montana. I ran the same 15w40 conventional oil for years because that is what the previous owner used and I figured why mess with what works. Last month I finally did an oil analysis and the wear metals were high, so I swapped to a full synthetic 5w40 and changed the filter. The cold start knock is basically gone and my oil pressure comes up way faster, which makes sense now that I think about the flow characteristics. I also noticed the engine idles smoother and I am not burning through as much oil between changes. Has anyone else made this switch on a high mileage engine and seen a difference in startup noise? I am curious if this is just placebo or if the thinner cold viscosity really is doing the work.

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baker.ben28d ago

That "cold start knock" being gone is no placebo, trust me. I did the same thing on my old Chevy with 240k on it and the difference was night and day. The 5w40 gets moving faster when everything is stiff and cold, so the bearings and lifters are actually getting oil instead of just sitting there dry for those first few seconds. The smoother idle and less oil burn are probably because the synthetic keeps the seals and rings in better shape. Your oil analysis showing high wear metals was the real kick in the pants, that data does not lie. Keep using it, your engine is thanking you every time you turn the key.