2010 with 206k miles. I've had engine knocking in all weather, not just cold, the last 1.5 years or so. It's not every time, and it's only on start up. It's also relative to oil loss on the dipstick, ie harder knocking the lower it is on the dipstick. Of late, the dipstick has be harder to read. It was high/smeared on both sides of the dipstick. Got the oil changed, now it only does it on 1 side. Photos attached. *No apparent coolant loss. Both containers have not moved. *About 80K miles since last spark plugs change Today, I accelerated quickly at one point and drove it aggressively for maybe 15-20 seconds. I then parked the car for 2 hours. When I went to start the car again, I noticed the engine check light. Put in the sensor, opened Dr. Prius. P0301 code. I cleared the code. Turned off the car. Restarted, drove 10 miles, got unusually good gas mileage. Then parked it at home. I've since restarted it a few times and no code. What's my order of operations here? Swap coils and see if it misfires again? Then change spark plugs? Or is the oil dipstick pointing to head gasket?
I feel like my dipstick is always high on once side like you describe I would swap coils and spark plugs and then start saving for a head gasket or lower mileage engine. I would expect knocking from a head gasket to be the morning after a long drive when the engine and coolant has a chance to fully heat up and pressurize.
Often mis From my experience on that code after you address the coil issue normally will tell you a bad cat converter code efficiency loss. As in platinum dust honeycomb clogged maybe cause of bad running oxygen/fuel levels overtime. Cake up. Also regular piston wall ware etc at that mileage. Causing piston slap or even maybe you have rod knock or a rod pin ware. Lots of moving parts .. all ware and tare in time old saying if it moves it breaks.
Just for due diligence, swap (say) cyl one and three coils/plugs, see if code changes to P0303. Still, with your miles, symptoms and code, it’s very likely to be head gasket failure. looking through previous threads you’ve started, the cars been “ailing” for some time.
