I did an oil change. Thought the car took 4.4 quarts but it only takes 3.7 quarts. I poured in slightly under 4 quarts. The engine is a 1.5 in-line turbo (Honda Civic Si). It’s reading past the fill line slightly. How bad is it? Do I need to pour some out? What am I risking? What symptoms should I be looking for?
Having once upon a time overfilled my oil by almost a quart, I think you are mostly right.
Engine oil should stay in the crankcase. During normal operation, some of it is pumped elsewhere to lubricate the crankshaft, cams, and other mechanical components. The rest of the oil sloshes and splashes around the crankcase keeping everything slippery. If there is too much excess in the crankcase, components moving can push the oil somewhere it shouldn’t be.
In my case, when turning left, the excess oil was pushed passed the piston rings and burned in a huge cloud of blue smoke. It wasn’t a proud moment, but stopping in a random service station and having Bruce try to drain a quart of oil out of the engine, because I couldn’t afford a full oil change was awkward.
… Anyway: all of that to say this:
If you have too little, your oil pressure light will probably come on. If you have too much, you’ll notice it somewhere else.
If you find yourself overfilling often, or if you are in the business and do heavy line work like I did (engine/transmission replacements and overhauls), just save yourself the time and get a vacuum tank with reservoir. If you overfill something you can pump a bit back out, they make them with pneumatic attachments or with a handpump that looks a bit like a bicycle tire air pump. Shove the little feed tube down the dipstick and pump whatever you need to back out.