I got a P0301 misfire on 05 Civic with 60,000 miles. I have swapped the coils and changed the spark plugs but I still get the same code. A compression test was done and no issue was found. I have noticed that I need to top off the coolant every few weeks but I don't see any leaks. What could be the problem?

 

Take the plugs out. If one of them looks a lot cleaner than the others, coolant is leaking into that cylinder through the head gasket. A small leak will not show on a compression test.