So far I have 6,200 miles and 6 months on this fill of Pennzoil Platinum, with a PureOne filter, in the Civic. I have a 400 miles round trip coming up. Part of me wants to change it and part of me wants to push it to 7,000 miles. What do you think? should I change it? There's been no make it oil (yet) since it's about 1/4 qt. low I might add just add to top it off.