# High NO at 15mph - everything else is normal on Acura **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [January 30, 2019, 7:09pm UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626 "2019-01-30T19:09:19Z")\ **Posts on this page:** 1\ **Showing post:** 56
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [February 18, 2019, 4:30am UTC](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626/56 "2019-02-18T04:30:35Z")
A mechanic tells me that the increased NOx at 25mph is indication that the combustion is better due to better air flow. In this thread @shanonia stated that the (exceptionally) dark engine oil is due to dirty air filter - factory says every 30k miles - this was in there for 35k - I forgot about it - it was really dirty: [Mobil 1 5W30: Annual Protection Vs Extended Performance Vs Advanced full synthetic](https://community.cartalk.com/t/mobil-1-5w30-annual-protection-vs-extended-performance-vs-advanced-full-synthetic/134378/3) Had it been really warmed up, it would have still passed. For the next SMOG, I would for sure use Redline and really warm up the car. --- _[View the full topic](https://community.cartalk.com/t/high-no-at-15mph-everything-else-is-normal-on-acura/133626)._