160,000 miles mostly 4k OCI w/ 5w30 dino (typically Chevron Supreme, Mobil 5000 or Formula Shell) and FRAM orange can filters.... but last couple years i started to use more synthetic oils with better filters and longer OCI... car runs great on everything... 90% highway miles last few years..
Had a bunch of Castrol GTX semi-syn high mileage 5w20 (green jug) from a previous vehicle i needed to use up.
So last OCI was 6500 miles and 3 months using my own brew of half GTX 5w20 and half whatever 5w30 dino oil i had on my shelf. Oil looked clean enough but i noticed varish around the fill hole i've never seen before. Is varnish a major red flag?
What's the likely culprit? Introducing 5w20, Castrol GTX? both? neither?
(I dumped it and replaced with M1 HM full synthetic with M1 filter)
Had a bunch of Castrol GTX semi-syn high mileage 5w20 (green jug) from a previous vehicle i needed to use up.
So last OCI was 6500 miles and 3 months using my own brew of half GTX 5w20 and half whatever 5w30 dino oil i had on my shelf. Oil looked clean enough but i noticed varish around the fill hole i've never seen before. Is varnish a major red flag?
What's the likely culprit? Introducing 5w20, Castrol GTX? both? neither?
(I dumped it and replaced with M1 HM full synthetic with M1 filter)