This one have me a laugh. This is for a VW MK7 GTI that is a track car (not a daily anymore). She states she went up a grade to a 10W-40 from what I presume was a 5W40 Euro VW502 oil. She also states this dropped her oil temps 20 deg.
Firstly...aren't most 10W40s lower quality oils vs. a Euro 5W40? Many aren't even "full synthetic" correct? I usually think of 10W40 as an old-school oil for old-school vehicles...not something I'd use for track use vs. so many other better choices.
I don't typically believe anyone that states wild drops in oil temp without before/after datalogs with similar conditons maintained for both but is it possible that the HTHS of the 10W40 stuff is lower than the Euro oil which could lead to this?
I realize "the mechanic" is likely thinking a 10W40 is thicker than a 5W40 due to a lack of understanding of winter rating/grade which we all know is a thing ("0W is like water bro") and that's what the recommendation was based on.
Edit. I could probably keep this as an ongoing thread as I'm active on many FB groups where folks post some questionable oil-related things regularly.
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