Reminds me of a case stuck in my mind that I never solved. About a year ago we were going to change the rear end gear oil on our 2013 Dodge Charger. That went well and then decided to only check the oil since it was just past 3k and we change that one at 5k due to lots of short trip driving. The oil on the dipstick looked like a burnt corn dog = very thick and black for the miles on an engine with only 48k on the clock.
The oil was 5w20 Castrol magnatec - we had some more so proceeded to change it. This was the strongest I had ever smelled gasoline - eye watering (car used E10 regular) - yet, again the oil was very thick.
I kind of wrote it off for "washing" effects and took it to the dealer to discuss. Diagnostics came back fine - no fuel or engine issues. We just started changing the oil at 4k going forward due to 90% "town" miles and how many months it took to even get that.
From Amsoil
Why is fuel dilution a problem?
•Reduced oil viscosity interferes with formation of a durable lubricating film, inviting wear. It also negatively affects the oil's ability to function as a hydraulic fluid, which is critical in engines with variable valve timing
•Fuel can wash oil from the cylinder wall, causing higher rates of ring, piston and cylinder wear
•Reduced effectiveness of detergency additives limits the oil's ability to guard against deposits
•Increased oil volatility results in higher oil consumption, requiring more frequent top-offs
•Accelerated oxidation reduces the oil's service life and requires more frequent oil changes