I've used Mobil 1 0W-20 syn from the beginning (64K miles now). Yes, I now do a lot of shorter trips / local, but from 2011 to 2015, I did drive 30 mins each way or longer on highway at 60-70 mph and still had an increasing oil level over the duration.

I haven't seen evidence of a oil / water / coolant emulsion (milky). Car never over heated and in 2014, I changed out the coolant (FIT & a CIVIC) with new Honda juice. All was OK there.

The oil appears to "age" properly through the cycle, which I think is way too long (Maint Minder at 20%-30%) when I change filter & oil around 6000 miles (live in Pennsylvania, so I time the change out so I'm not laying in snow when the MM alerts me). I change oil on 3 motorcycles and 2 cars, so I'm frequently looking at used oil (collecting and pouring into a recycle bucket). The FIT oil doesn't appear to be any different than the others.

As an example of my driving style, I'm still using the original front brake pads at 64k. Wife's CIVIC has 109K and is on the 4th set of pads f/r - she scares me when I'm a passenger.

The only problems I've had with the FIT were loose #2 & #3 spark plugs, which are fixed (blue Permatex threadlocker), some valve noise, and occasional mouse nesting problems on top of the cabin air filter.

Local gas mileage is hovering around +/- 30 MPG (calculate after a fill-up on a Sport AT), but when one or both spark plugs were loose, it was 23 - 26 MPG (could smell gas in passenger cabin) with highway driving. So, I'm kind of thinking that the plugs are doing their job.

Obviously, oil consumption would represent a bigger problem then a curious increase in oil levels, albeit small, over 6000 miles. If there is some sort of dilution occurring, changing the oil out before the bitter end (~10,000 miles per cycle) should give me some protection.

 

I suppose you could send an engine oil sample to laboratory to see if anything alarming is within it, but I agree that your attention to good maintenance ought to reduce any concern.

You and I drive much alike -- I get very long life from my brake pads too. Thinking ahead saves braking and contributes to good fuel economy too.

 

Quit guessing, Pull an oil sample and send it to Blackstone Labs in Fort Wayne, Indiana. They will tell you gas, coolant, or water content if there is any. Try to take the sample just before an oil change. If that is a long way off then take it now and note the number of miles on the oil sample when you send it in.

Blackstone Labs

 

The local Caterpillar equipment dealer does that sort of work for $15 / sample.

 

No, you were driving around will little trans fluid...and too much oil.