Flash point and vaporization temp are not the same thing. Gasoline or rather certain components of gasoline start to boil around 100C. Which coincidentally or not is the temp around which most engines keep the oil temp.
Fuel dilution - 1.9 mile commute. Let idle before leaving?
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Flash point and vaporization temp are not the same thing. Gasoline or rather certain components of gasoline start to boil around 100C. Which coincidentally or not is the temp around which most engines keep the oil temp.
Interesting. Does this translates to “getting the fuel out” or just being better than not doing it?
Most engines have a cold start at least once a day. Cold starts are the worst for fuel dilution. Cold engine, cold fuel, cold air are not conducive to vaporizing fuel, which is what burns not the liquid gasoline itself.
Take two identical engines, one started and driven for say 45 minutes at highway speeds, another started and short tripped for say 10 minutes. If that exact cycle was maintained throughout the OCI, you would see much more fuel in the short tripped engine.
So compound multiple short trips on a cold engine, every time you start the engine cold you are dumping fuel into the oil. So the effect can compound in the sense you haven't burned off the fuel from the first cold start of the day, then latter in the day you start it again and dump more fuel into the oil.
Some engines are more prone to this than others, but every engine does it to a certain extent.
I agree, take the long way to work every other week. Don't let it cold idle very long. You are doing well, considering the circumstances.
My extensive UOA testing on several vehicles from years ago suggests to me that once dilution occurs, no amount of normal usage will mitigate it. Enough of the fuel constituents will remain to show up in the oil. I suspect that one reason for this is the modern automobiles I have owned seem to be designed to run somewhat "cold." (Perhaps as a method to ward off heat degradation and prolong oil life.) Some of my vehicles would only register 212°F oil temp during extremely hot weather in stop and go traffic. Normal oil temps would generally be below 190°F. And it took at least 30 minutes for it to get there. Sure temps at some hot spots would be more than that but evidently not long enough to have the desired effect.
My take, gotta live with it and do shorter intervals. It is called severe service use.
Take the long way home a couple times a week.
We get more diluted samples nowadays because of direct injection being commonplace.
Walk, or ride a bike 
Your engine will be spared wear and carbon build up and you'll do some exercise.
Your engine will be spared wear and carbon build up and you'll do some exercise.
So could taking it for a long drive fix that then?
Less likely than if the dilution is due to typical short-tripping in cold weather.
Shel_B
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I should have mentioned that my car is port-injected, so fuel dilution is not an issue for me.
SammyChevelleTypeS3
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What I can not get over with ours is that even with keeping up with the routine flushing and fresh coolant, plus the engine temp gage never seen reading higher than normal , the amount of heat this engine throws off once shutdown and parked in the garage. I often open the hood once we park it to try to dissipate some of that heat quicker. A retired Honda tech and a couple guys I knew with their own Indy shop told me they did this with some of their personal vehiciles.
Ok. It seems to me the just take it out for a long drive recommendation doesn’t really help anything unless under certain conditions.
I think the OP’s NB Miata has port injection.
Where did you have it tested?
You are doing fine if you are getting it up to temp relatively often.
No need to do anything out of the ordinary.
Change the oil more often, problem solved.
Take it for a 30min highway drive once a week or change it earlier.
It's a bit self-indulgent to drive a gas car 1.9 miles, compromising its longevity, then complain about fuel dilution...and you have the option of driving your EV. The Miata is a fun high performing car, yet you ignore that mission during your drive to/from work. You are wasting a nice set of wheels, here.
I find your question and reasoning irrational...a 1st world problem I guess...
I find your question and reasoning irrational...a 1st world problem I guess...
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