This will be a bit long, but I’m providing all the information in case it sheds light on the weird things my engine is doing.
On a recent long trip, just after filling the tank at one of those highway travel plazas (Citgo, in case that matters), my aging Saturn misfired and stalled. The check engine light and the oil system lights came on, and the engine wouldn’t start again for a couple of minutes. I got it started, and it ran strangely, but it ran. Too loud, too whiny, and it didn’t like starting, but at least the car kept moving. I wasn’t too far from the dealership where I bought it, and where the mechanics still remember Saturns fondly, so I took it there. They said the main computer was dying and the mass-airflow sensor was probably dead as well. Fixed the first, which made the second check out as OK, so I went on my way.
The check engine light came on again during the trip home, so I took it to my local garage, the GM branch of a fairly large dealership. After a disturbingly long diagnosis, they told me that yes, the mass-airflow sensor was dead, but also there was too much ethanol in the engine. This is the part that confuses me. According to the mechanic, in spite of the fact that I’ve only used the gas labeled as having no ethanol locally (I live in Iowa, and pay a steep premium for skipping the subsidized corn alcohol), gas companies other than the “top tier” often put ethanol in the no-ethanol gas, and more ethanol than they’re supposed to. Also, crucially, the ethanol somehow builds up in the engine over time. He told me I had 18% ethanol in my engine and fuel system! The car is only rated for 10% at most.
I freely admit that I don’t know cars, but this doesn’t really gibe with what I remember of high school chemistry. How does the ethanol in a uniform mixture of gasoline and ethanol stay behind in the engine and fuel system, thus reaching high concentrations? The claim is that over the years I’ve lived here, the bad ethanol-rich gas has left ethanol behind, so that now, after nine or ten tanks of gas only from the “top tier” companies on this long road trip, and no refill locally yet, it still has far too much ethanol in the system.
The cure is a rather expensive one: draining the entire fuel system, flushing and cleaning it, and adding some top-tier gas back in. Then I’m supposed to buy only the highest-octane gas for a couple of tanks.
Does any of this sound reasonable? Is it just my lack of car knowledge that makes me suspicious? I would be most grateful for any advice.