E85 Can Mess Up Your Engine!

Although E85 is an awesome fuel, high octane, cheap, cool burning, it can cause a lot of harm under certain operating conditions.  This is an EJ257 that failed in my daughter’s car.  When she was in high school, she only drove about 1.2 miles to her school from a cold start and after the car sat all day, then she drove the same distance home.  Because of the short drive cycle, the engine never really got warm.  I knew that E85 makes a lot more moisture than gasoline and was concerned about oil contamination from the mixture of blowby, E85, and water and had upped the oil change intervals to every 2000 miles with high-quality synthetic.  Suddenly the car developed a lot of blowby and a loss of compression, I assumed it was a typical blown Subaru engine and yanked it out and it sat in the corner for a few years.  Last week we decided to take the engine apart to see if it was any good to use as a core engine and we were amazed at what we found!

First off the pan was filled with a black tarry sludge, the kind you find in neglected engines, not ones that had the oil changed this frequently. The moist running E85 had created a ton of milkshake in the oil and with a big radiator and oil cooler, the engine never got hot enough to boil the water off so it coalesced into the sludge after time.

The underside of the cases had some varnish but it was not too bad, this shows that the oil was changed.  The top end of the engine looked like new with no varnish or anything.


  1. GD STi stands for for something else in this case, lol. Love your transparency with the EJ. I’ve pondered doing a straight E85 tune in my Subaru, but now I really don’t want to.

  2. I’d recommend oil analysis if you really want to know what’s happening in an engine. It would have detected this contamination well before the point of being catastrophic and is more cost effective than frequent oil changes.
    I don’t work for, nor am I compensated by, but have used Blackstone for 2/3 current cars and will do so for every vehicle in the future.

  3. Hi, excellent article.
    Not just E85, driving an cold engine ruins it. It does not matter with E85, regular gas or diesel – the result is the same

  4. Looks like my Prius Prime oil cap during winter. As it will mostly run as an electric car, it uses the engine in short bursts when the battery is depleted. The oil definitely doesn’t like that so once or twice in a week, i run a 40 / 50 miles trip just to bring it at full operating temps. A non issue during summer as the battery has more then enough capacity for my errands and i use the good old (2012 witk almost 500k km on the clock) Civic Si more.

  5. ’07-’09 VW GTI’s were notorious for this because of bad thermostats. The dealership would tell people to take the car for a 60 mile drive once a week. Or change the stat yourself and everything is fine.
    I saw some horrific sludge mess in engines at the dealership.
    Pulled valve cover of a SBC in a Blazer, ticking lifters/valve train noise. The sludge was a perfect reverse mold of the valve cover with little opening for each rocker arm.
    Seized BBC in a truck. Pulled oil drain plug, no oil came out. Removed oil pan, It was heavy, pan is full of congealed oil, but there is a hole in the oil, where the oil pump pickup was. Slide under truck and there is a tower of congealed oil sitting on top of the oil pickup screen. To this day one some one dumps out a can of cranberry sauce I think of this truck. We call this stuff “Can”berries. I can’t eat them.
    Lastly there was the BBC that was gummed up so bad most of the pushrods would no longer feed oil up the the rocker arms.
    All three got new engines.

  6. Hi Mike,

    I have a question, our STI is E85 and one injector get stuck opened. A good amount of E85 went to the engine oil. We are waiting for new injector, but what you recommend? Change the oil quickly? I dont know if the E85 in the engine oil can damage the engine.



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