Some of you may have followed my 7 week journey of why both my 525efi engines failed me at the same time, on two of three last trips out on the water. After extensive step by step replacements, the smoking gun was my fuel line (separate for each engine) that had deteriorated from the inside and created a 100% blockage for port and about 70% blockage for stbd. Both since changed, and boat is running better than ever!

So, my question is, I have access to Ethanol Free fuel, its about .50 a gallon more than Reg Unleaded, is there anything I should be concerned about should I make the switch to Ethanol Free? At the pump, the octane rating is 91, so higher than reg unl at 87. I did call Mercury, and they said nope, all good, and the engines will love it. In fact, he said they build their engines to withstand up to 10% ethanol blend, but in my case it was the boat manufacturer side that failed, fuel line from tank to Mechanical Fuel Pump, (granted, after 14 yrs...my boat is a 2007).

Probably just a rhetorical question, but tossing it out there anyway for comment. Anyone else out there running pure Ethanol Free?

Thanks all!

I never run ethanol fuel in my boat, pretty sure the 525 is set to run on 87 running a higher octane doesn't mean the engines will like it

In short all good except the 91
The 91 will not provide as much power as the 87, so you might have some black build up around the exhaust
Agree all new fuel lines will not have an issue with E10
Using E0 means no need for stabil

Never ran ethanol fuel in any of my Mercury's 280, 300PM, 300xs outboards... and now 496HO. Only have 1 off water station selling "free" for 4.50(90 octane) and on water at marina 5.50(87octane). Never had fuel related issues since 1999. I'm lucky marina lets us bring fuel to dock which I do with 15g buggy.

525 EFI's are set up / tuned for 87 octane fuel and will run fine and strong on it. Higher octane fuel will burn cooler, make somewhat less power / unless retuned for it ie. the Whipple recal / I have run it all for more than a decade and have found that they are very happy with just plain old 87 pump gas. Just treat it properly when putting it up for the off season and you will be just fine.

P.S. I have seen the inside of my motors after 340+ hours and they looked just fine.

Working on many seasonal things for ne, friends snd family, and customers i made a rule of thumb that e10 is okay for about 8 months. Reason for this i have not fun into any issues under 8 months, plenty over it. In fact, one today. Holley carb ford motor older Ski natique.

Been buying 93 Non Ethanol from Walmart. Has been available for around a year here in SW FL.. It is up to $3.689 per gal though.

If it “works” or “plays” I don’t use ethanol in it, the daily driver, I don’t have a problem with using it

I avoid ethanol at all costs. My 502MPI's vapor lock with ethanol. Premium runs rich as well. 87 best for me.

Same here in Pensacola/Orange Beach.