Are Standard FR4 PCBs Resistant to Ethanol or Is a Special Material Needed?

Does anyone know if standard FR4 PCB's are resistant to Ethanol? Or if there is a certain type that is? I've got a customer who has this specific need and I'm trying to find out. Thanks!

All I can say is I use Ethanol (denatured) to clean the flux off of FR4 PCB (regularly). I soak them for a couple of hours with no adverse affect. And, I have boards that have been in service for over a year that still show no consequence of their exposure to Ethanol.

Now, that's an exposure on the order of hours. If you are talking about prolonged exposure, I have no experience with that.

Also, my testament is not to be construed as an endorsement or a definitive authority. If you want certainty, contact the manufacturer.

if the boards are made from polyester resin based grp, then prolonged exposure to ethanol will break down the binding resin.
i dont know if pcb boards are made from this stuff,

Well the problem my customer has is that the fuel level sending unit in his car apparently isn't playing well with the E85 at the pump. It seems to wear more rapidly. Here's a pic he sent me showing the issue. Apparently this is a pretty big problem and as of yet there is no E85 solution.

There's really no such thing as 'standard FR4'. Contact the PCB substrate manufacturer and the PCB fab house with application specific questions. If you ask 5 different manufacturers for specs, you'll get 5 slightly different responses. The basic electrical characteristics are going to be very nearly the same, but other specifics will vary depending on the type and manufacturer of the epoxy resins, fiberglass and fillers they use. Your board is most likely a Polyimide or PTFE laminate due to the environment it operates in. FR4 resists absorbing liquids but will still absorb some amount of moisture. I'm not in the automotive or industrial electronics industry, so I am not an authority on the subject. Are you sure the material is in the FR4 class?

Also, if this unit is in a car; isn't this a question that should be posed to the auto manufacturer?