Monday, June 18, 2012

E85 Attack on Metals and Rubbers

In regards to the blog title, we are more specifically interested in the materials used inside automotive fuel tanks. (NOT marine tanks) This includes fuel pumps, filters, tanks, level senders, fasteners, wiring, etc. There are tons of disinfomation scattered across the internet on this subject...based on ignorance, misdiagnosis, and corporate interest. So, let's set it straight:

Concern #1: Corrosion

The big concern is galvanic corrosion.  In layman's terms, this is where dissimilar metals are immersed in a conductive solution (electrolyte) that causes at least one metal to corrode.  (corrosion of metal in salt water)  In automotive fuel tanks, we typically have a combination of steel, aluminum, copper, brass, and stainless steel.

The concern is that E85 could possibly have a similar affect as filling your fuel tank with salt water.  In order to analyze this concern, let's look at the electrical conductivity of our suspects:

LIQUID                                           CONDUCTIVITY (S/m, higher number is more conductive=BAD) 
water                                0.0005 to 0.05
seawater                           4.8
gasoline                            0.0000000000000001
E85                                   0.0000000000074
glass                                 0.00000000001

(fellow nerds:  pardon my omission of scientific notation in the table...but I felt the presence of all the zeros helps correlate the relationships)

Indeed, E85 has a higher conductivity than gasoline.  However, it is hardly enough to be a concern.  E85 has similar conductivity to glass, which is often used as an insulator.  Therefore, E85 is not an electrolyte and galvanic corrosion cannot occur.  This is why we don't bother to fool our customers with "anodizing" or "coating" for E85 compatibility with our in-tank fuel modules.  If someone is selling you this, beware.

Concern #2: Chemical Compatiblity with Rubber and Seals

Many hoses and o-rings are commonly made from NBR, nitrile, or Buna-N rubber.  It is cheap and has descent chemical and temperature resistance.  NBR is shown to have "good" chemical resistance to gasoline and E85.  However, in our experience, NBR is not adequate for E85, especially in elevated temperatures in high performance automobiles.

In terms of seals, stick with Viton.  If you're buying o-ring type fuel fittings, make sure they have Viton o-rings.  That is, unless you're okay with risking your expensive motor over $20 in o-rings.

SAE J30R10 Fuel Hose
This submersible hose is generally constructed from reinforced rubber core with a flourocarbon inner and outer shield.  The flourocarbon shields are supposed to "protect" the core from gasoline.  Otherwise, the fuel will permeate (or soak in) the rubber core, causing it to expand and weaken the bond with the reinforcing fabric.  Safe?  Read on:

First of all, the SAE J30R10 hose specification does not include E85.  Let me repeat that:  SAE J30R10 is not for E85.  The ethanol molecule is MUCH smaller than "gasoline" molecules, which allow E85 to permeate easier than gasoline.

Let's assume the flourocarbon shields could prevent the permeation of E85.  Even so, there is no flourocarbon "shield" on the ends of the hose, because the hose has been cut.   If the hose end(s) are submerged, the fuel will permeate through the end of the hose, past the hose clamp, into the pressurized region, causing the rubber to expand, separate from the reinforcement, and eventually lead to failure.

Simple, avoid the use SAE J30R10 hose in E85. 

P.S.  race gas does the same thing to SAE J30R10 hose ;)

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