"Dissing" Dissimiliar Metals

I want to replace my rusting fuel and evap cannister steel lines with non rusting, copper refrigeration tubing. CUNI would be rather pricey, I’m told. But to avoid the dissimiliar metal oxidation that occurs with readily available steel flare nuts, I would have to try and find the brass flare fittings I’d need to splice into non rusted ends of tubings. Don’t know if this would be a difficult search or not, finding the 5/16" brass flare nuts I’d need, and the fuel filter fitting would be a very common 3/8" size, but the male flare nut threads would have to be metric. But I was wondering what chance I’d have to insulate copper tubing from steel flare fittings if I had to use steel flare nuts, using removeable grade thread lock between copper tubing and flare nut?

I wouldn’t trust copper to withstand the pressure and vibration of a modern, high-pressure EFI setup: it’s a much softer metal than steel. Other than having a ready supply, is there a reason you don’t want to replace with like metal?

I’m all for “redneck repairs,” just not on fuel and brake lines.

Water lines use a dielectric coupling when joining dissimilar metals, I doubt it is worth the risk. Go with standard technology, imho.

You could use stainless steel instead of carbon steel.

thanks for advice, i should plan to use stainless or CUNI even at high cost.

I’d just replace it with exactly stock materials. The corrosion that occurs with dissimilar metals can be quite rapid. I’d rather have to replace it again in a few years, and I might try protecting it with paint.

How long did the original lines last?


You’re messing with the fuel and emissions systems

If the smog technician sees what you did, you will very likely fail the visual portion of the test

These will be the reasons

Emissions device removed/altered
Emissions device shows evidence of tampering

Personally, I think you’re overthinking this

Replace the evap components with the correct parts and crack open another beer . . .

Afterwards, of course

texases, the fuel supply, return, and evap cannister purge line are original and have been in 13 years, it’s a 2000 Century

again, thanks for all replies

Some of these auto repair stores sell a composite type of corrosion resistant high pressure metallic line now-Kevin

If the original lines lasted 13 years, I’d just replace them with stock materials. If you’re lucky, you’ll have to replace them in another 13 years. Odds are the car won’t last that long.

makes sense, texases, thanks. Kevin, are you referring to CUNI tubing?

Dont know what they call it,just happened to see it at a parts store the other week-Kevin

Kevin, CUNI=Copper Nickel

Why are you looking to over complicate a system that has been working near trouble free for decades on vehicles of all types. If you are dying for something to repair…take an icepick and poke some holes in your tires and then locate the holes and plug them up…sit back and enjoy the satisfaction of a job well done.

One other consideration why copper may not be the ideal solution. Copper has a unique failure mode, to develop pinhole leaks. This is more likely to happen when running water in copper tubing probably, but one thing you definitely don’t want is a fine spray of gasoline in a hot engine compartment.