It would seem that a copper line could be acceptable IF it was coiled to
flex from vibration at the appropriate point(s).
Or, one could run copper from the gauge to a fixed location in the engine
compartment, then with a fitting run plastic to the engine. I would think it
would be about a 90 degree turn with the plastic. Thus, if it took 9" to get
to the center of the turn from the engine it would seem practical to extend
the plastic equally on the other side of the turn to the copper line to have
a balanced flex. This "hybrid" line would offer the advantages of each line
type (copper/plastic) at the appropriate point. Any "on the road" repair to
the plastic line would not require working under the dash!!! This also
assumes that the copper line from the gauge to the fixed location in the
engine compartment never leaks. Which, assuming a proper installation, -
shouldn't.
Tom Witt
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