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What effect will extreme temperatures have on characteristic impedance of a wire?

My scenario is this: radio equipment controlling an overhead crane inside a steel mill. Specifically it is used for transporting melting pots. With the current, unfortunate installation, the antenna and antenna coax cable are sitting exposed just above the melting pot where it can get many hundred degrees hot.
The coax is a regular RG58 50Ω with copper/tin wire, copper/tin shield inside polyurethane (PUR). These are rated for +80°C but the temperature is _way_ out of specification.
My question is: what will happen with this coax wire in terms of impedance when the temperature just keeps rising? I'm assuming that the metal will expand, but will this have an affect on impedance and therefore also the RF signal requiring an ideal 50Ω?
(As a bonus, there's also a massive magnetic field from the melting process which I assume will get picked up by all metal parts, but lets keep it at one question per post.)

My scenario is this: radio equipment controlling an overhead crane inside a steel mill. Specifically it is used for transporting melting pots. With the current, unfortunate installation, the antenna and antenna coax cable are sitting exposed just above the melting pot where it can get many hundred degrees hot.
The coax is a regular RG58 50Ω with copper/tin wire, copper/tin shield inside polyurethane (PUR). These are rated for +80°C but the temperature is _way_ out of specification.
My question is: what will happen with this coax wire in terms of characteristic impedance when the temperature just keeps rising? I'm assuming that the metal will expand, but will this have an affect on characteristic impedance and therefore also the RF signal requiring an ideal 50Ω?
(As a bonus, there's also a massive magnetic field from the melting process which I assume will get picked up by all metal parts, but lets keep it at one question per post.)

impedance-matching antenna RF Impedance coaxial