Engine fire wall?

[SnowDrift]

PTFE is the correct choice in my estimation when replacing factory steel on those and the engine oil cooler lines. The temperature rating and pressure rating make them the best option from my research.

 

[dieselolds]

I would do away with the factory GM connections. they can pop out and leak on you. most aftermarket coolers are female NPT thread so you can use most any standard fitting. run you a hose barb connection from the cooler around to the one in the radiator but use a good oil cooler type hose that can handle the temps. for the steel trans lines, use a flaring tool to make you a barb on the end. then slip on the hose and clamp it. the flare type barb is to keep the hose from coming off!

Definitely can’t beat npt fittings