What are the benefits of using stainless steel oil cooler lines on a Mazda RX-7 FC?

Upgrading to stainless steel braided oil cooler lines on an FC RX-7 is a common and highly recommended reliability modification. Here are the main benefits based on what owners experience with this platform:

1. Eliminating Factory Leaks and Failures The stock oil cooler lines are thick rubber, and after decades of heat cycling, they dry out, crack, and leak ¹¹. In some cases, the inner lining degrades and causes visible bubbling in the hose ³. Stainless braided lines easily handle the heat and pressure of the rotary's oil system, eliminating a catastrophic failure point.

2. Improved Oil Flow The factory FC lines use banjo bolts at the connections, which functionally restrict oil flow. Upgrading to a -10AN stainless steel line setup removes these restrictive banjos and improves overall flow to and from the cooler ⁷.

3. Corrosion and Chemical Resistance If you are running alternative fuels like E85 or methanol, stainless steel lines provide superior corrosion resistance compared to aluminum or older rubber lines ¹⁰.

4. Aesthetics Beyond just safety and performance, stainless lines look significantly more professional and clean up the engine bay compared to the bulky, aging OEM rubber hoses ⁷.

Implementation & Caveats

Difficulty: Easy to Moderate

If you decide to make this upgrade, you have a few routes:

• Off-the-Shelf Kits: Companies like Corksport, Racing Beat, and Mazdatrix sell pre-made stainless kits. However, be aware that some users report premature O-ring failures with the swivel fittings used on certain aftermarket lines, noting that lines with crimped steel fittings tend to last longer ¹².
• DIY / Custom Lines: You can build your own using -10AN stainless hose or have a local hydraulic shop crimp a custom set for you. To connect -10AN lines to the FC's engine block and front cover (1986-1992), you will need metric-to-AN adapters. The FC generally requires 18mm to -10AN adapters ¹².

Safety Note: Always double-check your line routing to ensure the stainless braiding doesn't rub against wiring harnesses or soft hoses, as the steel braid acts like a saw blade under engine vibration.