Where is the coolant leak coming from on the driver side of my Mazda RX-7 FD?

Difficulty: Easy to Moderate

If you are tracking down a coolant leak specifically on the driver side of your FD RX-7, there are a few common culprits you should inspect:

• Engine Coolant Drain Bolt: If the coolant appears to be dripping down the driver's side of the subframe, check the engine block coolant drain bolt. It is easy to overlook or leave slightly loose after a coolant flush, which will cause a slow drip in that exact area ¹.
• Plastic Overflow Tank: Inspect the plastic coolant overflow tank. These are notorious for cracking as the plastic ages and goes through heat cycles ⁵.
• Radiator Hoses: Double-check the upper and lower radiator hoses, as well as the line running to the overflow tank, to ensure the rubber hasn't split and the clamps are tight ⁵.

How to find it: Because coolant can travel along subframes and hoses before dripping to the ground, the most effective way to pinpoint the source is to use a coolant pressure tester. You can usually rent one from a local auto parts store. By pressurizing the system while the car is off and cold, the tester will force coolant out of the exact leak point without you needing to run the engine ⁴.

Safety Warning: Do not drive the car until you have located and repaired the leak. A small, unknown coolant leak can turn into a major leak in an instant, which threatens to rapidly overheat your engine ⁶.