Mazda RX-8: Renesis Engine Flooding on Hot Restart

The 13B-MSP Renesis rotary engine is highly susceptible to fuel flooding when attempting to restart a hot engine that has stalled or been switched off briefly. Rotary engines have inherently low compression ratios (8.5:1) and rely on high cranking speed to achieve ignition. When the engine is hot and a restart is attempted but fails to fire on the first few cranks, the direct-injection and port-injection systems continue to deliver fuel. Because the engine is already at operating temperature, fuel vaporises partially in the pre-chamber but does not fully combust during failed cranks, leading to liquid fuel accumulation in the lower rotor housing and exhaust ports. Continued cranking to overcome flooding further wets the spark plugs (the RX-8 uses two plugs per rotor face — leading and trailing), causing them to foul. Attempting to clear a flooded rotary using the standard Mazda clear-flood procedure (wide-open throttle, crank for 20 seconds, rest 2 minutes) can drain the battery if performed multiple times. Repeated flooding events accelerate apex seal and spark plug wear. This is a design-inherent limitation of the Renesis noted widely in Mazda workshop documentation.

• Engine cranks but will not start when warm
• Strong fuel smell from exhaust during cranking
• Spark plugs wet with raw fuel after failed restart
• Battery drains from extended cranking attempts
• Engine eventually starts with WOT clear-flood procedure

1. 1

   Inspect spark plugs for fouling or oil/fuel contamination — both leading and trailing plugs per rotor should be checked.

2. 2

   Ask seller to demonstrate a hot restart after a brief stop.

3. 3

   Check battery health as repeated flooding events drain batteries.

4. 4

   Inspect exhaust for fuel smell residue inside tail pipe.

$150 to $800 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the car ever failed to restart when the engine was warm?”
• “Has the Mazda hot-restart procedure (WOT crank) been needed regularly?”
• “When were the spark plugs last replaced, and what was their condition?”
• “Has the battery been replaced recently, and why?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.