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Preventive Modifications (Reliability Mods)

Source: r/rx8 community and RX8Club.com — feedback from high-mileage owners.

The Renesis 13B suffers from several known design weaknesses. Owners who reach high mileages without incident almost all apply a subset of these upgrades. None of these modifications eliminate the risk of failure, but they address the most common causes.

:::info Philosophy Owner u/coolbeanzguy123 (148,000 miles, original engine) sums it up (r/rx8): "These cars are unreliable for people who don't take care of them. For people that do take care of them, they are super reliable." :::

Cooling — The absolute priority​

More Renesis engines are lost to cooling system failure than any other cause. (RX8Club)

Low-temperature thermostat (ReMedy / Mazmart 169°F (76°C))​

  • Why: The OEM thermostat opens too late. The temperature gauge doesn't move until the engine is already at 235-240°F (113-115°C), a danger zone for coolant seals and housings.
  • Recommendation: ReMedy 169°F (76°C) thermostat (~$77 from Mazmart) (Mazmart). Do not go significantly below 170°F (CEL, increased consumption, power loss).
  • Note: A lower thermostat alone is not enough if the radiator is clogged. Replace the thermostat AND check the radiator.

Radiator​

  • OEM: The OEM radiator gradually clogs over time, reducing heat exchange surface. OEM replacement (~$150 Mazmart).
  • Upgrade: Aluminum radiator (Koyorad, BHR). Avoid Mishimoto — inferior to OEM and more expensive according to community feedback.
  • Overflow bottle: The original plastic bottle becomes brittle with age. Aluminum bottle replacement recommended.

ReMedy water pump​

  • Why: The OEM pump struggles to circulate coolant at high RPM. The ReMedy improves flow and reduces hot spots in the engine.

Fans — Lower the trigger threshold​

  • The OEM threshold is too high. Solutions:
    • COBB AccessPORT (COBB Tuning) (Series 1): allows programming a lower threshold and monitoring temperature in real time.
    • Mazdamaniac base tune (AccessPORT): includes a lowered fan threshold.
    • Manual switch: toggle to force the fans (effective low-tech solution).

Radiator — Oil line upgrade​

  • The original oil lines run along the radiator and suffer from heat soak (they absorb heat from the radiator).
  • Upgrade: Replace with stainless braided 10AN lines, rerouted along the bottom of the radiator to catch fresh air.

Oil Cooler Lines — Braided Stainless Steel​

  • The OEM oil cooler lines are prone to corrosion, particularly the line in front of the passenger-side front wheel. A rusted line can burst, causing rapid oil pressure loss and catastrophic engine bearing damage.
  • Upgrade: Braided stainless steel oil cooler lines eliminate the corrosion risk permanently. Available individually (no need to buy a full set of three if only one or two need replacing). (Source)

Ignition — The most critical system after cooling​

BHR coils (Bonehead Racing)​

  • Why: OEM coils last ~30,000 miles (Wikipedia, RX8Club) and weaken progressively. Power loss can reach 13.5% (199 → 172 whp recorded).
  • BHR Ignition Upgrade ($580) (BHR Ignition): eliminates periodic replacement, stronger spark. Wires included, plugs extra ($80).
  • OEM alternative: Latest "Rev C" revision coils from Mazmart (~$250). Still better than eBay counterfeits.

Spark plugs — Always OEM​

  • NGK RE9B-T (trailing / upper plugs) × 2
  • NGK RE7C-L (leading / lower plugs) × 2
  • Replace every 30,000 miles along with coils and wires.

Lubrication — Two approaches​

Sohn adapter (Sohn OMP Adapter)​

  • Why: The OMP (Oil Metering Pump) injects dirty engine oil (4-stroke) into the combustion chamber to lubricate the apex seals. The Sohn adapter allows using clean 2-stroke oil instead.
  • Advantage: Cleaner combustion, reduces carbon buildup, OMP lines clog less.
  • Disadvantage: Requires a separate reservoir for 2-stroke oil.
  • Note: Some high-mileage owners (148k miles) drive without the Sohn (RX8Club community), simply doing premix in the fuel tank. Both approaches are viable.

Premix (2-stroke oil pre-mix in fuel)​

  • Why: Ensures additional lubrication of the apex seals. Carbon formed with premix is "softer."
  • Standard quantity: ~1 oz per 2 gallons of gasoline (~1.3 mL/L). Some go to 2 oz per tank as a minimum.
  • Recommended oils (in order of preference):
    1. Idemitsu Premix — considered the best
    2. Amsoil Saber Pro
    3. JASO FC / ISO oils
    4. TC-W3 (acceptable but lower lubricating properties)
  • Caution: Do not confuse with engine oil in the crankcase. Premix goes in the gas tank.

Starter — Series 1 upgrade (2004-2005)​

2kW 14-tooth starter​

  • Why: Original starters (2004 and early 2005) are weak. Mazda upgraded them during production but it was not a recall.
  • Effect: Faster starting, better cranking compression, resolves hot start and flooding issues (per u/mvw2, owner in cold climate).
  • Reference: Upgraded 2kW 14-tooth starter (RX8Club).

Fuel​

Fuel pump​

  • OEM pumps start weakening around 60,000 miles (Series 1). Failure manifests as sudden engine shutdown (pump overheats), followed by normal restart after letting it cool down.
  • Recommendation: Preventive replacement around 60-80k miles. Never let the tank drop below 1/4 to avoid fuel starvation in left turns under load.

Fuel tank — Thermal insulation​

  • The exhaust line runs next to the sub-tank. Hot fuel is bad for the pump.
  • Community tip: Insulate with exhaust wrap or aluminum insulation between the tank and the OEM heat shield.

Summary checklist​

PriorityModificationApprox. costImpact
🔴 CriticalCoils (BHR or Rev C OEM) + plugs + wires$250-580Prevents misfires, power loss, cat destruction
🔴 CriticalCooling flush + 169°F (76°C) thermostat$120-200Prevents overheating and housing warping
🔴 CriticalBluetooth OBD2 for temperature monitoring$20-40Only way to know actual temperature
🟡 ImportantRadiator (replace if >90k miles)$150-400Prevents loss of cooling capacity
🟡 ImportantPremix (Idemitsu/Amsoil)~$15/bottleApex seal lubrication, softer carbon
🟡 ImportantPreventive fuel pump (if >60k miles, S1)$100-200Prevents sudden shutdown, lean spike
🟢 RecommendedSohn adapter$150-250Clean 2-stroke oil instead of engine oil
🟢 RecommendedReMedy water pumpVariableBetter flow at high RPM
🟢 Recommended2kW starter upgrade (S1 2004-2005)$100-200Resolves hot start and flooding
🟢 RecommendedAluminum radiator + fans$300-500Optimal cooling
🟢 RecommendedLower fan threshold (AccessPORT/switch)VariableMore responsive system

What high-mileage owners actually do​

Cross-referenced feedback from owners at 85k-190k miles on original engine:

  • Engine oil: Rotella T6 5W40 synthetic diesel (r/rx8) (burns cleaner, used by RX-7 owners too), or conventional 5W20/5W30 non-synthetic with frequent changes. UK specialist Rotary Revs recommends 10w40 semi-synthetic specifically to improve bearing protection at idle (Source)
  • Oil filter: Some use the Supertech ST7317 (longer than the standard 6607, more filtration capacity)
  • Premix: 2 oz per tank of gas minimum, even without Sohn adapter
  • Regular decarbonization via maintenance ports (see decarbonization section)
  • "Redline a day": Revving high regularly to clear carbon
  • Frequent oil changes: Fresh oil is far more important than oil type
  • OBD2 temperature monitoring at all times