Why shouldn't I use Evans NPG+ waterless coolant in a Mazda RX-7 FD?

While waterless coolants are popular for their high boiling points and zero-pressure capabilities, there are several distinct drawbacks and reasons you might decide against running Evans NPG+ (or its modern equivalent) in your FD RX-7:

• Higher Operating Temperatures: Running straight coolant without water can cause the engine to run hotter and be less efficient. Oil and water temperatures can easily rise by 5°C, potentially robbing the engine of around 10 horsepower ¹.
• Complex Installation and Bleeding: Converting to Evans requires meticulously flushing out all water from the cooling system, often using a prep fluid. If the remaining water content is not kept below the recommended minimum—which must be verified using a refractometer—it will create an acidic byproduct and become highly corrosive ¹. Furthermore, bleeding the thick coolant with a mechanical water pump is difficult and requires multiple heat cycles with the vehicle positioned at different angles ¹.
• Viscosity and Flow Restrictions: Evans has a much higher viscosity than standard coolant. Because it is thicker, you must drill a couple of 1/8-inch holes in the thermostat to ensure the fluid keeps moving while the engine is cold ¹.
• Zero-Pressure Circulation Issues: Evans is typically run with a zero-pressure cap, but the FD's complex cooling system was designed to flow under pressure. Without pressure, the coolant tends to take the path of least resistance, which can prevent it from flowing adequately into smaller side pathways like the thermowax ¹.
• Loss of Visual Overheating Warning: Standard coolant boils and creates steam when overheating, providing an immediate visual warning to shut the engine down. Because Evans does not boil or steam, you lose that early warning sign in the event of a catastrophic failure, such as dead radiator fans ².

As a final note on product availability, Evans no longer manufactures the original "NPG+" formulation. The correct direct replacement for street applications is their "High Performance" (HP) line. The standard "NPG" currently offered is recommended exclusively for racing and is not intended for general street or daily use ¹.