Rotary Engine Illustrated

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General Information

Evans NPG+ is a special waterless coolant with a 375 degreeF boiling point at zero psi and does not freeze until -70 degreesF (it contracts and gets 'slushy'; not really freezes). Because it is non-aqueous (no water), corrosion is virtually eliminated and there is no need to change it yearly. In fact, it has been tested for hundreds of thousands of miles with no signs of degradation, according to Evans. While the initial cost is high, compared to ordinary coolant, it is a bargain over the life of the vehicle.

Ordinary coolants operate at the verge of boiling, which puts them at high risk of localized boiling at hot-spots within the engine, even when coolant temps otherwise appear moderate. Any localized boiling interrupts heat transfer and potentially creates a cycle that leads to overheating (hot spot gets hotter and hotter, until it gets out of hand). Ordinary coolants also require the system to be highly pressurized to raise the boiling point to the required operational temperature. This puts

stress on all the cooling system (seals, hoses, etc.) and poses an additional risk of a leak that depresurizes the system and drops the boiling point of the coolant below operational temperatures. Evans NPG+ coolant, on the other hand, can be run at zero pressure and has a remarkably high boiling point of 375 degreesF. Because its boiling point is so high, localized boiling is eliminated and overall heat transfer is greatly improved. What you will notice is (1) your vehicle will get up to operational temperature in about half the time, (2) it will then stay right in the optimum temperature zone even when driven well beyond what ordinary coolants could endure.

We have found that most cooling problems in RX-7s are due to overtaxing the coolant, rather than other components of the system, like the radiator. Upgrading to a big aluminum radiator is not usually necessary with Evans NPG+, because the stock radiator becomes more effective using a coolant that better transfers heat. Evans NPG+ is far more cost effective than a new radiator!


Evans NPG+ is non-aqueous, meaning it doesn't like water. It is also incompatible with ordinary coolants. To convert to NPG+, you need to get rid of all the moisture in your cooling system, as well as all traces of incompatible coolant, thus avoiding contamination. The way to do this is to flush your cooling system as if doing a normal coolant change: warm the car up with the heat on (to open the heater core valve), and drain the radiator and engine block. Also be sure to siphon off any coolant in the overflow bottle and/or air separation tank (3rd gen RX-7s). Once the system is thoroughly drained, there will still be some residual incompatible coolant and water. Here, we use an intermediate product that will absorb moisture and is compatible with Evans NPG+: Sierra coolant. Sierra is a "pet friendly" nonpoisonous coolant you can find almost anywhere. Since it is made with Propylene Glycol (like Evans) but is aqueous like Ethylene Glycol (ordinary coolant), it is the perfect thing to do the job. It will absorb any residual moisture and cleanse the system, but any residual Sierra will not contaminate the Evans product. After flushing the system as usual, fill with straight Sierra coolant (no water) and drive the car around for 15-20 minutes with the heat on, then drain and refill with Evans NPG+. Don'

t forget to add some to the overflow bottle, but not too much -- Evans NPG+ expands a bit more than ordinary coolant when hot. The procedure might sound complicated, but it's easier than it seems and is well worth doing. It will also be the last time you need to flush and refill your cooling system as normal preventative maintenance! In the future, if you need to drain the cooling system for any reason, just capture the NPG+ in a clean container and refill when you're done. To convert your cooling system to zero pressure, just remove the rubber seal on the inside of the radiator cap. If you want to run a low pressure system, however, you will need to find the appropriate aftermarket cap. We have found zero pressure works just fine. We recommend, however, that you use the stock, unmodified pressure cap for about a week before converting it to zero pressure. This will help get out any air pockets that might be trapped in the system.

Please note that this is NOT the "long-life" orange-colored coolant, reputed to cause coolant seal damage. Evans NPG+ is waterless, so there is no need for all the troublesome anticorrosion additives used to extend the life of ordinary coolants.

For more information visit the Evans website.
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Copyright © 2005 by Wesley Mahler. All Rights Reserved.