For best Evans Waterless Coolant results, should I use a pressururized or non-pressurized radiator cap on my slant six?

Keep the coolant recovery tank?

Thanks very much for the wisdom & experience.

--Walt Jackson

One big advantage of the waterless coolant is that the cooling system operates pressureless, which means a lot less stress on every seal, gasket, and hose. Doesn't really matter what the cap's pressure rating is; once the last of the residual water is purged out the system (by burping off the pressure after the first half-dozen times the engine reaches operating temp), there will be no further pressure buildup in the system. No water, therefore no steam, therefore no pressure. Keep the coolant reserve system intact, and make sure your cap is the proper kind for use with a reserve system.

More info here.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

from their FAQ

Over time, will Evans coolant absorb water?

Evans waterless coolant is hygroscopic, which means it has the ability to absorb moisture. As such, containers of unused coolant should be kept tightly closed. In the cooling system, Evans waterless coolant should not absorb a significant amount of moisture from the atmosphere as long as a conventional pressure cap is used. Under normal circumstances, the cap should not open, allowing air to enter the system.

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1970 Barracuda 225 /6, 3spd on the floor, Blue/Blue