I attached two vertical covers to the left and right sides of the radiator. This will ensure that the radiator continues to function properly. I did it intuitively; I'm not a physicist. But if you cover the entire width of the lower surface of the cooler, I could imagine that an entire working section or temperature range of the cooler would be blocked, because the heat varies from bottom to top and not from left to right. Left and right side added together I covered about 30% (or 40% ?), so the surface area is now approximately the same size as the original cooler. You can test it with different areas to get the best result. For me, this keeps the temperature fairly constant, just like with the old cooler. It is enough for the valve to open. I wouldn't cover any more than that to avoid new problems when driving in warm weather, e.g., in stop-and-go traffic or in a traffic jam.
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