Mine did the exact same thing when it got to 5 degrees. The radiator hose clamps were tight but the hoses were kinda soft. Replaced both upper and lower, leaks are gone even in cold weather. In cold temps, the hoses skrink and expose possible pin holes and as the motor warms, the hoses swell and close the holes as was the case in my particular situation. Hope this helps....

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90 300TE
00 ML320