Should be fully open at 87-88F. But wait...you said your's was running too cold!! so..it should be opening real early or stuck open. The little ball is a check valve to equalize pressure between the block and radiator. Toss it and get a new one. Boil some eggs instead..

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.