The rate at which the temp drops after the t-stat has opened is a function of how fast it opens at rated temp. If it starts to open at 90, your temp may go up a bit higher then drop as the stat fully opens. If you want to experiment. Take out the stat and see what the max temp is. You're in a warmer area of the country so this shouldn't be a problem. Some open slower than others. If it does drop back down to 88-90, then you're OK. Be happy, don't worry.

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Jeff L
1987 300e
1989 300e
1987 BMW 325