It is a simple device. It has a bulb that sticks into the coolant in the block and it controls a valve, which is supposed to be fully closed at operating temperature. They seem to stick or want to be provide excessive air relative to the coolant temp.

They are expensive to replace.

I have one off a 280SE - I will tinker with it a bit and see if there is anything that can be done to it.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe