Look at the following thread and I'd recommend you do what I did. Read post 2

http://www.peachparts.com/shopforum/showthread.php?t=106124

Look after your investment. You're do for a flush and a thermostat is so cheap I'd replace it anyway. Mine failed and caused a coolant explosion:

http://www.peachparts.com/shopforum/showthread.php?t=104716

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz