Pay heed to what Sixto had to say. 80/85 is not at all unusual. If its boiling while you see either of those values on the temp gauge, your gauge way be out of wack or the temp sensor on the cyl. head is faulty, causing an incorrect gauge reading. I would also consider what 97 SL320 had to say in post #4. This overheating may have blown your head gasket.

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"