Mine (on a 1989 SL560) failed in the open position, leading to a slow warm up and rarely attaining full normal operating temperature. Not operationally a huge problem except that combustion and oil both work better at full temp, and on a cool morning it took longer than it should for the heater to have anything it could share with me. Don't know details, but as was said above, given German thinking I would expect that failure producing overheating is designed to be less likely.

Bottom line--It's not an expensive part, and should be checked if you suspect it for any reason.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)