Defective WRD Thermostats

[mistral66]

I have tested three new thermostats so far for my 280SL and all have proven defective (one from Parts Geek, and two from Authentic Classics). All of these Mahle thermostats have had exactly the same problem: the pin refuses to budge once the retaining clip is removed and the pin refuses to rotate. My understanding is that the pins should spring out immediately once the clip is removed and put tension on the WRD plunger assembly once installed. George at Authentic Classics very kindly replaced the defective unit immediately, but I am concerned that the current inventory of these thermostats will have much the same problem. Can these thermostats be restored with heat or WD-40?

[mrfatboy]

How did you test? Does the pin move when thermostat is placed in a pot of 180 F degree heated water?

[mistral66]

Yes, you're absolutely right, Immersing the thermostat in hot water did the trick and wonder of wonders it loosened the pin. I fitted this thermostat inside the WRD with the pin extended, putting pressure on the plunger and on the disc inside the injection pump. I also sealed the edge of the adapter ring to prevent water entry into the injection system. I still have to reconnect the WRD coolant hoses, but everything should work great now. Again, thanks for the help!

[enriquegarcia]

Mistral66: All those thermostats may be perfectly fine. My understanding is that there are no springs internal to the thermostat, only wax, and the pin does not (and should not) pop out when the temporary retaining clip is removed. (I guess the temporary clip is for added safety during shipping?) The sure way to test one, as was noted, is to dunk it in a pot of boiling water and watch the pin slide out. BTW, when it cools the pin will again retract even with no pressure applied to it.