New thermostat or not?
 

Got a new thermostat on hand. Will be doing a coolant change soon. Wonder if I ought to change the thermostat now or just hang onto it and use it when the time arrives. Have no idea how old the one in the car is - it could even be original. The car stays at a rock solid 82°. This is the SL I"m talking about.

change it for peace of mind.

My suggestion:
Don't try to fix what's not broken.
:)

New thermostat or not?
 

Not.

Do not change it.

No harm in changing it while the coolant is out. I usually change mine during coolant changes.

Change it if the new one is OEM. At $5.00 a pop it's not like your throwing too much money around... and your fresh (orange) coolant and system will have an even fresher start. Don't forget to drain the block ;)

OK, I'll bite. Where do you get OEM themostats for $5.00?

Ooops. I guess my memory is fading faster than I thought. Ok $28.00 is a little money to chuck. I guess that I wouldn't throw the 28 at it unless it was running out of spec, which it appears not to be. Thanks for setting me straight... I put one in the 300E this summer as part of a large part order including rad hoses and radiator and could have sworn it was cheap... guess I have to start eating more fish. ;)

But still remember to drain the block.

$21.37 for Mercedes OE thermostat. I plan to drain the block. There are supposedly two drains, one on each side. Hope they are reasonably accessible.

Thanks for the replies. It's almost a tie. I'm leaning to changing the thermostat, since I've already got it in hand.

I just replaced mine recently at around 98K miles on the M113 engine. It makes teh engine run a few degrees warmer in the cold weather, but I can't say whether it's significant. Before it was always spot on the 80C hash mark, and now it steadies out with the needle covering the top loop of the "8". That should be 87 degrees, but I would think 87 is a bit higher on the gage, given that the next hash mark should be 100.

The only reason I bothered to change it was that I was seeing a lot of creamy oil goop under the oil filler cap, so I figured warmer oil may help to burn off any condensation. But I can't say yet if these few degrees make a noticeable difference.