new thermostat...can you bleed the air out?
 

I put a new thermostat in my 300d, with the old one I could not get above 125 degrees unless I was going 70. I already had cardboard over the radiator. With the new one I can't get under 200 degrees unless I am going around 60mph.
the manual shows a bleed screw on the thermostat housing, but it is not there on my car. so.....
-should it run that hot ?( I worry about what will happen in the summer)
-can I/should I/how do I bleed the system? and will it hurt to drill a small bleeder hole in the thermstat like was in the old one?

wheelguru,

I usually try to find a spot to run the car with the nose going up hill, with the heaters on, and the cap off the radiator to complete the coolant system filling. I keep filling the radiator until it stays steady.

By parking pointing uphill (the steeper the better), the radiator becomes the highpoint in the system, and it is easier to get the trapped air to leave the system. I then check the level and top it off after the engine cools and things seem to work ok.

I think you may also have a bum thermostat. Read some recent threads on bad thermostats (one guy got something like 4 or 5 in a row). I would bet if your old set up ran cold all the time, the radiator and water pump are fine, so the fact that all of the sudden you have a hot running engine points toward the thermostat you put in. It should have a little bleed hole that lets air through it so it will atleast open. That hole should be positioned at the high point of the thermostat's seat in the housing to work right.

Good Luck, and I hope this helps a little. Jim

thanks, I like the uphill idea. the new thermostat does not have the little bleed hole, I am thinking about putting one in, but not if I need to return it. -Andy

Andy,

If you take it out to drill it, you should boil it and check the temperature of the water when the thermostat begins and then fully opens. If it is NOT (added by edit) fully open by the time the temperature reaches 180F or 190F, I think you should return the thing as being defective. Boil the old one and see if it ever closes. These thermostats have a two way action, one to let water pass to the radiator to be cooled, and one to mix hot water with cold water coming back from the radiator going to the water pump inlet. This is to avoid establishing a high thermal gradient over the water flow passages, and to avoid a shock when the thermostat opens initially when it is really cold out. It is a little more complex as is nearly everything on an MB (old German saying, "Why make something simple when it is easy to make it complicated?").

So you should notice two sets of travel being initiated at different temps, but the one for opening the path to the radiator should be fully open before the water in the pot on the stove boils.

Hope this helps, Jim