PeachParts Mercedes-Benz Forum - View Single Post

JimSmith · #2 03-08-2003, 11:05 AM

rickjordan,

When the car was new, and probably for a decade or more thereafter, it likely ran at about 80 degrees C or just a hair less.

Others on that frequent this site have noted in the manual that it says it is ok to run up to the red zone without damaging the engine. That may be true, but I believe there is some system degradation when the car starts running at 90 or 95 degrees C.

My Diesels have always had the needles seemingly glued about a needle's width below the 80 C mark, regardless of outside temperature and load when all is well. If my cars run hotter than this I take it to mean something is not correct, somewhere, something changed. With the simpler models, the W123 and earlier 240D and even older 220D, this was never more than a bum thermostat, leaking radiator cap or leaking water pump. The newer models have some complications with fan operations and automatic climate controls. I have not had the pleasure of having to dope these out yet on one of my cars, so I am not much help there.

So, I would figure, since the system used to be able to hold you at 60 degrees C, that the part you put in to regulate temperature, the new thermostat, is either faulty or somehow the installation was faulty. These thermostats are a little more complex than the average, as they have two sets of moving parts to control flow bypassing the radiator and flow returning from the radiator. Also, the system is pretty sensitive to venting, and any trapped air can cause problems with the operation of the thermostat.

So, I would try to make sure the system was fully vented. I usually do this by parking on a pretty steep uphill rise (which I have in my yard), with the radiator cap at the high point (right side of car more uphill than left). Then I fill the system, run the car with the heat on full and the radiator cap off until the temps get to their normal maximum temps. I fill with MB antifreeze and distilled water until the system takes no more, then I squeeze all the hoses a few times and do the filling exercise again, until it will take no more fluid.

By the way these thermostats go in one way, and they usually have a little vent hole that is aligned with the high point in the housing. With a bubble of air or steam on one side, thermostat will have a great deal of difficulty responding to the hot side water temperature.

I hope some of this helps, Good Luck, Jim