My solution for high coolant temps - 85 300D
 

When I first got my 300D, the temp would stay just above 80 during most conditions, but after a coolant flush and new t-stat, the temps were always slightly higher (90C range). I tried several t-stats from 3 different sources (including MB, which appeared to be the same manf. as Behr) and nothing fixed the issue.

Last week I decided to try a 75C t-stat spec'd for a 116 V8.

The temps have now returned to the 80C range and stayed there throughout my weekend trip to the Central Florida GTG.

The t-stat appears to be very similar in design with the exception of a relief valve? on the outer part.

I'll report back later if anything changes, but I think this has fixed my issue.

http://img.eautopartscatalog.com/hir...300&height=300

I suspect that you caused more of an issue than you resolved. An 80 degree thermostat has a normal operating range of approx 80 - 95 degrees. It doesn't sound like you had an issue with the correct thermostat.

i am always around 90, i think its normal

i removed the A/C rad from infront of the main rad, only the egt's went down 100 degrees for all around driving, water temp is the same

what issue have I caused?

when I say coolant flush, I mean a coolant exchange with a water rinse. I didn't do a citric acid flush or use any other chemicals. it had the green stuff when I got it.

I think the only issue that you caused was more work for yourself than needed. Operating temp of 90C is pretty normal. Anything between 80-90C is pretty normal when you start operating much below or above that you have issues. My wagon runs a 90 all day long, while my 240 is closer to 80.

You installed a thermostat that will cause your engine to operate at a temperature lower than specified. It may seem logical that cooler is better; it isn't necessarily that way.

I've installed a t-stat that makes my car operate at the same temperature it did prior to switching it from an older Walher to a modern Behr.

The question
 

is how many years and/or miles has your radiator been in use?

unknown. I don't have any records that indicated a replacement, but most of my service records are for the routine stuff not repairs.

IMHO, to adequately flush the cooling system one must install
a prestone back flush kit. the "T" installs in the heater hose
coming from the fire wall. then....

1. loosen the top radiator hose from the top of the radiator. take a small oil cap (available from a car parts store) and plug the top radiator inlet. be sure to rest the radiator hose on the top of the radiator.

2. connect a garden hose to the "T" connector and turn
on the water full blast. run the water until it runs clear coming
from the top radiator hose.

3. do the diesel flush sequence shown on dieselgiant.com use the Shout
Ultra Gel mixed in two gallons of warm water. put this mixture into the radiator. tighten the hoses, remove the "T" connector from the garden
hose and close the system. start the car, run for 15 - 20 minutes
with the heater turned on high. afterwards, drain the water from
the radiator and then reinstall the drain plug. perform steps 1,2
above until the water coming from the top radiator hose runs crystal clear.

4. perform the mercedes benz citric flush. afterwards, perform steps 1- 2
above until the water runs crystal clear.

5. if you are unsure about the age of your radiator I recommend purchasing a new Nissens radiator with the improved design. you don't know the age of your current radiator. what if the transmission cooler barrier fails and the old radiator dumps coolant/water into your trannie?
now THAT is an expensive failure. makes the cost of a new radiator
look cheap compared to a transmission replacement.

6. LAST but not least is this: regular green antifreeze does not provide
sufficient cooling capabilities for a diesel engine. diesels get hot and
require an antifreeze SPECIFICALLY rated for diesel use. a lot of mechanics do not know this and will put green stuff in a diesel. WRONG.
either use Amsoil antifreeze which is rated for 750,000 over the road diesel use or Cummins Diesel has a special antifreeze for diesel engines. either
will get the job done and keep your engine running cooler. not using coolant specifically formulated for a diesel engine will shorten the life of your engine, I GUARANTEE IT.

7. use the stock thermostat, diesels run a little hotter than their gasoline
powered counterparts.

When you buy new tires, do you make sure they match the tread depth of the old ones?

when you comment on posts, do you try to be a jerk?

if you were to poll w123 owners here, I'd bet you'd find many who see operating temperatures just north of 80C, which is where mine was at before I changed thermostats.