Oops , I forgot ! :

Every pound of pressure added to the cooling system raises the boiling point by three degrees, that's for plain water so obviously running a good 60/40 % mix means a few pounds pressure is all you'll ever need .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Btw where are you getting 60/40?
I’ve seen you mention it many times.

I’m running classic 50/50.

__________________
1981 240D 4sp manual. Ivory White.

By experience and from the various trade journals .

I'm sure 50/50 is fine .

I change it every two years rather than by mileage .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

The more water to coolant you have the better the cooling.

In hot climates you can easily run 30% coolant to 70% water because the coolant is there mostly to prevent corrosion

Time has shown tha less than 40 % coolant is a bad mistake .

I also use only distilled water because the local tap water is *very* mineral heavy .

The upside is : local micro beer brewers love the tap water .

My toilet and 1923 kitchen sink, not so much .

I can't get the rust stains out of my 5 year old $uper expen$ive toilet...

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Normal. Nothing to worry about.

When you're in the desert, running AC, traveling what I'm assuming would be around 65, what temps are you seeing?

__________________
1981 240D 4sp manual. Ivory White.

Here is a quote from a non-Mercedes service manual (vehicle has a cast iron engine and uses HOAT coolant):

50/50 Ethylene-Glycol and Water-Is the recommended
mixture, it provides protection against freezing
to -37°C (-34°F). The antifreeze concentration
must always be a minimum of 44 percent, yearround
in all climates. If percentage is lower, engine
parts may be eroded by cavitation.

One more thing to consider: if you aren't measuring your coolant concentration with a refractometer, your concentration probably isn't what you think it is.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

And what's the service interval for coolant in it? Because if it's over 2 years then yes you need a higher coolant ratio.

If you change it every 2 years and you don't let the car sit then 30% antifreeze is fine in hot climates.

I found this manufacturer of coolants saying that minimum they require for all of their coolants is 33%

https://www.peakoil.com.au/automotive-coolants/

Worth checking between condenser and radiator for dirt and leaves. If the electric cooling fan has a shroud, check that shroud as well for dirt and leaves.

Is the hydraulic clutch on the cooling fan still operational? While you are throwing parts at it...

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

on a 240D there is no fan clutch the fan is bolted directly to the water pump pulley

In the Desert at freeway speeds of 65 MPH +/- with the AC on I see 85 ~ 100* C .

It creeps up when I go uphills, never ever reaches the red zone of the temperature guge .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

I probably spent longer than you and tried everything, even removing the Tstat housing to search for blockage (a rag I forgot). My 1985 300D would creep up to 95 C at 2 min stoplights. Of course I tried water pumps (2), T-stats (2), flushed the system with citric acid, flushed radiator, another used radiator (flushed first). Finally installed a new radiator since price had dropped from $350 to $150. No more problems. I tore open the old radiator and found some of the tubes blocked with a thin layer of yellow oxides. I had run a long stainless grill brush across them (in car), but apparently didn't work. Of course my engine could have a slight problem like a cracked head and the new aluminum radiator cools better than the OE copper to hide that.

My 1984 300D had the opposite problem, running at 60 C. A new T-stat fixed that. I tested the old T-stat in a pot of hot water and it seemed to work, but careful testing showed it opened slightly too soon and responded more sluggishly than others in the pot.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Thanks for the replies folks.

I'm mostly within range, just a little beyond.
Whenever I change coolant and flush the system, I always remove the radiator and give it and the condenser a good cleaning.

I do have a fair bit of fin corrosion -or whatever this is called on aluminum. Kind of a gritty, sandy looking oxide on the tips of maybe 35% of the fins.
I don't know how much, if any, efficiency is lost due to this.

At least once a month, I take a nine hour drive up to Northern California.
June-Sept, that means 9 hours at 105C. Yes, it's under red, but it does make me nervous and I keep a hawk eye on these gauges.

__________________
1981 240D 4sp manual. Ivory White.

If there's one MB that can take the heat it's the 240D. Short cast iron head/block makes for a heat resistant design.

If it was my car I'd never drive it like this because sooner or later somethings gotta give. My 2c