And there you have it : this is called "Solder Bloom" and if you can see it, it means the radiator isn't yet clean .

Either spend some serious time and effort or just buy a new one .

This is *exactly* what my 240d had, as I've said before it took me a long time to get it fully clean .

-Nate

Shern wrote :
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.

Adding to Tangofox's observation.

https://www.amazon.com/Antifreeze-Coolant-Refractometer-Automobile-Windshield/dp/B07DLDZFJX/ref=sr_1_11?_encoding=UTF8&c=ts&dchild=1&keywords=Lab+Refractometers&qid=1623196047&s=industrial&sr=1-11&ts_id=393272011

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Are we talking about the same thing?

This is on the exterior, not the interior of the radiator.
The fins.

Unless you're suggesting there's a correlation and that the exterior bloom is caused by interior corrosion (that would be a stretch for me, but I'm open to it).

EDIT: after a quick google, it appears solder bloom can only occur on copper or brass. I think we're talking about a different issue.
This is my rad:

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1981 240D 4sp manual. Ivory White.

Unless I've got you wrong, you're saying two things here: The 240D can take the heat, but you wouldn't drive it like that?

I'm definitely not happy about it and would much rather err on the side of caution, hence the post.

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1981 240D 4sp manual. Ivory White.

I missed that part Shern .

I'd still be wary of any corrosion anywhere .

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-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

Yes that's exactly what I mean.

Sure, but I see no correlation between the two.

Did you see the photo?


I'm with you.
New rad it is.

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1981 240D 4sp manual. Ivory White.

Actually, it doesn't appear the specified minimum concentration for all of the subject coolants is 33%. The minimum for one appears to be 50%.

Since Zerex G-05 seems to be a preferred formula for Mercedes diesels, maybe we should be looking at what Zerex recommends.

https://sharena21.springcm.com/Public/Document/18452/f93a8057-fe75-e711-9c10-ac162d889bd3/c264d227-0dbd-e711-9c12-ac162d889bd1

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Follow the directions ! .

As I said : 60/40% and don't use tap water .

Shern : for some reason the photo didn't show before, now I understand you're talking about exterior fin corrosion .

It doesn't look bad to me, I'm betting there's still crud inside the water jacket ~ it took me over a month of repeated flushing with citric acid and distilled water before the crud stopped coming out ~ I had a 30 + mile freeway drive to work then and I'd begin the day with a fresh load of citric acid and water, by the time I got to work the coolant wasn't translucent anymore so I'd drain it and flush it all out including the 17MM block plug behind the blistering hot exhaust manifold, drain the plain flushing water out and refill with new citric acid and distilled water...

In time it took several days for the mix to turn cloudy, then I knew I was getting there finally .

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-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

You can crack the block if you pour in cold coolant into a hot engine. And burn yourself.

But I agree about flushing the engine because I've seen a few cylinder heads with plugged coolant passages.

Wow! That’s tenacity. You must have had a very gunky system.
A month of citric flushing is certainly not the procedure I’m familiar with, but sounds like it was effective in your case.

In my case, I simply purchased a new radiator. At 41 years old -not a bad inning for the old girl- it felt like the right thing to do for such a critical system. I doubt there’s a formula, but the cooling efficiency has certainly dropped a bit over the years. If I’m able to shave even 5 degrees off summer highway runs I’ll be feeling pretty good. Will update this thread once I’ve put some miles on it.

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1981 240D 4sp manual. Ivory White.

Most of the stuff I get to work on is neglected so I have learned to take the time to do it right, makes things easier in the long run as I'm often way the hell and gone where there's no traffic, no cell service and so on...

I was thinking about this as I drove my 240D last nihht near midnight ~ no AC the temp gauge was rock steady on 80* C .

I do wonder if you're worrying about nothing here as Diesel engines being compression ignition need heat and thrive on it .

EDIT : I spent five hours changing a fender yesterday, too bad I'm not allowed to post images .

As long as I had the fender off I replaced the broken hood hinge and dismantled the front bumper and cleaned out the accumulated leaf debris and polished it, treated the rubber impact strip and so on ~ I need to find another impact strip ere long .

The 'Might As Wells' take up a lot of time on 49 year old vehicles .

I *might* have mentioned previously how much I love this old base model worthless car =8-) .

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-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

If you bear in mind the key temperature differences I've noted -ambient and coolant- you'll see that my 240D would likely be uncomfortable doing what yours does regularly, desert heat with five adults in tow. 85F+ is not that hot of a day. Not sure people are reading that particular detail. Think this is why the vote seems split down the middle between "something is up" and "totally normal."

Your detail below (midnight at 80C) has never been an issue.
It's the 65mph+ on 85F days that give me grief.

In any event, new rad goes in this weekend. Fingers crossed.

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1981 240D 4sp manual. Ivory White.

I *do* under stand .

Not every engine runs the same temperature, that's just a basic and simple fact .

I hope the new radiator gets you where you want to be .

Remember to remove the collant temperature sender and gently clean the bulb that sits in the coolant .

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-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

Interesting, I haven't removed that before. You're referring to the sensor in the head between glow plugs?

Will that require draining the block as well, or will the rad be enough?


Edit: you know, on second thought... I'm inclined to leave well enough, alone.

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1981 240D 4sp manual. Ivory White.