White residue - looks like it's coolant related
 

Running a diesel purge at open throttle seems to have surfaced a few issues. First the injector return hoses burst open and had to be replaced. Now I have found this residue in the engine bay (valve cover and pictured hose mainly).

The radiator took a liter of distilled water before it filled to the top of the filler on a warm engine - it had zero oil residue floating on the surface. The engine oil on the dipstick also looked normal. No oil leaks anywhere and zero oil consumption.

The car has its original Behr radiator and severely rusted oil cooler. I plan to have the radiator re-cored. I suspect the pictured hose may be leaking. Diagnosis/ thoughts are welcome. Thanks!

I'd do a Citric Acid flush before letting anyone touch that radiator, few can re assemble them sans leaks these days and that one isn't very rusty .

Remember to have the HEATER ON and drive it a while once the cleaning mix is in ~ you're not just cleaning the radiator, you're cleaning the entire water jacket that's coated with the rust silt .

This might be coolant additive residue (evaporation or rather small droplets flung around by the fan at high revs. Looks there is some on the fan shroud too).
Check for leaks (after pressure build-up, when the engine has reached oper.temperature-the upper hose should be firm to touch) on the radiator and the weep hole of the water pump (engine shut, of course).
Also this could have happened if some coolant(or just vapors) escaped via the overflow tube(on the filler neck of the radiator itself).
I'd also change the rad cap if it's the original one (get a Behr/OEM with the same pressure setting).
When was the last time you had checked the coolant level before the purge operation? It might be just a coincidence.

The radiator was full at cold temperature when I purchased the vehicle 700 miles ago. It's lost 750ml of coolant since then.

At peak operating temperature, the hose (in the 2nd picture) was bubbling with a mild leak where the translucent hose meets the nut. It is likely the fan blew the fluid onto the valve cover as it travelled upwards. What hose is this? Is a leak common?

Were I to re-core, I would do it at Aaron's radiator. They specialist in metal classic car radiators and have a pretty decent reputation here in the UK. They even have another diesel rad in their workshop currently.

Haven't heard of a Citric acid flush done of a W114/5 but am open to try. Anyone documented how to do one on a /8?

Do a coolant system pressure test before you start replacing parts. No need for a fancy-smancy one as the /8's use a plain generic cap. 1 bar/15PSI.


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No need to spend a ton of money. You can usually get a loaner from auto parts stores.

Thanks for the advice. I'd like to know what's causing this first, so a pressure test may be prudent, followed by a flush. I've filled battery water for now.

A couple pictures that point to the issue and may offer clues. Can anyone share what the translucent hose is called? I suspect the leak is emanating from there the pictured joint

Translucent hose is the vacuum pump exhaust air hose.
It is just a vent for air from the vacuum pump that goes to your air filter.

The dried coolant on the translucent vacuum pump vent hose, radiator hoses,and radiator is most probably from leakage of coolant from the top radiator hose when the system is pressurized.

The MB rubber hoses remain quite pliable for an amazingly long time.
The top radiator hose may be long enough to allow you to trim an inch off the hardened hose end, reattach the trimmed hose to the top radiator nipple, and get a better seal.

My year and model has a different arrangement of hoses. But, when the Hoses were removed the Aluminum casting where the hoses seated had deep pits of corrosion on them.
The pits were causing a seeping leak on one of the hoses.

Not an issue with the citric acid flush in of itself; but in the past some have found that the rust or what ever residue was in the cooling system had actually been plugging up some small holes. And as a result of that people have found their Heater Core leaked, a Core/Freeze Plug leaked or the Radiator leaked.

Although this is problem that happened back when people only put Water in their cooling system. Often when people did a coolant flush it loosened the rust in side of the Engine Block and that rust would keep coming off for Months and Months and Months plugging up the Radiator and causing overheating.

I have owned a car since 1968 and the plugged radiator after a flush has happened to me and also to my Father on one of his Cars.

Citric Acid Cleaning & Flushing
 

That's why it's so important to DRIVE it for a while ~ if the radiator's tubes clog after flushing it means you didn't do the job fully not anything else .

Yes, I had a welch (? SP ?) plug begin to weep after flushing my very fist 300CD, the entire cooling system was ruined because the damnfool I bought it from had filled it with tap water after bypassing the failed & leaking evil Klima I servo from hell .

If it begins leaking because you flushed it, it was bad and waiting to do you dirt .

My w124 was showing a similar spray pattern as the first pic in your original post. Radiator had a pinhole leak on the driver's side, down low. The cooling fan was picking up the leaked coolant and blowing it all around. The inside of the fan shroud was covered in that same chalky white mist. New radiator cured the problem. YMMV

I agree with the part in red. But, what has happed to at least 2 others in the past they thought that their job was going to be done over the weekend. If you happened to look at past threads where I posted the warning I recommended planning some backup transportation to work if their Mercedes was there only Car.

For myself If my Coolant System is working properly why would I do a flush and risk the chance of precipitating other issues.

I mean if our heater core starts leaking you have a serious job ahead of you.

Since those early days I have only used flushed if I was using some sort of block sealant and then I just used something mild like the Auto Parts store sells.

Anyway that is how deal with it personally.

In the case of the original poster he is in the UK where it is a good deal cooler. I live in Southern CA where today it was 91 degrees F. If I am not overheating in this weather why would I bother with a coolant flush even if there was some residue in my coolant system?

Valid point. Even with what appears to be a very small leak somewhere and our relatively mild summer temperatures, I have hovered around 180-190 degrees and never exceeded this. I appear to have a couple options:

1) Leave things alone and top up with coolant occasionally. Enjoy the benefits of living in a temperate climate for 90% of the year.
2) Perform a citric acid flush prior to the radiator re-core (new radiators are NLA)
3) Re-core the radiator and call it a day

Ignore a problem at your peril .

I too live in So. Cal., it was 109* F in Pasadena before noon to day, at noon 0:clock it was 99* F just South of down town L.A. .

I like to drive in the Desert and never need worry about by cooling system .

I was able to take 3 videos further highlighting these symptoms:

1) This is BEFORE the car is started. Hasn't been driven for 5 days so the radiator is dry.

2) This is AFTER a 70 mile road trip. Car maintained its temperature but you can see the leak. Could be the upper hose as ALEC shared as the coolant does appear to be concentrated in that area.

3) Wetness on the venting hose.

Before a citric acid flush, and radiator replacement (which still may be needed), I would recommend ruling out a leaking top radiator hose.


Clean up the area and the mating surfaces very well:

Warm soapy water and a stiff nylon bristle scrub brush can dissolve and remove most of the crusted coolant residue on the radiator.

The hose clamp may need a soak with penetrant as it looks rusty.
It should be eventually replaced with a Norma style clamp.

The hose may be difficult to remove.
Gripping the hose with sliding jaw pliers and giving it a twist can break the adhesion between the hose and the nipple.

Warm soapy water and a terrycloth rag will remove any internal hose residue.
You need to clean about three inches into the hose, just a bit past the bulge in the hose end (due to the flared part of the nipple).
The hose end may need to be trimmed if it is too hard or has a hidden split.

NEVR DULL wadding polish will clean the hose nipple quite well, without damaging the surface.
Avoid the temptation to use sandpaper or a Scotchbrite pad.
Fine steel wool would probably be okay.


Once everything is cleaned, reassemble and test for leaks.
Hopefully this will cure the leak.
If not, at least it will be easier to track down the leak with clean surfaces.