Was performing an oil change for pap’s 2016 e350 and discovered the lower radiator hose. This is a rarely driven car with just under 30k miles on the odometer. It all started 3 weeks ago, before the oil change, the coolant light came on but no obvious signs of leakage on the garage floor either. I took it to a nearby gas station and they noticed the coolant reservoir at the low side. They filled it up completely and this drew my attention about the proper level. Is it suppose to be completely full? I searched on YouTube and saw there’s a plastic ridge inside the reservoir to determine the fill point, but for strange reasons mine didn’t have this. Any ideas? After filling the reservoir, the coolant light disappeared and everything was fine for about 3 weeks until I decided to change the oil and discovered the lower radiator hose like this. Any suggestions?

 

Hmmm. i would run the engine and let it get up to operating temps and check for leaks (carefully) with the engine running. It's hard to tell what you are pointing at. Are you suggesting the clip is out of place or are you pointing at the wetness on the hose?

Do you still have the M276 3.5L V6 in that car?

 

Hey Jetta, thx for chiming in. The lower hose has got wet spots.

 

If you overfilled the expansion tank, it will usually leak from the Temp sensor or thermostat housing first before coming out of the overflow tank cap, mine was overfilled and I had a similar leaks as your picture, once the coolant level was corrected in the tank, it stopped, so check this first, I have had no leaks since I remedied the mechanics overfill. Tank is full about half way, FYI

 

Pressure test your coolant system. Pressurize at the cap of the expansion tank, watch the pressure drop slowly (hopefully slowly) to verify you have an active leak, then look over everything to find out where the leak is coming from.

 

I’m thinking whether it’s the other way around where the lower radiator hose had been slowly leaking, hence setting off the low coolant level warning.

 

That’s a great idea!

 

Absolutely possible,

 

I assume you checked and it is water, not oil.
If it were the hose or it's O-ring then I can't imagine water traveling up like that, so imo it's coming from above that point. Since it's on the front side I'd say it looks like a classic water pump fail.
The standard weep hole placement is behind the pulley just below the shaft, between the seal and bearing:

 

I had a misfortune caused by MB Indonesia poor water quality used on the coolant mix, also the coolant mix I think is not 50%, but less.
It was still the oldie yellow coolant and not blue coolant, albeit car was made available in June 2014 to 1st owner and its mine by May 2018.

The leak could be from the steel end of the hose getting rusty and thus the o-ring won't sit well.

The main coolant reservoir



This is my equivalent coolant hose to yours, from radiator output to water pump input


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Even my water pump has minor leak from the seal.
Replaced it with new one.

A few hoses got rusty steel ends...duggghhh !!!!



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The worst one would be the hot hose, the one from engine output ( thermostat) to radiator input. 100C+ temperature chemically made the high TDS water used by MB Indonesia started to
carbonate / calcium up the steel end, aside from making it rusty.


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One word of caution. Do not remove the C clip ( catch spring ) , you only need to pull it up 1.5cm up when you need to remove the hose from water pump inlet.
Do not install the L end of the clip the wrong way, if ever by accident you completely remove the C clip.

To install the hose, the C clip (catch spring ) is to be in normal maximum-IN position, it will auto lock itself.

This is what I sent to my Indie techy, so it has Indonesian instruction


The #3 "soft hill" is the auto lock mechanism when inserting hose into water pump, no need to pull up the C spring ( catch spring ).

To confirm the soft-hill is locked well. below :


The C clip ( catch spring ) will lock into that "soft-hill"



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My indie tech made a mistake, he removed the C clip ( catch spring ) totally, when he re-installed he got it wrong. The L end should be oriented up ( in green cyan ) where there is a catch-protrusion to keep it locked well




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MB Indonesia actually made a mark in white, on the C clip and the water pump inlet





If M276.820 3.0 Turbo





On 3.0 Turbo it is more complex to remove the water pump input hose due to aftercooler in the way.
Its more of a by feel work, not by sight. So boroscope camera does help to see details.

 

Sorry about your misfortunes. About the rust and o-ring, I think so too. For peace of mind, I will replace the lower and upper hose, and change out the coolant while I’m at it. I appreciate you for taking the time to explain and post photos. Thank you my brotha.

 

How many hoses are there? I believe there’s a thin hose from the reservoir connected to the upper hose. Then the lower hose, so does 3 hoses sound about right?

 

For non turbo M276, 3 hoses yes. 2 big and 1 small I believe so.

 

Damn Prihada... Mine looked new inside, both inside the pump and hose. I have nasty water where I live too, so I use an RO filter, then run it through a DI.
I originally made the setup for washing my car, because I HATE to dry it, but it's pointless anyway because in the summer it would air dry far too quickly and the water spots are a nightmare to remove. So I have about 14gal of this RODI water stored in a tank at 80psi, and simply rinse the car off after my wash, and walk away. So worth it! Plus I drink and cook with it, and of course radiator and wiper fluid, or whatever else I need it for.
You probably get free car washes daily, but the RO is pretty cheap so if you don't have one. I can't even drink tap water anymore, since I'm accustomed to clean water. I accidentally cooked oatmeal with tap a couple years ago, it was nasty.

 

Yes, it was a VERY sad affair not about total $$ spent, but what calcium/carbonate built-up elsewhere I do not know of
I been using distilled water mix since then when I replaced the oldie yellow coolant with blue and been great.

Now it is using red coolant, blue no more sold by MB Indonesia.
I flushed real well during this blue to red coolant change and its where I replaced all hoses + plastics of 10 years old.