ColonelKlink

Hi all,
MB 2014 E550 Sedan 4matic M278.922 USA
155k+ miles, many owners , 80%+ MB Dealer Service history :-)
New to me vehicle. MB new to family. I have two 'jacks' and attempt basic maintenance on other family vehicles.
I looked extensively in W212 forum and found basic info that helped eliminate certain causes, but I am still looking for solutions to the below. I hope I am posting in the proper place for tech advice. (Mod, please move if nec)....

A) Where can I locate 'exploding diagrams' of engine compartment including everything forward of firewall? I want to match part on car within diagrams. These diagrams would help me narrow down possible sources and parts to solve below.

B) What is this oil hose? (I hope I can attach photo) I have an engine Oil Leak (as opposed to other fluids-transmission?) coming from under the main front radiator, possibly from the oil cooler (?) there are two metal tubes facing to the rear. Both are located on the driver 'half' of the center line. The tube closer to the passenger is leaking (what I think is) engine oil. Leaking tube has two nuts on it that connect to rubber-type hose going toward the rear. Turning the nut easily with a crescent wrench, does not tighten the connection, but also twists the hose - so I cant do that. Clean tube has only one nut- seems snug. Symptoms: No warning signs. 'Check oil at next gas stop' just appeared on dashboard after 900 miles of driving (though I wrote most of this note before the warning). Manual check shows oil is proper level and clean, though I do not know what viscosity. Records show different owners have changed the engine oil and filter three times in 15 months and 15k miles. The light oil mess in the undercarriage goes back to the first Cat Conv, then continues light layer down the driver side underbody. Certain levels of grim indicate to me that this leak has been going on for awhile. What is this hose? Is the one/two nut disparity correct? Where does this hose connect to? Is this engine or transmission oil? Right now -everything is black and grimy, what little 'half-clean' drops I can gather seems to have a yellow background not red. How difficult is this hose to replace DIY? Also, I removed both hard plastic under-engine pans to visually locate this oil leak. (My $10 OBD tool showed no DTCs and all passing grades after 750 miles of driving. I do not have a better scanner yet)

C) Coolant Leak. Where to look? Will coolant dye (from autoparts store) damage coolant, engine, etc? Symptoms: Low coolant alert comes on drivers display, Blue, clear, no dirt or discoloration. Coolant will lower from Black/white level to one inch below after about 2 hours of driving. Distance does not seem to matter. On initial 400 mile highway drive (without knowing coolant issue), engine ran for about 9 hours in 40F dry weather with high heat, low blower venting thru sunroof resulting in discovery (next day) of coolant about two inches below mark. Topping w/ official MB coolant, took 90 minute highway drive (below speed limit) on 65F day, A/C set to 75F, low blower, vent thru sunroof. Came to level driveway, idled for about 10 minutes. Two hours later discovered puddle (full pint+) of coolant that had leaked from about the center of car, front of door location (we did not expect this, thus did not measure exact location). There were no puddles before or since. The Coolant reservoir was replaced by previous owner in the past year with a Mahle unit. The Mahle cap does not click like the other coolant OEM mini-reservoir cap does in the middle of the engine under the cowling. There is a very small amount of dried out coolant on the hoses around the main (Mahle) coolant reservoir near the top. Nowhere else. I ziptied four paper towels around the reservoir - cap, three hoses - no wetness or discoloration of any kind. So, I do not know if the dried-out coolant is recent or old (before coolant reservoir was replaced). There is no evidence of coolant leak from below with protective pans removed. Water pump replaced 10k miles ago. Spark Plugs replaced 20k miles ago.


What is this leaky hose? Looking up from floor toward hood, front of car, far upper right is single radiator fan. Both hoses at bottom of radiator, behind bumper on driver side. Leaky hose is 'passenger side' hose. (Front protective pan must be removed to see this area.)

Over time I will update.
Your answers to my questions above and suggestions are much appreciated.