Trying to investigate where my coolant smell is coming from on the M278 in my GL550. I checked the plastic turbo cooling tubes near the ABS but things appear in order there. I did see some calcium streaks on the aluminum tube going to the turbo as if the hose with the crimp clam might be failing? Yet touching it things feel dry. Not sure if that’s evaporated. I will need to check it again after a short drive. The smell is present in the radiator area. Are these prone to leaks, plastic caps to fins and tubes perhaps? I can’t see well condenser and IC heat exchanges block it all. No drips or wetness. I looked in the engine valley what ever I was able to see. Things look ok there. Cant really tell if smell is stronger there or not. What’s the proper fill on the reservoir. Maybe it’s expanding too much and the cap is venting it maybe the cap is failing. IDK.

Let me know if you been through this with the truck. I can’t pin point it, but the smell drives me nuts.

 

Do you smell it on one side of the vehicle as compared with the other side? If yes it could be the reservoir cap needs replaced or the circulation pump is leaking to a greater or lesser degree.

The circulation pump on my M276 W166 emits a coolant-smelling vapor, but I have yet to see a drop of liquid leaking out. The small diameter hose connections from the reservoir to the circulation pump and down to the radiator bottom hose seem encrusted with dried coolant. Have a look there.

 

Not in the car unless the window is down. The caps seems suspect and I poked my head near the circulator pump you speak of. It’s definitely strong smell near the ABS block the pump seems to run even after turning off the car and you can hear the coolant slushing in the reservoir. No trace of coolant so far. Maybe vapors? Ugh

 

Generally the MB coolant leaves terrible residue where it leaks so it shouldn't be too hard to find. Any chance a piece of debris hit your coolers and caused a tiny leak in the front? Check through the grille opening carefully, it doesn't take much.

Pressure testing may help also.

You mention the turbo cooling lines, have they been replaced? If not, they are leaking, even if you don't see it. If you press on them they will snap off from being so brittle due to age/heat.

 

It sounds like the reservoir cap or circulation pump, as on many MB models of the era. Replacing the reservoir cap is cheap and easy. The circulation pump doesn’t seem like a big project but it is buried and has several hose connections, which might as well be replaced “while you’re in there.”