im lousing coolent MERCEDES-BENZ

that hose is the drain line for the injector valley. it runs from the back of the valve cover down the firewall side. usually it leaks diesel when you have the black death injector seal failure but if it is coolant then your injector valley is full of antifreeze. pop the black plastic engine cover off and take a look.

yeah sounds like the injector valley drain. i had this happen on my 04 sprinter with 280k miles. i saw a puddle of gold coolant under the van right near the transmission bell housing and traced it to that little rubber hose. i freaked out thinking i had a cracked block or head gasket failure.
turns out it was actually the thermostat housing gasket that had failed at the front of the engine. the coolant was spraying out under pressure but only a fine mist. because of the fan and airflow it was getting blown backwards under the black plastic cover and pooling up in the injector valley. once the valley filled up it just overflowed down that drain tube at the back. i thought for sure i needed a new head.
i replaced the thermostat with a Behr unit and put in a new gasket. cleaned out the valley with some rags and brake cleaner. filled it back up with Zerex G05 and pressure tested it. dry as a bone. check the simple stuff first before you assume the head is cracked. also check the little hose that goes to the egr valve sometimes that one leaks and sprays into the valley too.

@CharlesV is right that is the drain for the black hole of death area. if you have antifreeze coming out of it you have a pool of coolant on top of your cylinder head. could be simple like a hose spraying but could also be a cracked head.

@secret_m don't scare the guy yet. my 2006 leaked there and it was just the heater hose rubbing through where it crosses over the top of the engine. it dripped right down into the well.

@owen_m just saying he needs to pull the cover. if it is the head cracking it usually happens around injector 1 or 2 but the fluid flows back.

@secret_m @owen_m definitely pull the cover. you need a 5mm allen key i think. remove the three bolts and lift it off. if it is full of green or yellow liquid you found the source. hope for a hose leak.

what color is the coolant. if it is green someone put the wrong stuff in. these t1n vans need the gold zerex g05 or the mercedes spec stuff.

@Harry.B probably not the time to lecture on coolant type if his head is cracked lol. but yes correct spec is important.

i have the same issue right now on my 3500. just noticed the drip yesterday. going to pull the cover this weekend. hoping it is just the water pump spraying back like Charles said.

I have dealt with this exact symptom on a customer's fleet van last month. 2005 freightliner with the om647 engine. It had coolant dripping from that specific drain hose above the transmission.
We pulled the injector cover and the valley was swimming in coolant. We pressure tested the system with a Stant tester pumped up to 16psi. It turned out to be a hairline crack in the cylinder head casting right next to the number 3 injector well. It was only opening up when the engine got hot at first but eventually got bad enough to leak cold.
We ended up having to replace the cylinder head. It was a big job. While we were in there we did new Bosch injectors and a new water pump and thermostat. The total bill was painful. I really hope yours is just a hose or the thermostat housing spraying back. The way the valley is shaped any fluid that gets in there has nowhere to go except that drain tube at the back. Clean it out thoroughly and dry it then run the engine and watch with a flashlight to see exactly where it starts welling up.

@Oliver Jones that is my nightmare. how many miles were on that van.

@C. Smith it had about 340k on it. hard city miles though.

check the heater control valve too. it sits on the firewall but if the hoses are routed poorly or leaking they can drip forward into the valley area depending on how the van is parked.

@george.evans heater valve usually drips down the side of the battery tray area not into the center valley. my money is on the thermostat housing or the egr coolant hose.

also check the auxiliary water pump. on my 2006 it is mounted on the firewall near the brake booster. if that leaks it drips down the back but usually misses the valley drain. that drain is specifically for the injector area.

i had a leak from the egr cooler hose that filled my valley. it is that short little elbow hose that connects to the intake manifold. it developed a pinhole and sprayed directly under the cover. replaced it with a generic hose from napa and it burst again in a week. buy the molded mercedes hose or the gates one that is shaped correctly. that bend is tight and straight hose kinks.

@aVa.Daies... good point on the molded hose. the generic stuff never lasts on these engines with the heat and vibration.

@user_437353 good luck let us know what you find. bring a turkey baster to suck the coolant out of the valley so you can see the leak source.