Hey guys experiencing a leak on my 06 ml500 maybe you can help. At first the auxiliary water pump was leaking I replaced it. Now I’m seeing dripping coming from where it looks like behind the engine idk because i cant see it. I just see thats its collecting on the driver side under-body splash shield. Any advice can would help. Thank you in advance...

 

What dripping do you see, eng. oil or coolant?

 

Its coolant

 

The only alternative you have is to remove the splash shield, run the eng. at operating temp. and find leak location. Of course putting the car on a lift is preferred.

 

If your heater is plumbed the same way in ML as R-Class, lines pass from aux pump through right-hand wheel arch and around between the 2 firewall layers.
(There is an outer layer quite close to the engine, with sound absorbing material bonded to it, then an air void, and behind this the firewall of the actual cabin structure).

I've had what sounds like the same leak, and it baffled me for quite some time where coolant was coming from. I could look down directly underneath the brake booster behind left wheel well
, and see a reflection from coolant pooled there.

Anyway, look under the rain tray and wiper motor linkage at the firewall.
If it's like mine there are two 13mm bolts at either end of a removable section of outer firewall, which begins left of the centerline of the car and goes around to behind the left strut tower.
Once the removable section of the outer firewall is out of the way things become clearer - underneath there are 2 plastic couplings/unions, for a pair of coolant lines.
With a small mirror you can look at the back of the outer firewall and perhaps see coolant trail. Or it may be on the engine-side of the firewall. Or both.
On a boat, these couplings would be through-hull fittings.

Between the 2 layers of firewall there are two, appr. 6" long hoses, which connect the plastic unions to their respective metal hard pipes to heater core.
So you have a total of 4 possible hose connections which may have started leaking, due to spring clamps at their limit of compression.
(There are actually 6, but the ones connecting to the metal heater core pipes don't get the vibration, so I don't think you'll ever actually see leaks there. I may be wrong though!)
The clamps are not adjustable and after the hose has aged and compressed enough, the clamp can do no more.

If accessing the hose clamp between the wiper linkage and the top of the remaining firewall is too awkward (distinct possibility), the thing to do is remove the wipers and rain tray.

I replaced the spring clamps on either side of the plastic union with worm screw hose clamps, and leak is gone.
I also replaced the plastic union, because it seemed deteriorated.
This piece slips onto the firewall into a notch and has grooved flanges to slide onto the sheet metal of the outer firewall.

Hope this helps

 

Im definitely goin to be looking into that today. Brung it here to my buddies shop so i can get it on a lift and get a better look at it. But this information you’ve given me super helpful. Glad to get advice from someone with a similar problem. Thanks again

 

Sure thing.

I had my car on ramps at one point, but couldn't see anything from underneath. Pulling the rear inner fender might expose a puddle, but not really the source.
If your buddy has a cooling system pump with fitting to match the coolant reservoir you're golden.
Since rubber is one of the materials that shrink when heated, often the small leaks will happen as the system cools off, but has been previously pressurized from running/heating up.
System ought to be topped off as best you can given the leak, without air trapped in high spots if possible.

Hooking up a radiator test pump to a cold system shows everything.

Anyway, any work I did to fix mine was done either standing beside left fender leaning over motor, or climbing up on the upper core support and reaching down to the back of engine compartment.
Good luck!

 

Can anyone provide the part number for the plastic union for a 2006 ML500 ?

 

This page is for ML500/4matic W164 N. America:
https://mbepc.net/1/fg/ml/63j/164175/0/83/181

Item 60 shows part number: A 251 506 00 18
, for Left hand drive (if I'm reading correctly).
If not, the number is A 251 506 01 18

Odd they show an R-Class prefix. The handedness would be because the way the bend would be the opposite way on a right-hand driver car.
Practically, the only actual difference would be that the rectangular plug which slips onto the edge of the sheet-metal would be on the opposite side.
Too bad you can't just twist that around the fitting.
(, or Can you?)