Leaking Headlamp Washer Jet – Cure

Over the past few months we had several bouts of severe frost and sustained bitter cold temperatures, the E Class Mercedes had stood outside unused for the majority of this time as I used the Vito for work.  As the weather improved slightly over Christmas we decided to go on a family shopping trip to Matlock.

I filled the washer bottle along with checking the oil and tyre pressures and off we set. Within 10 miles the ‘Low washer fluid’ warning lit on the dash and a little later the screen washers stopped functioning – empty!.  As it rained for the rest of the day, and the day after that, I was unable to look at the problem but suspected the washer bottle may have split due to freezing.

New Year’s day arrived, the weather in the morning although cold gave perfect opportunity to investigate. I filled the 5l  reservoir, marked its level with a pencil and waited….. sure enough the level began to drop but inspection proved the bottle to be sound and no water leakage was obvious – although it was disappearing at an alarming rate!  I removed the smaller concentrate bottle – the one that contains the undiluted ‘intensive wash additive’ as MB call it for the headlamp washer circuit.  Mistakenly this front fluid reserve is incorrectly understood by some owners to provide water to the headlamp washer circuit separate to the screen circuit, this is not the case – main water is drawn for the headlamp washer system from the main 5l reserve through a moulded mixing chamber in the bottle.  In this mixing chamber as water passes at high pressure, it draws a metered quantity of concentrated cleaner from the forward bottle (gravity feed), the cocktail is then propelled to the pop out headlamp jets.

After some torch shining and listening for dripping, the leak was located in the engine compartment on the driver’s side front below the headlamp assembly. I checked the pipe work and all seemed sound with no leaks and further squinting revealed that the water was in fact dripping from the body of the telescopic headlamp spray assembly. Where exactly was this leaking?  It was dripping from the rear of the main body of the jet assembly. Water was running backwards from the head, down the inclined jet and appearing beneath it at the rear, discharging into the engine bay lower tray.

You can see the rear of the jet assembly and the water supply hose indicated here by the red arrow.  The supply hose is easily removed from the assembly by presing the quick-connector inward (at the arrow tip on the photo) whilst pulling the pipe off the spigot.  At this point the remaining contents of the washer bottle will discharge from the pipe… watch your boots!

The next step is to remove the assembly completely for inspection, repair or replacement.

Disconnect Jet





Take a small, thin, flat blade screwdriver and carefully insert it behind the sprung cover flap and open it up – this will reveal the jet assembly that telescopes outward under water pressure when the wash is activated.  Normally this flap is automatically opened against spring pressure when the extending jet rod pushes it open when operated.




Removal from this point is fairly straight forward.  There is only a single cross head screw holding the assembly in situ.  Once the screw is out, this will then allow the withdrawal of the complete unit through the front of the vehicle via the held open flap.  Once removed and the unit emptied of water, you will be able to pull out the piston to its full extent whilst grasping the main body, then cover the supply spigot with your thumb and allow it to spring back under its own pressure – once it has, it will internally pressurise the unit allowing it to be submerged in a bowl of clean water and look for leaks in the form of air bubbles.   On my unit the leak was at the end of the extending portion (Green arrow B on the photograph).   The part where the extending rod joins with the twin-head jet.  On the final photograph the jet assembly can be seen pulled and extended whilst in place on the car. (Grasped and pulled in the direction of white arrow C)  Obviously removal of the following component parts is best done with the whole jet assembly removed from the car, although I suppose it would not be impossible to do whilst it is still installed.  The jet head can then be carefully removed by holding up the small plastic tang that forms the locking arm of a ratchet – this can be seen arrowed and numbered as A in the following pic.  Once the plastic ratchet arm is held up with a small jewellers screwdriver, the jet head can be pulled out of the end of the extending rod.  Once removed, the rod will no doubt spring back into the body! – don’t worry about this, it can still be reassembled with ease.


Jet fixing screw


Once the spray head is removed it can be seen to be sealed to the body with a small purple rubber O-ring. It was this that had an accumulated build up of muck and grime preventing a perfect seal with the inner barrel of the extending main body obviously allowing water to pass by. Once cleaned, re-seated and bedded in the smallest bead of silicone sealer (I did not have a replacement O-ring of the correct size) The jet head was then pushed home into the main body, inserted to butt hard up against its plasic grey ‘end skid’ clip that prevents further travel inward into the end of the telescopic cylinder. Once attatched the complete unit can be tested then refitted into the bumper in the same manner it was removed.

Tested as a complete success, this simple fix was worthy of posting – Have fun !

Washer Jet

18 thoughts on “Leaking Headlamp Washer Jet – Cure

  1. Hi this helped a lot but I found my unit came out the back, but alas it did not stop my leak it must be something in side the unit but thanks a lot

      1. On my 320 the headlight washers just leak from the jets after first use, as the water just syphons out is there a knackered anti syphon valve missing somewhere?

      2. Hi Gary, I think you will find the shut off is actually a function of the telescoping jet assembly, its worth a look at the post on repairing this it could cure your problem.
        All the best Steve

  2. Thanks for posting this ,followed your guide, but all my o rings were sound but when extending the telescoping part and sealing off the feed, it wouldnt pressurise,
    On removing jet assembly again I found a small plastic moulding that appeared to have dislodged from a spring carrier, guess this is the anti syphoning valve,cleaned it up added a drop of cyanacrylate popped it back in, now all working fine,
    Take care when dissassembling the Jet assembly as the part in question is only as big as a small cap from a biro and easily missed . Incidentally, mine was on a CLS320 but parts appear to be Identical.

    Kind regards FRED

    1. Thanks Fred,
      Very helpful tip of further dismantling of the washer jet, glad you got it fixed. Once you understand how they are supposed to work and of course how they are assembled, a successful repair is indeed possible.
      Thanks again
      All the best

      1. Have you opened the jet assembly? If yes can you give me an idea on how to do it because I cannot figure it out.My leak is coming from the base of the telescopic arm,seems like there is a rubber o ring which might not seating properly inside the main body.By the way mine is Porsche Cayenne but the setup is similar,thanks

      2. Hi David,
        From what I remember the only removable part is the jet assembly at the front. The rear telescopic section is I think assembled all from the back and the end cap either glued or ultrasonically welded. I think you may be at a point where you can progress no further! However do just be absolutely sure it isn’t the front section that I have outlined, leaking and running back, as often the mounting angle can give a false impression in the way in which the water finds its own level and a place to eventually drip from.
        Good luck.
        All the best

  3. Hi Steve,
    Thanks for your advice,in fact you might be right,the water comes dripping out mostly when the body is inclined,and this happens even when wiper/ washer is not being used (car parked).
    My understanding is that the entire system is pressurized all the time even when engine not running.I need to remove the part again and have a closer inspection.
    What baffles me is that everything seems to be in place,even the 0 ring attached to the spray head seems to be in good condition.Could it be that the spray head is not butting hard against the ‘end skid’?

    1. Hi David,
      The system is not pressurised when not in use, in fact it is the high pressure to the headlamp washers that causes the piston jets to extend pushing back the trim flap before spraying. The headlamp washer pump is a very powerful one as you can probably see by the diameter of the delivery hose to the jet assembly. I think the O ring on the jet ‘end’ gets some stick as it is obviously stressed overtime as the skid continually travels over the opening flap, it is this that makes me think this is probably the area you should be looking. When the jet is all dried off just apply the slightest smear of silicone sealer around the end O ring before reassembly. If this was the source of the leak then it should now be suitably sealed.

      On some models with a similar jet assembly system, if you trace back the pipework you may find a small black tubular inline non return valve. It isn’t really a non return valve as such, more of a non-leak down valve. It contains a small spring and a diaphragm or ball-bearing that is sprung loaded into a seat. Under normal standing pressure the ball is pushed into its seat and no water is allowed to pass by gravity. Once the pump is activated the pressure overrides the ball/spring, lifting it from the seat allowing water to pass. Once the wash cycle is over and pressure in the line drops then the ball closes again cutting off further supply. These sometimes get crap in them preventing the ball from sealing completely against its seat and allowing water to pass under gravity – crying car! These things are glued together and have to be thrown away and a new one fitted but if you can find one on your system it is another possible cause. – Or as an alternative fix, consider fitting one inline to that jet, that way only a smaller quantity of water could possibly leak away as you have effectively cut off the static feed! (Have a look at the valve/911 part that was used on these vehicles fitted with that option circa late 80s, I am sure it will fit.)

      All the best

  4. Hi Steve,
    Good day,many thanks for your valid information.I did pull it off the car one more time to have a closer look.The purple 0 ring at the end of the spray head is fine,I even swapped it for a new one but unfortunately my leak is not coming from there.When I immersed the whole part in a bucket of water the bubbles are coming out from between the body and the telescopic arm.
    As you mentioned this part cannot be taken apart ( without breaking it) because its ultra -sonically welded.Since I had nothing to lose and out of curiosity I made a clean cut towards the bottom end just above the inlet.When you make the cut make sure you don’t cut through!If you do you will damage or possibly even cut through the plastic piston inside.Hence cut along the circumference until the blade goes through. Inside there is a very long metal spring,and a plastic piston with another 0 ring attached at the other end.Be careful when you are cutting the main body as the spring is under compression and it can injure you once the body is cut apart.
    Once I looked inside the chamber I could see two deep scratch marks along the entire length of the wall probably caused by some debris I found attached to the piston head.The seal looked and felt perfect hence my suspicion is that the scratch marks were deep enough to allow water to bypass the 0 ring.
    I did a clean up,used fine sandpaper to get rid of the scratch marks lubricated the 0 ring and finally reassembled it holding it all in place with the use of a clamp whilst using my soldering iron I made a plastic weld.I reinforced the weld by applying a patch of plastic gauze,covered in appoxy glue.
    After allowing the glue to dry and cure (24hrs) I tested it and it worked perfectly!This process was very time consuming however it was worth the try.Hope this helps others with the same issue.


    1. Hi David,
      Thats what I like – a born tinkerer! It is kind of rewarding to repair something like that, even though it probably would not be economical from a commercial point of view – Your own car and own time have no value in real terms. Super result.
      If you ever fancy a job writing an article or two on your future adventures, just take a few photos as you go, and send them to me and I will post them up for all to benefit. My own personal enjoyment of repairing (or sometimes attempting to repair!) the unrepairable is that before hand you think the job to death, almost working out a scenario that explains the failure – then needing to take it apart to see if you were right!

      Years ago I went for an interview and I sat across the desk to a guy who was obviously ‘one of us’ – The discussions about the job and fault finding techniques lead him to say ‘I bet you used to take things apart at home as a kid, the TV or whatever’ sure enough he knew I had, because in his childhood he had done exactly the same.

      PS. I bet the plastic fuming under the soldering iron (holding breath) really made your eyes sting!

      All the best

      1. Hi Steve,
        Good day,many thanks for your comments.As you said from the commercial point of view it doesn’t probably make sense to go to this length to repair such a part,because it’s time consuming and there is no guarantee of success.
        Your last line in your second paragraph is a perfect description of who I am.I usually don’t take “not possible” or ” can’t ” fix as an answer.I see it as a challenge and this in turn gives me the drive to “fix” things.I feel society in general has accepted the notion that a part has to be replaced instead of repaired.Many times that statement is true (for commercial reasons that we already mentioned)however if you have time,tools and knowledge there is nothing stopping you from trying “attempting to repair “.Its a mixed bag of results,at times successful at times you destroy that part,but anyway if its destined for the bin what’s there to lose?Its a learning curve,but the gratification you get to prove it can be fixed is amazing!
        Ooh gosh yes those fumes sting your eyes same way like when chopping onions,but a small fan blowing from behind me made it more bearable whilst holding my breath!
        I’ll be more than willing to share my “adventures ” with your fellow Mercedes owners whilst I work on my Porsche….hehehe.


  5. Many thanks for this. I have a Mercedes E430. After winter I found leaks dripping from the centre of the car. Expecting to find a burst pipe I removed the plastic tray from under the front, and found both headlamp washers were leaking, the water from which was coming from the centre. After using your column’s advice to remove one, I followed your full instructions and fixed it.

    Then, instead of removing the second one, I just removed the head part and cleaned and siliconed the purple O ring. Clicked it back in and voila! So much easier the second time. And no leaks.


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