When I use the wiper, the fluid does not come immediately. It comes only after the wiper goes up. I want to avoid the dry run. Where could the fault be?

 

It's normal. It takes a second or two for the fluid to get pushed from the pump to the nozzles.

IMO, you don't want fluid sitting in the nozzles where they get clogged.

 

It seems like a really strange behaviour to me. I live in a rural area and in the warm months we have a lot of bugs on the road that get splattered all over the windshield. When I trigger a wipe cycle it first smears the bug juice and road grime all over the glass and then it sprays it with wiper fluid in a feeble attempt at cleaning up the mess it just made.

I got the car used after it came off a lease, so I don't know what the default behavior is on a brand new W212 but this is the first car I have owned that did this, and it seems wrong.

The spray nozzles are heated on my model so they don't freeze in the winter, so to me it seems like by design they should have liquid in them always ready to go. Why else put the heating element in them?

I'm now starting to think that there might be a problem with the weeping hole that all car windshield washer pumps have, that is designed to release extra pressure when the pump is operating. Perhaps it is leaking when not in operation, and the fluid lines slowly leak out?

I might try putting in a new pump. How accessable is the washer reservoir?

 

All the Mercedes I’ve ever owned behaved like this.

 

correct, this is not an issue. all MB's are like this

 

After getting feedback from all over that this is normal, I did some testing myself and found what the problem was. It was getting so bad that the spray wouldn't come through until the wipers almost did a full cycle and returned back back to the starting position! Instead of replacing the pump I decided to flush out the system using pure distilled water. It took emptying 2 full wiper tanks filled to the brim with distilled water and a bit of rubbing alcohol mixed in to completely flush out the gunk that the Rain X fluid left. Now, when I call for the wiper, they start to go up, and are IMMEDIATELY followed by a VERY STRONG fine mist of water. Problem fixed. It was Rain X wiper fluid that caused the problem and bogged down the pump and the nozzles, and left a nasty yellow film all over the inside of the wiper fluid tank. Never using Rain X again!!!

Long story short: Rain X washer fluid caused the problem, don't use Rain X !!

 

 

RainX fluid is a known issue and has been mentioned many times on this site. Glad you found the problem

 

Negative, my 06 SLK280 is NOT like this.

 

mine has been gradually getting slower and slower, now I know why. I never liked rainx wipers or repellent now will stop using fluid as well.

 

I mix a tiny amount of simple green in my other car's reservoir. It seems to do the trick when there is tremendous amount of bugs committing suicides on my windshield. I thinking of doing the same thing on my E class. Any thoughts?

 

For me it is distilled water and a squirt of dawn dish soap. Have been doing this for 20 years now. I got tired of the gunked up crud on the washer nozzles from hard water and 'coatings' for the windshield. Simple Green would be fine as well I would think except it is not great for aluminum long term, should there be any in the path of the fluid or below the windshield.

 

I'm going to try the distilled water and dish soap in mine. What do you do in winter? It gets down to - 30 Celsius where I live.

 

Just use the cheap blue stuff. Never an issue with any of my cars over decades of driving. Including Mercedes. I have to use a fluid with freeze protection so no water and dish soap for me.

 

I refilled my washer reservoir to the brim the other day. I noticed that when summoning the washer, the spray WAS immediate, as the wipers started to work. But after that first wash (less than full), it's back to the normal spray delay.