What is causing my windscreen to smear?

TNGL

TNGL

TNGL

Soldato
Joined
2 Jul 2010
Posts
3,098
I've been having a few problems with smearing and after cleaning the windscreen and the wipers today, I went for a drive and it started to rain.

Whilst at low speeds, it didn't smear and the rain wiped away quite well. I was ecstatic. This was until I went down a dual carriageway (still, whilst it was raining) and noticed all of the marks I had previously removed were now present and I could hardly see where I was going.

Now, if I active the windscreen washer jets it will initially clear these smears and everything will be fine for a few minutes until the smears gradually start to come back and repeat. I have noticed that when the rain lands on the windscreen, it sticks and doesn't roll anywhere (if that makes sense) - it almost looks as though the raindrops are of a light whiteish colour on the screen, as if they were diluting something on there.

I topped the washer fluid up not too long ago, so I don't think it could be that. The windscreen and wipers were initially cleaned at a hand car wash, I have also tried to clean the windscreen and wipers with standard glass cleaner but the smears continue to appear.

As a general observation, when I wipe the smears with my finger, black gunk comes off.

I am thinking of:
  • Cleaning the windscreen with a clay bar in case this is just the result of lots of dirt/oil that's accumulated which isn't really visible to the naked eye and cleaning the blades again
  • Replacing the washer fluid again and then cleaning the screen/blades again too
  • New windscreen wipers (though why would they clean the screen properly when activating the washer jets - perhaps the blades are in fact worn and the washer fluid provides the extra lubrication they need to function?)
Smearing occurs on both sides, all across the windscreen.

Any ideas as to what might be causing this? Looking to narrow it down rather than doing all of the above or if the cause is much simpler and easy to solve.

tldr; smears on both sides, when activating washer jets it gets rid of the smears for a while but they come back after a few minutes, seems to occur mainly when driving at speed, when wiping the smears with my finger black gunk comes off.
 
Sounds like contamination on the screen, or cheap blades breaking down and causing contamination.

If you already have a clay bar or cloth I'd give it a good scrub with one of those first. Or a proper abrasive glass polish, rather than one of those spray on-wipe off quick cleaners.
 
Hasn't had rain x applied to the window has it? I had to replace my last wipers after a dealership applied it to mine and it caused no end of smearing issues.
 
the last time i used rain-X i never used the wipers - soon as you were at a decent speed the drops just slithered off the glass. many years ago though, maybe they've changed their formula?
 
I no longer use RainX because of the smearing issue.

But I've seen the same effect regularly, caused by valeters haphazardly spraying that greasy silicon shiny stuff around an engine bay and getting it all over the wipers and bottom of the screen.
 
Clay your windscreen then give it a good clean with isopropyl alcohol and paper towel. Go over the wipers thoroughly with the IPA. Maybe replace the screenwash too, and make sure it's not too concentrated. Then see how you go from there.
it's probably just some cleaning product that's taking time to rub off. If the water is sticking, then it shouldn't be RainX; that can cause smearing sometimes, but it would help water roll off anyway.
 
The reason washer fluid is different to rain/spray is that spray is usually full of grime and greases from the road and windscreen wash has an alcohol solvent in it.

Fine scratches on the windscreen, fine nicks in the windscreen and/or wipers etc trap small amounts of air and that interacts with the grime and causes smearing. The whiteness is down to the emulsification of the road grime and water.

Other things that can aggravate this are silicone from car wash waxes (as they wear), rain-x (as already stated) and other chemicals used for cleaning (which should not be used on glass).
 
Thanks for the suggestions - haven't had much time this week so my plan of action for tomorrow is:
1) Clay the windscreen
2) Clean it with IPA if I can get my hands on it (if not, I've read vinegar is also good)
3) Fit new blades
4) Flush and replace windscreen fluid

Probably won't be able to test if it's all worked until the week after because as sod's law has it, we are expecting no rain in my area this weekend.

I would be more pragmatic about it which was the initial goal but I just want to get it out of the way and sorted now.
 
Clean the windscreen as best as you are able beforehand and use fresh clay if you are able. I'm sure when I clayed the windscreen on my previous car I caused some scratches.
 
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