Stubborn Adhesive
 

The Xpel headlight film that came with my CDI became discolored to I removed it. Film came off fine in one piece. But there's some adhesive residue that is proving to be particularly difficult to remove. Xpel says to use thumb and maybe some alcohol or other adhesive remover, but that's not working.

Any thoughts as to what method and/or solvent to use?

Give ammonia a try.

WD 40? High detergent soap such as Ivory liquid? Neither of those are solvents but as a sticky material is moved around both those products will keep it from sticking again.

Sometimes the simplest things turn out to be good solutions to removing sticky stuff. My final go to for a solvent is acetone. It's not something that should be used without a trial area that you're ready to sacrifice for the cause.

Lighter fluid works well on removing adhesives from plastics.

PB Blaster is also effective as an alternative. Something most people have laying around too.

Give GooBGone a try, but test it out on a small area to see make sure it does not make things worse. Good Luck!!!

Are you using 91% or more alcohol?
 

The rest of that stuff is water. Useless on the headlights. I would go ahead and try the 91%, or 99% isopropanol if you can find it local. It will strip paint! But your headlights should have a polycarbonate cover. Isopropanol should clean it.
Unfortunately, some "fixes" written by manufacturers do not include the years of exposure to weather, heat/cooling cycles and a myriad of chemicals. Perhaps you may end up buffing the area with some auto lamp buffing compound.


snapped_bolt

Goo Gone is the best I've found for removing residual adhesive. Also, it won't harm the plastic as many harsher chemicals will, including anything with alcohol. I've used it to remove a myriad of unknown sticky substances from equipment previously installed in retail locations. For really difficult areas, saturate a piece of paper towel and place it on the surface to prolong contact time.

Larger quantities of Goo Gone are available at Lowe's and Home Depot.

If I'm not mistaken, that's a water based adhesive. If the lens is glass, try hot water and a brillo pad.

I may get flamed for this (literally :P) but I've been using small amounts of unleaded gasoline on a paper towel to wipe off glue residue. It works so well I rarely use isopropanol anymore. I have a tiny bottle I collect from draining the float bowl on my dirtbike after I ride it.

If you do this use a tiny amount that you could manage if it goes up in flames. Lighter fluid is naphtha which is similar to unleaded gas. Keep a fire extinguisher handy. No open sparks or flames.

Transmission fluid.

Sixto
98 E320s sedan and wagon

IF (God Forbid) the Mirror Finish of the Lens is Harmed...
 

Rust Oleum's
"Wipe New"
WILL RESTORE them to Crystal Clarity.

'Did an old set of VW Golf Lights on Friday (They Were Yellow with UV Damage)
And they looked "Factory Fresh" in about 45 Minutes.

BUT YOU MUST FOLLOW ALL THE DIRECTIONS !
[As in a Beautiful Paint Job,Prep work is 80 %]

3M makes a specialty adhesive remover.
But have you tried Goof Off. (NOT OOPS.. too powerful)
Turpentine.

The lenses on the W210, and many modern cars, are polycarbonate. Similar to Lexan. Need to be very careful as to what solvents or chemicals are used for cleaning. In particular, avoid strong alkalis like oven cleaner as well as even isopropanol. If you use these, it could result in crazing of the lenses. Expensive to replace!

Do a search for cleaning Lexan and polycarbonate. It should hopefully tell you what not to use, but ignore the posts in forums - they tend to suggest products that ignore the effect they will have on the Polycarbonate/Lexan. This is from one hit:

In absence of any better information, I would start with mildest products like say, Windex or soapy water and a coarse rag and try and get the adhesive to ball up. If a remover seems to be needed, try a citrus based one like Goo Gone (3M has one too). Again, put some on a rag; rub until adhesive balls up. Maybe finish with Windex and soap and water to remove any traces of remover. I have had some luck on flat plastic surfaces using a sharpened plastic paint scraper after first softening the adhesive. Metal ones work better, but will damage lens.

Finally, using your thumb as Xpel suggests "may" work better if you lightly warm up the surface with a hairdryer or maybe even just leave car in direct sunlight.

Remember the secret to adhesive removal is you have to break the bond between the adhesive and substrate.
Then you have to keep the adhesive dissolved in the solvent, and then get all the adhesive-laden solvent removed before it evaporates and re-deposits the adhesive back on the substrate.
All while using a solvent that does not damage the substrate, or react with the adhesive.