Currently I'm using Meguiars White Wax (carnauba wax). I just waxed my car last Sunday. 2 days later, on Tuesday, it was a very heavy downpour at the place I park my car when I work. Then when I went to collect my car, I noticed that there are a lot of dark water lines washed down my whole car. It seems the wax is not working well in protection at all. Those looks like the wax melted and mixed with dirt from the rain water.

And today I washed my car. It seems to be those dirt are sticking to my paint. @_@ Washed but cannot help much. After washing, I used Meguiars UQD trying to clean up those stains. Took SO MUCH of effort to clear those dirt marks.

I wonder, is the "carnauba wax" can be melted and become even a dirt magnet? Or it is supposed to be melted and washed away, and those dirt marks are due to no more wax protection on my car?

I'm just going by past experience and observations with Megs other waxess/selants here as I haven't use Megs White Wax before.

First, a question, how's the front and rear windscreen? Are they as contaminated as the paint? Are the glass also more difficult then normal to clean? (don't compare with paint....just the glass only). If so, then it's in the rain...exceptionally dirty rain with lots of pollutant picked up during the downpour. Localised incident.

Second, I'd have to say that Megs are top notch with their polishes, cleaners and dressings but their waxes/sealants are mostly a bit of a disappointment to me. They just don't last and I do feel that the protection provided aren't that suitable to our climate. I've tried a few of Megs waxes and sealants (except for those Ultimate range) and they're quite prone to 'staining', especially if exposed to our hot sun right after rains. Yeah....and those stain aren't easy to remove by normal shampoo wash - need to use cleaners (e.g. all purpose cleaner).

But it surprises me when you say it took much effort to remove them with UQD. I've used UQD and it's pro range equivalent M135 and I'd say it's one of the 'strongest' QD in the market with great cleaning abilities.

I can only assume that it's the wax itself. Either the protection is to weak and easily get contaminated or it's already contaminated at the start. Megs White Wax is marketed as an AIO (All In One) with cleaner, abrasives and wax. Normally, AIOs aren't that durable in term of protection. When you're applying the wax, did your applicator gets dirty? If so, then what you're applying onto the paint is also 'contaminated' and will not perform at it's best. Try reapplying, say, on one half of the front hood or boot lid again. This time do two rounds. 1st round is to clean the surface and remove all the contaminant and second round, without pressure on the applicator pad, use it as if you're applying a wax/sealant.  Leave it for a half an hour or so before buffing off the access residue. See if there's any difference in protection or durability.

At this stage I can only offer troubleshooting steps as, like I said, I haven't tried Megs White/Black Wax and don't own a white car. Maybe acefreakz can chime in with his experience in maintaining his whitey with an AIO.