I have a friend that works at a local detailer shop.
He said that when they hand wash dark colored cars, they put a
1/4 cup of Vegetable oil in the soap bucket along with the usual car wash soap.

Has anyone else heard of this??

He claims that it removes more dirt and makes the water run off better so you get less water spots.

 

Never heard that, but have heard of something a little bit similar years ago.

There was a time when, believe it or not, people added kerosene to their wash buckets. I remember people doing this in the 60s.

 

Yep! I learned that kerosene trick while camping in Canada. Car was routinely covered with bugs and other night muck, and I was always trying to clean it.........It's a bear to remove if it dries and gets baked on. One of the locals suggested putting a half-cup of Kerosene in my bucket. The bug gunk not only ........ uhh ....... "flew" off the paint, but it left my finish with a nice sheen. No doubt it stripped off any wax, but I didn't care during that trip. Nowadays I keep a quart handy. When the truck is particularly grimed up, I add a half cup to my bucket and that dirt/gunk/bird dook/tar/etc. just comes right off. I also re-wash and wax. It's a little extra work, but my finish still looks perfect after a year.

 

I'm in the Carwash business and what you are describing is what we call "cheater wax" because it's cheap and really doesn't do the job of a wax but it looks nice. It will kinda blur the windows though. Most professional Carwashes don't use it anymore but it won't hurt anything if you want to use it in your bucket. Wd40 is great on bugs and grease also.

 

I tried this over the weekend. I put the Veg. oil in the wash bucket after washing the top and windows.
This made no difference.
It was bogus information.