Not going to lie, I don't understand rust. From pictures of rust spots how does one know if it's harmless surface rust? How does one decide if rust shows the car is being eaten from the inside out? I've attached two pictures of rust spots and was wondering if anyone here could give their opinions.. Can you tell me the tale of two rusts? Thank you greatly!

https://assets.hemmings.com/uimage/5...0@2X.jpg?rev=1

https://images.craigslist.org/00V0V_...Hl_600x450.jpg

 

If the parts aren't painted it can sometimes be clear just by scraping with your finger nail (be careful). If its powdery and you can feel a hard surface then its probably only surface rust.
If its scaly and comes off then more steel has been lost.
After that the best way is to use a screw driver to push into the panel if its badly rusted then it will go straight through. This is the test used in a UK MOT.
If its painted, and the paint is bubbled then the screw driver test is best and or sand away the paint to get to the steel / rust.

 

Since I have owned dozens of rusty cars I guess I am somewhat of an expert. The undercarriage photo is probably nothing to worry about. If you are picky you could give it a quick one over with a wire brush and a can of flat black spray paint. I would probably not even bother with that.

The bubbles on the door are a whole different ball game. That is definitely coming from the inside and is probably going to require surgery, welded patch panel, etc. A guess is the window seals are shot, water leaked down inside the door making a warm wet environment and has been rusting ever since.

That having been said, I have a series 3 with some little rust bubbles under the windshield. I never drive that car in the rain. As a mater of fact, I don't even get the car dirty enough to wash with water so the rust bubbles are just going to live there as long as I own the car with no changs. I love the car, warts and all so don't automatically rule out a car with rust.

 

Picture 1 is surface rust, cause by a damaged coating. A simple sandjob and recoating with protective primer and body coating will suffice.


Picture 2 might be rust from the inside, but can also be caused by damaged paint. If the paint is undamaged, this rusty spot needs to be mended by cutting out the damaged part generously and welding in a new piece of sheet metal. Then the usual wash primer, sanding surfacer, base coat and clear coat...
You could also sand out the rusted area and go to the filler / surfacer directly, but that is not my preferred method. If you don't remove the entire "tumor", the rust will spread again soon...

 

There is no door that stays completely dry from the inside in any car, new or old. That is why the door panels are proctected by plastic splash sheets inside the door. There are holes in the bottom of the door, that allow any water to drain from the inside and to ventilate the inside of the door. Make sure that the holes are clear at all times. The door panels can also be covered in protecting wax on the inside, so that water doesn't affect the metal.

 

First off idrovetheepb, Welcome to the forums. Please post an intro in the new member area when time allows.(Link below)

https://www.jaguarforums.com/forum/n...-intro-must-5/


Not wanting to scare you, but what started out as a couple of little bubbles in the paint around my sunroof 12 months ago.(very like the picture below.)



Turned out to be this rust monster once uncovered.

 

Not wanting to scare you further, this is what I had to do to fix the rust damage around ALL windows on my car with "minor surface rust":

 

If you have seen it a few times on different cars in different areas you quickly understand what is going on when you glance at another car.

The first pic is light surface rust because the undercoating came off. Easily removed. Sometimes in dry environments this stuff just forms on the surface and ends up protecting the rest of the car.

Generally paint is on the car to protect it from rust, so if you have bubbles underneath the paint, there is a strong likelihood that the entire panel is rusted through at that location. Sorry if all I did was re-iterate what others already said.

Second is either completely through the panel, or existed on the surface before the door was repainted, if it was repainted. Either way, if it is enough to form a bubble, you can bet there is a hole through that panel somewhere. If there is a lot of moisture rust will tend to expand and break into pieces, which is what a "bubble" is.