Any ideas what the orange/rust color is in the photos below?

As well, what could be the source of it?

There is a lot of hard gunk buildup here.

Here is the image.

enter image description here

  • Looks more like Chevy Orange. What car/engine is it?
    – PeteCon
    Commented Sep 8, 2016 at 3:39
  • It is a Kia Pregio Van Commented Sep 8, 2016 at 4:27
  • Is it not just the remains of whatever paint was originally used on the block?
    – Nick C
    Commented Sep 8, 2016 at 9:34
  • Did you notice any coolant leak?
    – Alimba
    Commented Sep 8, 2016 at 9:55
  • 1
    If by odd chance it is a weld repair, they are commonly done for various reasons depending on the engine. Certain engine blocks have casting or design flaws that can lead to small cracks in the block walls, some are repairs for over stress or over heating. Some even relate to engine mount issues. Commented Sep 9, 2016 at 14:48

3 Answers 3


The color looks astonishing similar to lead tetroxide. Decades ago used as a metal rustproofing and paint primer. Originally the golden gate bridge was rustproofed with that stuff. Now virtually everywhere prohibited because of his toxicity.

Are there any signs that this red colored stuff got painted on? That being the case it could be possible that some previous owner (plumber, boiler mechanic) was trying to rust proof some weld repair and consequently endangering the next unfortunate guy who is working on the engine.


I'm not certain what it is but I agree with @Pete that it does look a lot like grunged up Chevy Orange. The peculiar part is how it is spot painted. I'd like to upload an image that samples a couple of the orange areas and lay them side by side with other nearby patches. You can see how I blocked out a white background in the lower right corner and copied little patches of image to that region for side by side comparison. Hopefully the size and orientation of the rectangles are easy to spot in the parent image.

I'd say clean up the area and upload some additional images. It's an interesting mystery.

sampling various patches


Your diesel engine has burnt some sort of substance on it from the radiator area rearward. The pinkish orange colour could indicate auto fluid mixed with coolant, this may indicate a cracked transmission oil cooler (within the radiator) mixing with coolant and blowing out from the radiator or overflow tank. Not sure without smelling or checking levels, also the front base of the rocker cover has definitely seen heat also, you need to start troubleshooting by checking all fluid levels.

Cheers Hutch

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