Spark plugs

Bad head gaskets will cause this also a bad intake manifold gasket CAN but not likely will.

rust color is not un-normal on a spark plug. A quick check is remove the valve covers and if you see a foamy substance you have a leak.

Under normal circumstances the ideal color of the deposit on the plugs is a brownish color this may be with a slight bit of light "fuzz" powdery deposit. Darker color or blackish may be an indicator the plug is too cold of a range. White or light gray or burnt look indicates the plug range is too hot. I've always thought it would be better to match the heat range or type of plug to the individual cylinders. Hotter or extended tip into cylinders that are burning dark. And colder range into cylinders that are burning too light. Rather than the norm of one "type/range" fits all.

Thanks for this addition. That is great info, and I am sure others will benefit from this.

I see the original response did not contain a lot of detail, so I am going to attach a little bit more.

Rusted plugs is not uncommon on vehicles that are kept outside or in high humidity environments. Also, it is common when they are not changed on a regular basis.

So clearly it is important to change the plugs when they are supposed to be changed because if the threads get rusted then it is very difficult to remove them.

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

I am attaching some pictures and charts that will help with determining possible causes of plug damage. This first chart is for the tip of the plug and the second picture shows normal rust that can happen on a plug that has not been changed in a while.

Please let us know if we can assist any further.

Thanks again.