My radiator cap appears to be stained on the outside.

My car is not overheating & it doesn't appear to be leaking.


How it started?

had the car for about 8-9 months. i noticed the reservoir fluid went down a notch so i open the radiator cap to check today. it was a little hard to open but i opened it. (by hand) the fluid looks good & all.

i checked the cap to see if it is springy & it is. i went ahead & purchase another cap from dealership & will be replacing it. but wanted to know how the stain came about.

NOTE: today was the 1st time i opened the radiator cap since i purchased the car. the stain appeared today after i ran some errands & just check & there was the stain. so yeah after opening the cap & putting it back on.


thanks in advance