coffee colored tiny blobs on coolant cap???

[Eddie25]

Decided to check the coolant level today, when I decided to open the cap and look through the threads of the coolant resovoir cap. Long and behold, there were little brown blobs spread about on the threads of the cap. Curious to know I too some between my fingers and found it is was rather oily. Please don't tell me I have oil in my coolant. From the outside of the tank and even looking through the threads of the cap the antifreeze looks a healthy green.

So what the [censored] is this brown sludge and how did it get there, if anyone could be so kind to answer. I haven't removed the cap in a while and was shocked when I saw this. Could it be because the weather here is constantly changing from rain to cold to snow to warm? And also because I drive less than 5 miles a day. Just like the crud that was developing under my oil filler cap because of the reasons just mentioned. I have taken my car out on longer rides but lately I've been doing alota of overtime at work and haven't had a chance to take her out. Please someone tell me this is normal.

 

[Doog]

Replace your cap it is leaking air into the system.

 

[Carbon]

Originally Posted By: Doog
Replace your cap it is leaking air into the system.

I don't think caps are designed to block air coming in. They don't want a vacuum in the system.

 

[2oldtommy]

the vacuum in the system should pull in coolant from your resevoir bottle.Is your resevoir at a level between 'max.' and 'low' so that it never goes below 'low' when the engine is cold? What is showing in the resevoir bottle? If it is not clear, you are due for a system flush as the first step of system maintainance. FWIW--Oldtommy

 

[Rock_Hudstone]

I have two GMs, over ten years old and running conventional green coolant. I find its not unsual for a very small amount of light tannish, (not brown), goop to accumulate on the underside of the radiator cap while the coolant itself looks fine. Especially if unopened for a long period of time and/or the coolant is due for a flushing.

Been doing it for years and many miles with no ill effects. Could be the natural break down of the coolant over time, it is a petroleum based product, no?

Large amounts would call for further inspection of course.

On the other hand, signs of coolant in the oil means trouble, that can trash an engine in short order.
Best place to look is on the PVC valve or peak inside the valve cover area through the oil fill cap. I always check both ever oil change.

 

[Towncivilian]

Originally Posted By: Rock_Hudstone
Could be the natural break down of the coolant over time, it is a petroleum based product, no?

Antifreeze is usually ethylene glycol based.