I know that this is a very common problem, but does it always mean that you have a blown head gasket? I have had this problem before and then it went away. I changed my oil today and some was on the oil cap as well as in the drained oil. My antifreeze seemed to be low, but my truck is always low on antifreeze for some reason. While underneath my truck, I saw an electrical wire with antifreeze pooled up on it. The water pump doesn't seem to be leaking and neither are any of the other common places for leaks. I had thought it was the head gasket last time I saw this film, but the problem went away. Any thoughts?

 

Sometimes when I used to let my truck sit for a few weeks it would do the same thing...chalked it up to basic condensation under the cap. its still a problem, though, since if there is condensation there, its also in your gas tank(s) your oil pan, transmission, etc. After discovering that, I was pretty diligent about changing fluids pretty regularly. Never had any issues related to that, so I'd have to say it did no harm. YMMV...
Roger

 

Chances are it is a head gasket or a cracked head, pressure test it then proceed with what that uncovers. Stop leak might fix it temporarily but it also plugs things that arent supposed to be plugged.

 

I had went to Colorado for a week so it had been sitting. But, I might continue to get it pressure tested if the problem persists.

 

I always get that when temps are cold.

 

When it gets cold outside my truck always get this and during the summer is fine. I only take short trips under 10 miles usually so that is probably part of the problem also, because I went on a 2 hour roadtrip in the cold and when I got there the cap was dry.

 

It is quite common to get a somewhat milky residue on the filler cap without a major issue such as a head gasket. Normal condensation from heat and cool cycles (particularly in colder weather). If concerned about a head gasket, go ahead and conduct appropriate tests to make sure, but I sure wouldn't just assume it's bad and start dumping stop leak in it! As for possible sources of coolant loss, one that is often overlooked is frost plugs. Would eyeball them as well.

 

I agree, I had this problem before with the film and I didn't react. I waited to see if it persisted, which it didn't. I never put Stop Leak in any of my vehicles. It gums things up, such as radiators that is horrible. I would rather put an egg in there to stop the leak like on myth busters than a can of Stop Leak

 

I found the same thing on my oil cap today and this just made me feel much better. I thought head gasket for sure,but the oil looks fine,just on hte oil cap.

 

Replace the PCV valve, and chances are the goo on the filler cap will disappear.