Not really. Even when there is a leak internal to the
cooling/lubrication system the oil will still tend to eventually
concentrate in the overflow tank. Oil floats on water. The floating oil
will collect in the top of the main tank and when the coolant warms up
and expands the oil will be pushed out the cap hose into the overflow
tank. Then this oil will float in the overflow tank on top of any
coolant in there. When the engine cools it will suck coolant from the
bottom back into the main tank. In this way the overflow tank acts as a
trap for oil that gets into the system.

In your case I would still suspect someone put oil in the cooling system
but time will tell.

Mark

Michael Sullivan wrote:
> Since the oil was changed before the trip and it has sat in my driveway for
> a week, IF the oil was added before the trip, it would have traveled
> throughout the system by now, right? Can't think someone would intentionally
> do it.
> Michael in San Antonio
> 91GL AT 'Gringo'
> 73 Beetle
>
>
> On Mon, Mar 23, 2009 at 10:21 AM, Allan Streib <streib@cs.indiana.edu>wrote:
>
>> If it's only in the overflow tank that sure sounds to me more like someone
>> accidentally added oil there.
>>
>> Allan
>>
>>
>> On Mon, 23 Mar 2009 10:10 -0500, "Michael Sullivan" <
>> sandwichhead@GMAIL.COM> wrote:
>>>> OK...checked oil level and right between low and full.  Pulled the
>>>> hose from the overflow to the expansion and noticed some blue
>>>> antifreeze drip out.  When I lowered the hose  I left about 1/8 cup
>>>> flow out and all blue. Opened the expansion tank and it was a little
>>>> warm but all blue. Stuck a stick in there and no oil on the stick.
>>>> I am stumped how oil is in the overflow and not in the expansion.
>>> I will admit, sheepishly, that when my kid was ready to leave for FL,
>>> I had him run it to Firestone(ya, I know) for a quick oil change.  I
>>> got the Delo 400 here for the change after he returned but haven't
>>> got to it yet. Wonder if someone intentionally did it? Kid says he
>>> topeed off antifreeze w/a pre-mix I sent with him, but did not touch
>>> the oil. hmmm.
>