it does the same thing on my 05  it is caused by the engine not getting hot
enough such as short trips. it you take it on a long trip like 10 to 15
miles and then look at the cap you will see the foam has cleared up, nothing
wrong with engine

Why do you change oil so soon?

They have changed the formulation of motor oil to increase the life and
decrease the consumption rate of natural resources. I believe the
recommended change interval is 7500 miles, but I accept that this makes you
uncomfortable. I suggest that 5000 miles on a load of motor oil is
reasonable. I actually would suggest that the recommended change interval is
giving you less life on the oil than it is really good for.

Think of the manufacturer's view. They have to replace the motor if it does
not last for the warranty period, so they are going to hedge their position
by changing the oil sooner than is needed, rather than later. So, if they
say to replace the oil at 7500 miles, logic says it should really last more
like 10000 miles. I would not begin to suggest you go 10k on yoiur oil, but
I see no reason to not go at least 5k.

If it takes yoiu an year to log 3000 miles, then changing at that interval
makes sense, but if you commute to work in this truck and rack up 5000 miles
in 4 months, then the longer change interval is called for. You are wasting
money and oil to change at 3000 miles, unless it takes a year to log that
many miles.

As for the foaming, are you seeing foam, or a few bubbles stuck to the cap?
Foam in the oil is normally seen when you pull the dipstick while the motor
is running. The oil level at this time is un-readable, but the presence of
foam is easy to see. A couple of large bubbles is normal, foam is the
presence of lots of bubbles, very tiny bubbles.

Do you do lots of short trips?  

Moisture is a normal by product of gas engine operation, and it can
build up if not allowed to evaporate.    All of my vehicles do this if
I don't get them up to normal operating temp and speed, and keep it
there for at least 20-30 minutes, on a regular basis.  

My commute is only ~ 4 miles, so I normally bicycle to work.  Most of
my errands are inside the same 3-4 mile circle, so I often bike those,
too.  When the winter gets extra cold, and the road shoulders are icy,
I have to drive, so I see it in the vehicles that only do the short
trips.     I have a '99 Jeep Wrangler with 59k, had an '01 Subaru
Outback, and an '05 V6 Tacoma with 18k, all would display the foaming
under the right conditions.  I use Mobil 1 in everything.

Pick a grocery store in the next town for your weekly shopping trip.
If someone in your house drives farther, you could also swap one day a
week.

I noticed this on my Honda Civic oil cap (Casterol oil)--never
considered it to be a problem.   Could be moisture.  After an hour
driving do you still see the foam?

What brand and viscosity of oil are you using?

Ed

my tacoma did this,, i changed to castrol syn-blend oil and it went away..
it says its formulated for short trips...

troy