Start in first gear.

This is the first time it happened.
The weather temp.is mid 70s.the traffic
is stop and go and my eng. temp.went to about
85.I notice that upon take off,my car will
move a little and shift to 1st gear.It only
happen when the fan clutch start howling.(engaging)
Can this be the result after I change my
trans fluid?(1st change since I bought the car 2yrs ago.)
No power loss,In fact I love the feeling of starting in 1st.
It goes back to normal when the temp. needle fall back
to 80.Can this be harmfull to my eng.? Is there any
adjustment? Thanks.

Clauser1