I had something sort of similar a few years ago. The seals on the clutch
master cylinder were on their way out and in very cold weather they would
contract and give me the symptoms you describe --- when the van heated up,
the seals would expand and be fine (master cylinder is behind the dash and
is therefore warmed by the powerful heater and my occasional profanity
:-). May not be your problem but it does explain a possible relationshsip
to temperature. Means your master cylinder is on the way out and you need
a new one --- may as well do the slave cylinder too because they tend to
go in tandem. Note: My version of cold weather was below zero
fahrenheit............

Cheers,
Doug

> The last few cool/cold (below 40 deg. or so) mornings I've gone out to
start
> the bus, the clutch has refused to disengage from the flywheel. I can
shift
> into neutral, start the bus and pump the clutch a few times and it
releases
> like it should. No further problems once underway. What should I look at
as
> the cause for this? My first thought was the slave cylinder, but the
pedal
> doesn't feel any different than under normal conditions. TIA-