I think I figured out the reason for the gushers (which are even worse with decaf, which I used this morning).

I was grinding, WDT, and then before taking the funnel out, I'd whack the PF 5-7 times one the counter (I mean whack!), then whack it a few more times to even out the gap in the sides left by the funnel.

This time, I gave the PF two gentle taps, then leveled with my finger, before tamping. The shot was clean (i.e. no sputtering) all the way through (i.e. started dark and gradually got lighter until I cut it off around 35 sec, when it went totally blonde). Much better result.

As usual, the problem was on this end of the machine.

But as for temperature. I haven't measured the brew temp yet (have to find a styro cup around here somewhere), but I think my machine runs way too hot. I've been using a cooling flush of around 5-10 sec, and seem to get much nicer shots that way.

Next step is to measure the temp, and see where we're sitting.