Ahead of today's session the air temperature is 28 degrees C, while the track temperature is 30 degrees. The mist that covered the circuit just a short while ago has burned off and the temperatures are rising.
While Nico Rosberg topped the timesheets in FP1 yesterday, it was Max Verstappen who led a Red Bull 1-2 in the second session. However, with neither Mercedes driver running the supersoft tyres it was to be expected that the silver cars wouldn't be leading the way.
The world championship leader will start tomorrow's race from the back of the grid having been hit with a 30-place grid penalty after his team fitted new two new turbochargers and MGU-Hs. With an eye on the demands of the coming races, not to mention an engine upgrade, further penalties are sure to follow.
Indeed, since first light, Hamilton's crew have been working furiously on his car.
Fernando Alonso has also been hit with a penalty following a change of engine and consequently the Spaniard will start from the back alongside his former teammate, while Marcus Ericsson has a ten-place drop following a change of turbocharger.
With an eye on the unusually high temperatures there are fears that those teams who have gone aggressive in terms of their tyre strategy will rue the day, Ferrari one of several that appears to have placed a lot of faith in the red-banded rubber. Kimi Raikkonen claims his supersofts couldn't last a full lap.
Other than the Red Bulls, also looking strong yesterday were the Force India pair, Nico Hulkenberg and Sergio Perez, who, as ever, look likely to benefit from a more conservative tyre strategy.
Despite incessant complaining from both drivers, particularly Romain Grosjean, Haas is looking good, while McLaren might also pull something out of the bag.
Following a might impressive opening session it was back down to earth with a bang in FP2 for newbie Esteban Ocon, though the rookie's FP1 pace appeared to fire up teammate Pascal Wehrlein for the second session.
The lights go green and Gutierrez leads the way, followed by the Ferrari duo.
Gutierrez posts the first time of the day (49.923) but is subsequently involved in a nasty incident at Eau Rouge with Wehrlein which sees the German forced off track. The Manor driver is far from happy.
"Unbelievable, he should get a penalty," says the German, his team assures him that it will speak to Charlie Whiting.
Elsewhere, Rosberg goes quickest (48.880), ahead of Grosjean, Massa, Gutierrez - who is now under investigation - Wehrlein, Ocon and Ricciardo.
As Verstappen heads down the pitlane, an orange smoke bomb is let off on the run up to Les Combes.
Sensor installed at Raidillon reveal that Perez has run wide as the FIA continues its crackdown. Moments later Ricciardo also runs wide.
Mercedes confirms that Hamilton has had another power unit installed.
"Lewis has fitted ICE 6, MGU-K 6, MGU-H 8 and TC 8. This completes the changes for the weekend," says the German team. "It also means a notional further 25 places worth of grid penalty."
Verstappen, whose car is smothered in flo-vis, is running very slowly. "I have no power," he says.
A 49.115 sees Rosberg go second, ahead of Hulkenberg and Perez, as, seventeen minutes into the session, only 11 drivers have posted times.
Back in the pits, there appears to be a major problem with Verstappen's car, the crew swarm over the car like worker ants. Having already had a new gearbox this weekend, without penalty, if it's a gearbox issue requiring another unit that would mean a 5-place penalty.
Hamilton runs wide in T4 (Raidillon) as Perez and Ricciardo are warned having done it twice.
"Straight into race sim work for Lewis with practice starts and cruise laps," reveals Mercedes. "No need for blistering times today. When you're starting from the back, it's all about race pace."
No sooner has Vettel posted 48.502 to go quickest than teammate Raikkonen bangs in a 48.406.
Magnussen goes eighth and Palmer twelfth, both, like most, are on the supersofts. Rosberg and the Force Indias being the main runners on softs.
In quick succession, Grosjean, Wehrlein, Palmer and Magnussen run wide in T4.
At 'half-time', Alonso, Verstappen and Ericsson have yet to post times.
Vettel is not impressed when he is blocked by Magnussen at Blanchimont. "What an idiot," says the German. "Honestly, what an idiot. It's called free practice, who gives a ****?"
Hamilton, on the softs, is lapping in the low 1:55s, around 6s off the pace as he continues with his own programme.
Having gone quickest in S2 - where Ferrari is particularly weak - Ricciardo goes quickest with a 48.189.
Alonso and Ocon are the latest to fall foul of T4.
"Suddenly got big oscillations on upshifts," warns Button. "It actually gets worse when you go slower," he adds, "or maybe not."
Check out our Saturday gallery from Spa, here.