"It’s been an incredible week of testing for us because we’ve done more mileage than we ever had before," the Briton told reporters at the Circuit de Catalunya before handing over to German team mate Nico Rosberg for the afternoon session.
Rosberg did 86 laps on medium tyres and said the car felt quick as well as reliable, even if Mercedes will not start exploring its true pace until next week's second test.
"Before we came here the team were talking about doing 800km a day and I was thinking they are crazy. I’ve never done that in the past...I've never had a week like this when the car has just kept going on and on and on," said Hamilton.
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Hamilton did 342 laps in total, 156 of them on the first day when the car was still fresh out of the garage. That works out at 1,592km, more than five race distances at the Spanish Grand Prix circuit.
With the V6 turbo hybrid power units now in their third year, reliability has been much better across the field than it was a year ago with far fewer red flags to stop the track action.
Even so, champions Mercedes have far outstripped their rivals in mileage terms, a better benchmark at this stage than outright pace because cars can have different fuel loads.
Ferrari's Kimi Raikkonen was fastest on the final day, ahead of Red Bull's Daniil Kvyat.
"The car looks fantastic," said Hamilton. "Obviously we don’t know the pace of the car just yet but what we can say is that it’s gone the distance and that’s half the battle."
McLaren's Fernando Alonso, a double champion who had a nightmare 2015 due to the under-performing Honda engine, had his spirits lifted on Wednesday when he managed 119 laps.
They dropped again on Thursday, with the Spaniard managing only three laps in the morning and unable to set an official time due to a water leak in the Honda power unit that occupied the mechanics for the rest of the afternoon.
"Today was disappointing after starting the first couple of days of the test so positively," he said. "It's not a major problem and will be fixed in time for next week's test."
Ferrari, closest rivals to Mercedes last year, have looked quick with Sebastian Vettel fastest in the first two days and Finnish team mate Raikkonen sounding happy enough as well.
"I am sure it's going to be a better car than last year's," he said. "We are happy so far even if we know there are still a lot of things to do."
The season starts with the Australian Grand Prix in Melbourne on March 20.
(Editing by Tony Jimenez/Toby Davis)
