Formula One: Hamilton prays for rain at blast-furnace Hockenheim

Hamilton arrives at the paddock of the Hockenheim racing circuit. PHOTO: DPA

HOCKENHEIM, Germany (AFP) - Lewis Hamilton fears that a prolongation of Europe's record-breaking heatwave could upset Mercedes bid for glory at their home German Grand Prix this weekend.

The defending five-time world champion, and current series leader, told reporters Thursday that he was hoping for rain and admitted that if the sweltering conditions continued Mercedes would be in trouble.

"I'd imagine, if it stays this hot, we're going to be in trouble," said Hamilton.

"We've got these hot races coming up, which are obviously not so easy for us so it's going to be a challenge.

"It's definitely a good thing if it rains! There's not really much we can do (about cooling problems) as it's a much bigger design issue that we have when it gets hot, so it's not so easy to change... Hopefully, this weekend will be ok."

Hamilton enjoyed a famous victory in last year's race when he won from 14th on the grid after title rival Sebastian Vettel crashed out of contention while leading in heavy rain.

But he struggled home fifth, with team-mate Valtteri Bottas third, in high temperatures at the Austrian Grand Prix last month when Mercedes were defeated for the first time this year.

Local weather reports recorded 40 deg C in the Hockenheim paddock on Thursday.

"Clearly it (cooling) is a big weakness in our package," said Bottas.

"We have a new upgrade for the cooling systems so that should be more efficient - and should give hopefully quite a few degrees of margin, but I'm not sure anyone expected to be racing in 40 degrees."

Bottas is 39 points behind Hamilton in the championship following the Briton's home win at Silverstone two weeks ago, his seventh victory in 10 outings this year.

That spell of form has delivered his best start to a season.

"I was just reminiscing about my McLaren days and I think the most I had in a year was five wins," said Hamilton.

"Over all the years, I think we've maybe had 10 in a season, but never seven in the first 10 so it is definitely an outlier and something we are proud of."

Hamilton is the first driver since Michael Schumacher in 2004 to win so many of the opening 10 Grands Prix.

Schumacher ended that 18-race season with a record 13 wins, a target for the Englishman in the remaining 11 races.

He added that he would work on improving his qualifying as he seeks to add to his record 86 career poles.

"There are always things you can learn from these races, even though the last one was pretty strong, but there are still areas that can be better," he said.

"For example, qualifying is still not perfect yet. So I've got to work on that, but in general the race pace has been really strong."

Hamilton added that he also expects to see Ferrari and Red Bull improve their pace and said he welcomed the prospect.

"I hope it gets closer through the year," he said.

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