Jerez F1 test: McLaren-Honda halts Tuesday running after problem

The Woking-based team had its most encouraging morning of the test so far on Tuesday, as Alonso completed a total of 32 laps.

It came after a frustrating first two days where the Spaniard and his team-mate Jenson Button had managed just six laps each.

But having appeared to make some progress with its power unit, a problem on the Honda turbo engine has forced the team to abandon running for the day.

A tweet from the team said: "We've had a loss of cooling water pressure and have removed the power unit for inspection. That's a long process, so it ends today's running.

"We can replace those components ahead of running tomorrow. The issue was promptly spotted by Fernando on an out-lap - so quick to trace."

McLaren has renewed its partnership with Honda for 2015 in a bid to get itself back to the front of the grid.

Despite a difficult first week, the team has remained bullish that the potential of its aggressive new car and engine will deliver results.

Racing director Eric Boullier said earlier this week: "Being brave and ambitious means we're not reliable.

"I want to be cautious on this because every time we try to fix one [problem], we open up something else further."