McLaren and Honda swiftly denied rumours of a split between the Formula One team and engine supplier after their first positive day of pre-season testing in Barcelona.

The opening two days at the Circuit de Catalunya saw oil system and engine issues for Fernando Alonso and Stoffel Vandoorne, but they were finally able to run problem free on Wednesday - albeit after an engine change.

That power unit the stifled Vandoorne will be assessed at Honda's factory in Japan overnight to understand the problems he encountered.

Alonso completed more laps than McLaren had done across the first two days with the new engine, the Spaniard racking up 72 as he clocked the 10th fastest time.

Off the track rumours emerged that McLaren were unhappy with the Honda reliability after similar problems last season, but racing director Eric Boullier was quick to dismiss them.

"We are supposed to ditch Honda?," he asked. "No. There is no plan at all.

"We have had many issues. None of them are fundamental. All of them are fixable. I am not sure we know all of them yet because [Tuesday's] engine is on the way to Japan.

"[On Wednesday] finally we can run, we have some other glitches, the usual ones you get on day one. But we have them on day three.

"It is a new layout of the engine from Honda and obviously some unexpected glitches but nothing is fundamental."

While Alonso will have been pleased to stay problem free, the pace was not there in the McLaren as once again Mercedes topped the timesheets - Valtteri Bottas going two tenths faster than Ferrari's Sebastian Vettel.

Bottas got another 75 miles in the tank for the WO08, while team-mate Lewis Hamilton took over in the second part of the day and completed a full race simulation.

Vettel racked up an impressive 139 laps on a productive day for Ferrari, while Red Bull and Renault also showed good pace, but there was more troubles for Lance Stroll in the Williams.

The rookie crashed his car on Tuesday to bring an abrupt end to their session, and he had another spin on Wednesday - however he was able to get through 98 laps.