The ExxonMobil gearbox oil ‘taste-test’

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You’ve probably seen those old TV adverts where a sparkle-toothed presenter doorsteps an unwitting housewife to ask her to tell the difference between two household brands. Whether it’s between two competing brands of cola, laundry detergent or margarine, the inference is clear: even when blindfolded, the quality of Brand A sets it apart from Brand B.

But could we really perform a blind taste test using samples of Fernando Alonso and Jenson Button’s used gearbox oil and tell them apart?

We could. And we did!

It doesn’t sound possible, surely? After all, the oil is poured into the gearbox, swills around between a Formula 1 car’s eight forward gears and one reverse gear, and is then drained out after a busy few hours, right?

But McLaren-Honda’s ExxonMobil scientists can look at oil samples taken from Fernando and Jenson’s gearboxes and immediately tell them apart without the need to read the label.

Why do we need to do this? Because testing gear oil is a quick method of checking the health of a gearbox.

So what are the ExxonMobil scientists actually analysing? They’re checking for tell-tale signs of wear within the gearbox by measuring the amount of microscopic metal particles the in the oil. These are generated as a result of contact between the gears and bearings.

The lab equipment will detect everything from Aluminium to Zinc, and some rather more exotic metals in between – but because many of the gearbox internals are made from high-strength steel, the primary element of interest is Iron: too much Iron content in the oil suggests a potential wear issue within the gearbox.

And the equipment is so sensitive it can tell the difference between Jenson and Fernando’s samples because each driver produces his own recognisable ‘signature’.

“There are tiny, tiny differences between the drivers,” explains Bruce Crawley, ExxonMobil’s Global Motorsport Technology Manager. “But through clever analysis we can tell from whose gearbox the oil has come. We do this by looking at the sub-micron-sized particles (1 micron = 0.001mm) in the oil, which are measured in parts per million.”

Where do these metal particles come from? The pressures within the gearbox case are intense; measured on a scale usually reserved for earthquakes, or growing artificial diamonds. Everything meshes and rotates at incredible speeds and, with that much hot metal clashing, some debris is inevitable. In fact, the only thing that prevents gearbox armageddon is the layer of gear oil, half the thickness of a human hair, separating 750 moving parts within the casing.

At maximum revs, the Mobilube SHC racing gear oil is lubricating 15,000 gear teeth contacts every second under pressures so high and so intense that the oil undergoes a phenomenon known as ‘phase-change’, transforming from liquid to solid, to semi-solid and back to liquid again many times a second as the gear teeth rapidly engage and disengage.

Think about that for a moment. Solid oil. That’s not science fiction – that’s reality…

In the modern era of seamless shifting and incredibly smooth, electronically controlled gear-changes traditional wear has been largely eliminated – and with the drivers using identical gearboxes and the same software, the differing results from Jenson and Fernando’s samples initially created a puzzle for Mobil to solve.

“At first we weren’t sure why that would be,” says Bruce, “because our latest gearbox oil has improved wear-rates by over 50 per cent in the last three years, so we’ve pretty much eliminated any wear on the gears and the dog rings.

“And, besides,” he adds, “we don’t like mysteries…

“So we discussed the situation with the race engineers to find an explanation. It turns out the drivers like to set up the car’s balance and handling differently, and this affects the loadings on both the differential and the gearbox – and this is what we see in our oil analysis.”

There’s more than one way to get a lap time, with Jenson and Fernando going about their trade in different ways: one likes a smooth, controlled car on corner entry; the other prefers a little bit of rock’n’roll (you can probably figure it out).

These distinct styles require contrasting settings in the car’s differential, and it is these individual diff settings that produce contrasting levels of gear-loading. Not to the extent of altering the performance or longevity of the gearbox but enough that, to the highly trained eyes of our Mobil experts, it’s as clear as night and day.