Why does gearbox oil need changing?

Many drivers service the engine religiously and never think about the gearbox. Yet the gearbox works just as hard and relies on its own oil or fluid to stay healthy.

Here is what the fluid does, when it might need attention and what to ask. We Fit Any Clutch Cornwall carries out fluid changes as part of its gearbox work, and can come to you across Cornwall.

What does gearbox oil actually do?

Inside the casing, gears mesh and spin at speed, bearings turn and selector parts slide. The oil forms a film between them, reducing wear, carrying away heat and holding tiny metal particles in suspension. In an automatic it also transmits hydraulic pressure that operates the internal clutches.

Over time the oil breaks down, collects particles and loses its protective qualities. Worn oil means more friction and more heat.

How often should it be changed?

There is no single answer. Some manufacturers specify intervals and others describe the fluid as filled for life, but conditions matter. Towing, heavy loads, short journeys, stop-start driving and hilly routes all put extra stress on the fluid.

Check your handbook, then consider your use. Cornwall driving, with its hills, summer queues and loaded holiday cars, can be a demanding mix. The mechanic can advise on what suits your vehicle, rather than relying on a generic figure.

What are the signs the fluid is tired?

Stiff or notchy gear changes, a whine that was not there before, difficulty engaging gears when cold and a burnt smell are all clues. In an automatic, harsh or delayed shifts can also point to degraded fluid. Dark fluid or fluid containing fine metal glitter is a worry.

A fluid change can improve shifting if the oil is the problem, but it will not repair worn parts. Sometimes the fluid reveals the true condition of the gearbox.

• Stiff or notchy shifts
• New whining
• Burnt smell
• Dark or gritty oil

Is an automatic fluid change different?

Yes. Automatic fluid is a specialised product, and different gearboxes call for different specifications. The wrong type can cause shifting problems or damage. The correct level and temperature at the time of checking also matter, which makes a careful procedure important.

Some automatics have a filter or a sump that should be dealt with at the same time. The mechanic will explain what applies to your gearbox.

Can a fluid change cause problems?

On a healthy gearbox it should not. Occasionally, on a very high-wear automatic, new fluid can expose existing weakness, which is why some mechanics want to look at the condition of the old fluid first. A careful approach and the correct specification reduce the risk.

If your gearbox already shows symptoms such as slipping or harsh shifts, mention it before the work. The mechanic may suggest diagnosis ahead of a change, so that the cause is not masked.

What should I ask before a change?

Ask which fluid specification will be used, whether the filter or seals are being checked, and what condition the old fluid is in. A good mechanic will show you or describe what came out.

If the old fluid shows signs of heavy wear, that is valuable information and may lead to further checks. Message us with your vehicle and driving pattern and we will talk it through.