Which oil for drill rig gears to choose? Mineral, synthetic or semi-synthetic - a review of the parameters

The choice of oil for a drill rig's gearbox has a direct impact on the equipment's durability, operational safety and operating costs. It is a decision that should take into account the operating conditions, oil type, viscosity and compatibility with the excavator's hydraulic system, not just the invoice price.

What does the choice of oil for the drill rig gearbox depend on?

The choice of oil for a drilling rig's gearbox depends primarily on the operating conditions under which the machine actually operates. The intensity of the loads, the continuity of the operation, the temperature range and whether the drill rig is in seasonal or year-round operation are all important factors. The oil will behave differently under short cycles and moderate loads and differently under prolonged high torque operation, where viscosity stability, resistance to oxidation and the ability to maintain the oil film under difficult conditions are important.

Equally important are the manufacturer's requirements, the ISO VG viscosity used, the oil grade (HLP or HVLP) and compatibility with the excavator's hydraulic system that feeds the drill rig. In practice, you are choosing an oil not just 'for the gearbox', but for the whole system - so change intervals, cost per hour worked and whether the oil will retain its properties without risking accelerated component wear are also important.

Mineral, semi-synthetic or synthetic - which oil will actually withstand the operating conditions of your drill rig?

In simplest terms, mineral is the oil of choice when the equipment is running more quietly, temperatures are rather stable and you are keeping an eye on changes without 'pushing the schedule'. This solution is the cheapest to start with, but it is also the most sensitive to what is the norm in construction: temperature spikes, long working days and temporary overloads. Things like oxidation and a decrease in viscosity stability increase more quickly in mineral oil, which translates into a simple matter in the gearbox: a weaker protective layer when the going gets tough. On the other hand, if the rig is running 'humanly' and the service schedule is not wishful thinking just a rule of thumb, mineral can be a sensible choice - especially when low cost of entry and predictable product availability matters.

Semi-synthetics and synthetics come into play when your rig is living with the realities - once cold, once warm, once drilling in harder ground, once longer runs without a break. Semi-synthetic is usually a sensible compromise: you get better thermal stability and less frequent changes than in a mineral, but without the cost typical of top synthetics. A synthetic, on the other hand , is there to give you peace of mind in more severe scenarios: where resistance to temperature extremes, high viscosity stability and long service intervals are important. Synthetics tend to perform well over a wide temperature range and their service life can be in the region of 12,000-16,000 hours, which in practice means fewer stoppages for oil changes and less risk of the oil "going flat" when you don't have time for service. And a small but important note: if you are switching between oil types, do not add "something similar". Mixing oils with different additive packages can reduce protection and cause problems, so it is safest to do a full change according to the manufacturer's recommendations.

ISO VG 46, HLP or HVLP? How not to get lost in the viscosities and standards that determine the life of a gearbox

If you have a confusion in your head like "ISO VG 46 and next to it HLP and HVLP", rest assured - it can be sorted out straightforwardly. ISO VG tells you the viscosity at a reference temperature (usually 40°C), i.e. in practice: how "dense" the oil is under standard conditions. For construction machinery, ISO VG 46 comes up very often, because it is a viscosity that usually gets along well with mobile systems and the typical temperature range in Poland. And now the key - temperature changes the viscosity - when it gets warm, the oil becomes thinner, and when it's cold, it thickens and flows worse. Therefore, 'VG' alone is only half the story. The other half is the stability of viscosity at varying temperatures, i.e. how much the oil 'floats' with parameters when you have a chill in the morning and your equipment is warmed up in the afternoon.

This is where the HLP and HVLP designations from the DIN standard come in. In short: HLP is the standard for heavier, 'normal' work - the oil has anti-wear additives and can protect components in high-pressure systems well. HVLP goes a step further because it has a high viscosity index, meaning it maintains viscosity better when the temperature changes. If your rig is working outdoors and catching the typical Polish swings (colder mornings, warmer mornings, working at different times of the year), HVLP can sometimes be a choice that simply makes life easier: it reacts less nervously to temperature, and you have a more predictable operation and less risk of the oil turning out too thin or too thick at a critical moment. In practice, many mobile machine configurations do well with the HVLP ISO VG 46 variant, especially if you are concerned about stability. And one more thing: if the manufacturer of your drill rig or excavator requires specific standards - stick to the instructions. It's not 'paperwork', it's real-world compatibility with seals, operating pressures and the expected additive package.

Hydraulic drilling rig on an excavator - why the same oil needs to last much longer than usual

A hydraulic drill rig for an excavator does not have a separate, classic mechanical transmission and therefore does not run on a separate gear oil. The entire drive is based on a hydraulic motor, which converts oil pressure into rotary movement of the auger. This means that the drill rig uses exactly the same hydraulic oil that powers the cylinders, distributors and other components of the excavator system. In practice, the oil acts as a working, lubricating and cooling medium at the same time, and its quality directly affects the smoothness of the drill rig's operation and the durability of the entire system.

The problem arises when the drill rig starts to realistically work under load, because its use radically changes the conditions in the hydraulic system. The oil temperature can rise from a typical 50-60°C to as much as 65-80°C, the operating pressure jumps from a range of 150-200 bar to 250-350 bar, and the required flow rate often doubles. This causes the oil to age much faster, lose its viscosity stability and protective additives, and shorten change intervals by up to several times. Therefore, when working with a drill rig, the hydraulic excavator ceases to function under 'standard' conditions - and the oil, which was previously sufficient, very often proves to be insufficient with such increased operating parameters.

FAQ

Does a hydraulic drill rig have a gearbox that requires a separate oil?

No, the hydraulic drilling rig does not have a mechanical transmission. It is a completely hydraulic unit, driven by hydraulic oil from the excavator system rather than a separate transmission system.

What oil should I choose for hydraulic excavator drills - mineral, synthetic or semi-synthetic?

A universal choice is HVLP ISO VG 46 (high viscosity index), as it performs well in the changing conditions of the Polish climate. If you work in severe conditions, choose semi-synthetic, and for intensive use, synthetic.

Can I mix mineral oil and synthetic oil?

No, never mix these oils as their additives may be chemically incompatible, which will reduce the effectiveness of the protection and may damage the system. Always change the oil completely, do not top up with another type.

How many operating hours should I change the oil in the drill rig?

Mineral oil should be changed every 3,000-4,000 operating hours, semi-synthetic every 6,000-8,000 hours and synthetic up to 16,000 hours. For heavy-duty hydraulic drill rigs, the intervals can be much shorter - every 500-1000 hours.

Is synthetic oil always better and more economical?

Not always - although synthetic oil is more expensive (£60/L vs £17.50/L for mineral), its longer life (up to 16,000h) can make it cheaper per operating hour. For heavy-duty drill rigs, the minimal risk of failure sometimes justifies the higher price.

Does the operating temperature of drill rigs affect the choice of oil?

Definitely yes - a hard ground drill rig generates a temperature of 65-80°C, while in light duty it is 50-60°C. In warm climates, higher viscosity oils (ISO VG 68) may be needed, and in winter, HVLP oils with a higher VI may be needed for smooth starts.

Does the excavator's hydraulic system directly affect the choice of oil for drill rigs?

Yes - if the excavator has a weaker hydraulic pump (flow less than 40 l/min), it may not be able to drive the drill rigs efficiently, regardless of the choice of oil. Always check the hydraulic parameters of the excavator before installing the drill rigs.