GL-5 Gear Guard

Heavy-duty gear oil for extreme-pressure wear protection.

Commercial vehicle transmission fluids serve manual gearboxes, drive axles (differentials) and hydraulic or hydrodynamic systems in trucks, buses and construction machinery. Hypoid gears in drive axles combine sliding and rolling contact under high pressure, which is why extreme-pressure additives are used to resist scoring and pitting.

This page covers GL-5 Gear Guard (Heavy Duty Vehicle Gear Oil) — product code GL-5; category Automotive Lubricants / Commercial Vehicle Oils / Transmission Fluids; SAE 75W-90 / 85W-140; GL-5; pack 18L. The specification table below is taken from our product data as recorded, with no values estimated or filled in.

The table below reproduces the recorded product data; the notes that follow explain the classification and viscosity systems in general terms.

• SAE 75W-90 —— A gear-oil viscosity grade per SAE J306 — a different scale from engine oils (SAE J300), so the numbers are not interchangeable: the number before the W is the low-temperature grade, the number after it is the high-temperature viscosity grade.A common gear-oil grade combining low-temperature flow with high-temperature protection.
• SAE 85W-140 —— A gear-oil viscosity grade per SAE J306 — a different scale from engine oils (SAE J300), so the numbers are not interchangeable: the number before the W is the low-temperature grade, the number after it is the high-temperature viscosity grade.A thicker gear-oil grade, typically used in heavily loaded drive axles and demanding gear applications.
• API GL-5 is a gear-oil specification for hypoid gears and other high-load, shock-loaded gear sets; its sulphur-phosphorus EP additive level means it is generally not recommended for manual gearboxes with brass or bronze synchronisers.
• 18L：Workshop and fleet size, suited to servicing several vehicles or a single commercial fill.
• Grades and viscosities are stated on the product label and pack; the values listed here are exactly as recorded in our product data, and further technical documentation can be requested from our sales team.

This range contains 2 recorded variants (viscosity grade × packaging), listed below. The images in the gallery correspond to these variants and can be switched to inspect each pack.

• Forms an extreme-pressure film under high contact pressure to resist scoring, pitting and scuffing.
• Reduces friction and temperature rise in gears and bearings, improving transmission efficiency.
• Resists oxidation and thermal ageing to support longer drain intervals.
• Carries heat away and provides rust and corrosion protection in wet or heavily loaded service.
• In synchronised gearboxes it must also satisfy shift-feel friction requirements (such applications use a matching GL-4 or dedicated manual transmission fluid).

• Drive axles (differentials) of heavy trucks.
• Manual gearboxes, where synchronised units take a matching GL-4 or dedicated manual transmission fluid.
• Gearboxes and drive axles on construction machinery.
• Hydrodynamic and hydraulic systems on commercial vehicles.

Gear oils such as GL-5 rely on sulphur-phosphorus EP additives and are generally not suitable for manual gearboxes with brass or bronze synchronisers, while hydraulic fluids are specified for viscosity-temperature behaviour, air release and filterability rather than extreme-pressure capacity. The three fluid types are not interchangeable.

• Follow the viscosity and performance grade specified in the vehicle or equipment manual; when several options are listed, choose according to ambient temperature and actual duty cycle.
• Manual gearboxes must use the specified fluid: gearboxes with brass or bronze synchronisers normally call for GL-4 or a dedicated manual transmission fluid rather than GL-5.
• Avoid long-term mixing of different brands or performance levels; prefer the same specification when topping up or changing fluid.
• Under sustained heavy load, frequent stop-start, hot or dusty conditions, shorten the drain interval and check fluid condition regularly.
• Replace filters where applicable during a fluid change and check the level and any leaks as specified.

• Product name and code: distinguishes different series built to the same specification (the recorded code is listed in the table above).
• Viscosity grade (SAE), e.g. 5W-30: rates low-temperature flow and high-temperature viscosity.
• Performance grade, e.g. API SP or ACEA A3/B4: the standard system and level the fluid meets.
• Net content and pack form, e.g. 4L or 18L: match it against the fill volume you need.
• Batch number and production date: for traceability and shelf-life checks.
• Manufacturer information and contact details: the reference point for any follow-up questions.

• Drain while the fluid is still warm for a more complete change, and have both a drain pan and a used-oil container ready.
• Replace the filter where applicable as the manual requires, and check that the sealing ring is intact.
• Use clean funnels and tools so that moisture, dust and debris do not enter the system.
• Fill to the volume the manual specifies and confirm the level on the dipstick or sight glass; transmission fluids usually need to be checked at a specified fluid temperature and by a set procedure.
• After the change, check the drain plug and mating surfaces for leaks, then re-check the level after a short run.
• Record the mileage or operating hours and the date so the next service can be scheduled.

• "Thicker is safer": only true within the range the manual allows — a viscosity that is too high raises flow resistance and can starve the engine during cold starts.
• "Dark oil means dead oil": diesel engine oil normally darkens as it disperses soot; decide on changes by mileage or hours and by oil analysis rather than colour.
• "The same grade from any brand can be mixed freely": emergency top-ups are understandable, but long-term mixing risks incompatible additive systems and can affect cleanliness and seals.
• "More oil is better": overfilling raises crankcase pressure and loads the oil separation system; fill to the dipstick mark.
• "A higher category always suits my engine": also check viscosity and the manufacturer approvals the manual calls for — some engines set specific limits on ash and phosphorus.

• Store in a cool, dry place away from direct sunlight and rain.
• Keep containers sealed against moisture, dust and contaminants, and use opened packs promptly.
• Keep production batch numbers on record and use stock on a first-in, first-out basis.
• Dispose of used oil and empty containers in line with local regulations to avoid soil and water contamination.

• Selection support: tell us the vehicle or equipment model, ambient temperature and duty cycle in your enquiry and we will point to the specifications we actually offer.
• Technical documentation: for more detailed product information, packaging or bulk supply, contact the sales team through the enquiry form and we will answer with what we have on file.
• Pack choice: the same specification often comes in several pack sizes — pick according to fill volume and stock turnover.
• Samples and volume: for bulk or long-term supply, include the quantity and delivery location in your enquiry.