Royal Purple Duralec Ultra Diesel 15W40 CK-4 Motor Oil - 5 Gallon

Heavy-Duty Diesel Protection in a 5-Gallon Pail for Demanding Commercial and Fleet Applications

Royal Purple 85561 Duralec Ultra is a fully synthetic SAE 15W-40 heavy-duty diesel engine oil meeting the current API CK-4 service category, making it suitable for use in modern low-emission diesel engines operating under the latest exhaust aftertreatment standards. The Duralec Ultra 15W-40 formulation in the 5-gallon pail format is designed for shop and fleet operations that service diesel trucks, commercial vehicles, and off-highway equipment where bulk purchasing reduces per-unit cost. Royal Purple Synerlec additive technology delivers enhanced film strength at the thin oil films present in modern diesel engine bearing journals, and the full synthetic base stock maintains viscosity stability over extended drain intervals better than conventional or blended alternatives. The API CK-4 rating meets current API CI-4 Plus backward compatibility requirements, making the Royal Purple 85561 suitable for both new engines and older diesel platforms in the same fleet.

Key Features

• Royal Purple 85561 fully synthetic SAE 15W-40 heavy-duty diesel engine oil, 5-gallon pail
• Meets API Service CK-4, backward compatible with CI-4 Plus, CI-4, and CH-4
• Royal Purple Synerlec additive technology for enhanced bearing film strength and wear protection
• Full synthetic base stocks provide improved viscosity stability and extended drain interval capability
• Compatible with diesel particulate filters (DPF), diesel oxidation catalysts (DOC), and selective catalytic reduction (SCR) aftertreatment systems
• SAE 15W-40 multi-grade viscosity for wide operating temperature range in on-highway and off-highway diesel applications
• 5-gallon pail format for fleet, shop, and volume use
• TBN of 10.8 mg KOH/g for robust acid neutralization over the drain interval

Specifications

What's Included

• 1x Royal Purple 85561 Duralec Ultra SAE 15W-40 Diesel Engine Oil, 5-Gallon Pail

Frequently Asked Questions

The Royal Purple 85561 Duralec Ultra meets the current API CK-4 heavy-duty diesel engine oil service category. It is also backward compatible with older API service categories including CI-4 Plus, CI-4, and CH-4, making it suitable for both current-model diesel engines and older diesel equipment in the same fleet without requiring separate oil inventories.

Yes. The Royal Purple 85561 Duralec Ultra CK-4 formulation is compatible with modern diesel aftertreatment systems including diesel particulate filters (DPF), diesel oxidation catalysts (DOC), and selective catalytic reduction (SCR) systems used in EPA-compliant on-highway diesel engines. The CK-4 rating specifically addresses compatibility with low-emission engine designs and their exhaust aftertreatment systems.

API CK-4 is the current heavy-duty diesel engine oil service category introduced to support lower-emission diesel engines with stricter oxidation resistance and shear stability requirements. API CI-4 Plus was the previous top-tier rating. CK-4 oils like the Royal Purple 85561 meet all CI-4 Plus requirements and exceed them in several performance categories, including improved aeration control and better protection against low-speed pre-ignition in newer engine designs.

The Royal Purple 85561 is designed for heavy-duty diesel engines found in Class 6-8 on-highway trucks, medium-duty commercial vehicles, farm and construction equipment, and stationary diesel power equipment. It is suitable for use in Cummins, Detroit Diesel, Caterpillar, Mack, Volvo, and similar platforms operating on standard diesel fuel where a 15W-40 viscosity grade is specified.

The Royal Purple 85561 Duralec Ultra is formulated and rated for diesel engines under API CK-4 and is not specifically rated for natural gas or dual-fuel stationary engine applications, which typically require oils with higher TBN values and specific ash content profiles. For natural gas engine applications, Royal Purple offers separate products formulated to the ASTM D-6987 and API CG-4 natural gas engine oil standards.

The Royal Purple 85561 has a TBN (Total Base Number) of 10.8 mg KOH/g. TBN measures an oil's reserve alkalinity to neutralize acidic combustion byproducts that form in the oil during the drain interval. A higher TBN provides longer-lasting acid protection, which is especially important in diesel engines burning high-sulfur fuel or operating in severe duty cycles where soot and acid accumulation in the oil is accelerated.

Royal Purple Duralec Ultra's full synthetic base stocks and high-performance additive chemistry are engineered to maintain lubricant integrity over extended drain intervals compared to conventional mineral or blended 15W-40 oils. However, actual drain intervals should be determined by an oil analysis program specific to your equipment and operating conditions. Royal Purple recommends following the engine manufacturer's oil change interval guidance when using Duralec Ultra.

Yes. The 5-gallon pail is the standard shop and fleet format for heavy-duty engine oils. The pail can be dispensed using a hand pump or a standard oil transfer pump inserted through the lid opening. A sealed pail maintains oil quality during storage. Once opened, keep the pail tightly sealed between uses and store in a cool, dry environment away from contamination sources.

Installation Instructions

1. Verify the Royal Purple 85561 Duralec Ultra 15W-40 CK-4 meets the viscosity grade and API service requirement specified in your engine manufacturer's service manual.
2. Warm the engine to operating temperature to thin the old oil, then shut it off and allow 5 minutes for hot oil to drain back. Raise the vehicle or equipment as needed and position a drain pan.
3. Remove the oil drain plug and drain the old oil completely. Remove and replace the oil filter with the manufacturer-specified replacement filter.
4. Install a new drain plug sealing washer and reinstall the drain plug, torquing to the manufacturer's specification.
5. Use a pump or pour spout to dispense the required volume of Royal Purple 85561 from the 5-gallon pail into the engine through the oil filler opening. Fill to the engine manufacturer's specified capacity.
6. Reinstall the oil filler cap and start the engine. Verify the oil pressure gauge or warning light confirms normal oil pressure within 10 seconds of startup.
7. Inspect the drain plug and oil filter for leaks. Run the engine at idle for 2-3 minutes and recheck for leaks.
8. Shut off the engine, wait 5 minutes, and verify the oil level is at the full mark on the dipstick or sight glass. Record the service date and odometer or hour meter reading.

WARNING: This product can expose you to chemicals including lead and phthalates, which are known to the State of California to cause cancer and reproductive harm. For more information go to www.P65Warnings.ca.gov.