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TRAIL SAVVY: Off-road driving tips, skills, & practices – Breaking in an engine


When you’ve just purchased your new pride and joy, the first thought after unwrapping the ribbon in the dealership could well be along the lines of, “What’s the best way to run-in the engine and transmission to ensure optimum performance and the longest possible service life?”

Older mechanics will probably give detailed schedules of maximum rpm and periods of cooling off for both a new and rebuilt engine. Some of what they say might be true, but this remains a contentious topic with many opinions and no single ‘right way’ to do it. Manufacturers these days make things simple and usually provide a few guidelines – these should be the first thing to check in the User’s Manual.
Put simply, the break-in period is the time a new or rebuilt engine takes for its various bearings, cylinders, ring surfaces, clutches, gears, and other mechanical components to conform to each other’s shape through gradual wear. Despite huge strides in manufacturing accuracy and quality of componentry, microscopic imperfections between binding surfaces still occur. For this reason, any new engine goes through a running-in period despite that all engines are started and tested at the factory.

Cam lobes, bearings, push rods, and the various gears within an engine will bed in on their own accord; the part you need to worry about is the piston, its rings, and the cylinder itself. How you break in these components will affect performance, efficiency, reliability, and oil consumption throughout the life of the vehicle. The first 1 000km of your engine’s life is no doubt the most crucial to its longevity. Small amounts of load must be applied to the engine from cold, warm it up gradually on the road (and under light and varying load) without idling for too long. As temperatures increase, more load can be applied, gradually increasing load to full torque over time as you reach the 1 000km mark.

Since a piston ring is not ‘square’ but instead more of a tapered design, pressure from the combustion chamber forces the ring outwards against the cylinder wall. If load is NOT applied properly during the break-in process the ring and cylinder wall will not wear-in properly against each other, possibly causing glazing of the bore or piston, damage to the cross-hatch patterning on the cylinder bore, and eventual blow-by. These effects will cause your engine to run poorly.

That ‘crosshatch’ pattern is applied to cylinder walls during the manufacturing process to help retain oil against the cylinder walls, where it sits in the microscopic valleys of the patterning, helping retain lubrication and, initially, helping the piston rings seal effectively. If there is a poor seal between the piston rings and cylinder walls, hot gasses may blow by the piston rings and flash-bake the oil on the cylinder, creating a hard deposit layer known as glazing. This will cause high oil and fuel consumption and may cause your vehicle to smoke. To avoid this problem, specially-designed break-in oils are often specified by manufacturers. They are typically replaced with normal specification oils after the first service. In other words, don’t ignore that first service. Interestingly, mineral-based break-in oils are intentionally designed to have a higher friction-co-efficient than the oil your manufacturer recommends using for the life of your vehicle. The higher levels of friction help a new engine bed in faster than it otherwise would with normal oil, making the process much shorter and ultimately extending the life of your engine.

Break-in oils like the Ravenol Break-In SAE20-50 are mineral-based oils with specific additives such as zinc, which help components wear evenly and seat properly when new. After the first service, it’s completely normal to find a small amount of iron filings in the oil filter or magnetic sump plug. These filings should stop appearing after the break-in process, and, if they persist, you may have scored the cylinder linings, damaged your rings, or scored your cam lobes due to incorrect procedure or an engine fault.

As the pistons and rings move past the cylinder wall at great speed under high pressure, a perfect seal is vital to prevent the escape of gasses like unburned fuel blowing past the rings to the crank case, or oil gasses from the crank case reaching the combustion chamber; this is known as ‘blow-by’. A freshly-honed cylinder wall is covered in tiny grooves called cross-hatching that you may not even be able to see with the naked eye. As the rings pass over this rough texture, a fair amount of heat is created just from that friction of the rings running against the cylinder walls. As the rings and cylinder wear down over time to create a perfect seal, a microscopic layer of oil remains trapped in the cross-hatching, providing the necessary surface lubrication. A diesel engine can take as much as 150 hours to properly break in and you may notice significantly improved fuel consumption, refinement, performance, and general ‘feel’ of your engine after an effective break-in.

We canvassed a few experts on their opinion. Freddi Stafford from Ravenol recommends not idling an engine to warm it up while it’s running in; instead, he advises that driving slowly for the first few kilometres to warm up engines, transmission, and other driveline components is a better option. In fact, this should be standard procedure throughout the life of a vehicle. Andrew Kofahl, from Cape town-based diesel injection specialists JEG Diesel, recommends changing your oil after the first 1 000km and not using full throttle and full revs until your vehicle has passed 10 000km. “City driving is good for a new engine due to low loads and a varying RPM range,” he advises. The basic consensus? For the first few thousand kilometres, it’s a good idea to avoid sustained RPM such as occurs with long-distance highway driving or idling for sustained periods. Conversely, overloading your engine or subjecting it to extremely high RPMs from new can also cause damage to the rings, so a cautious approach is always recommended.


Do not – Idle the engine for extended periods during the first few hours of operation as it can cause ‘glazing’ of the cylinder walls, preventing a good seal between it and the piston rings.
Do not – Over-rev or run the engine at more than 70-80% of power capacity for the first 1 000km as this could cause premature wear. Instead, keep the engine at its peak torque RPM, and NOT the invariably much higher peak power RPM.
Do not – Labour the engine by using large throttle openings at very low revs. This puts immense pressure on the crankshaft and causes intense vibrations, which may reduce the life of crank bearings.
Do – Operate the vehicle at peak torque RPMs but not full throttle. The pressure and heat at working RPMS will prevent cylinder glazing and help the rings seat properly into their ring lands.
Do – Despite what many people believe, Ravenol recommends warming up your engine from cold by immediately applying a small load, helping it to warm up faster than it would at idle and preventing cylinder glazing.
Do – After 15 hours of moderate load, you can operate the engine at full capacity but avoid long periods of idling or high revs, always making sure both the coolant and oil is up to temperature before using full throttle.
Do – Adhere to your manufacturer’s recommended service intervals. Do not miss the vital first service. Change oil more frequently if in doubt and using your vehicle in harsh and/or dusty conditions.