Originally Posted by
Old Steve
Caspernz, have a think back at the specification of diesel fuel three decades ago. It had up to 0.3% (3000 ppm) of sulfur in it. When burnt, sulfur created acidic byproducts which the engine oil detergent had to neutralise. In neutralising the acidic combustion byproducts the engine oil's TBN (Total Base Number, or alkalinity reserve) was used up - it was a sacrificial additive.
Nowdays the level of sulfur in diesel is 10 ppm max, so even with less detergent in the oil of a low SAPS engine oil you're going to be able to extend your oil drain period before you need to change the engine oil. Diesel engine oil formulation has modified somewhat over the last 30 years.
I remember back in the 1990s when operators of European trucks thought that they could go to 30,000 to 45,000 km oil drains here in NZ because that was what the truck manufacturer put in their manuals. But they overlooked the conditions that the manufacturer stipulated, that was 30,000 to 45,000 km oil drains if the trucks were operating on light loaded, highway/autobahn conditions running on something like diesel with less than 50 ppm. NZ trucks were operating at higher fuel consumption rates and using much higher sulfur fuel than European trucks, and when we calculated the amount of fuel, and particularly fuel sulfur, being burnt then European trucks should have had 10,000 to 15,000 km oil drains.
If you also think of the oil consumption of say a Cummins NTC350 back in the 1990s, that might have been 2 Litres over a 15,000 oil drain. Multiply that by 4 and you've got 8 Litres over 60,000 km. Oil consumption is largely affected by the operation of another component of the oil, the dispersant. The dispersant's job is to hold contaminants (mainly soot in a diesel engine) in suspension until it can be removed at oil drain. However, the dispersant can only hold a finite amount of soot in suspension, and once that limit is reached then the excess soot will start to deposit and one area it will deposit in is the piston ring grooves. Extremely small deposits in the ring grooves will affect the performance of the oil piston rings and oil consumption will increase towards the end of an oil drain period.
I remember in the BOP in the late 80s, some truck operators contracting for KFL were finding that they checked their oil level every morning and as soon as they had to top up 2 L they'd book their truck in for an oil and filter change. They noticed that their oil analysis results showed oil changes between 14,500 and 15,500 km without exception. That was the range that a good quality diesel engine oil could hold the amount of soot generated before it started to interfere with the operation of the piston rings and oil consumption resulted.
Bookmarks