Originally Posted By: bumpasmerc
I would like to learn about two subjects you mention:
- could you give an example of an engine component in it's cold shape, that is particularly vulnerable to wear when the engine oil is cold.
- could you elaborate on activation temperatures for additives. I was not aware that additives needed heat to be activated.
Several owners manuals that I have had advise not allowing the engine to warm up at idle before driving off. They advise just start and go with light throttle. I am wondering if this advise is prompted by mandated fuel mileage targets and environmental concerns rather than what's best for the engine as far as wear is concerned.
Elevated engine speed will warm the oil up faster than sitting idling. I've sugegsted in the past, and my practice is to drive the engine in the 2,000 to 2,500RPM range while I leave town, or the power station site...will be 10C better off at the point that I hit the highway.
So moving off, and driving sensibly warms better than an idle.
While this is predomninantly about breaking in engines...
https://bobistheoilguy.com/forums/ubbthreads.php/topics/4048953/75__of_wear_occurs_at_startup.
Originally Posted By: Shannow
Oft quoted, and used to misinform often, but here's a paper that states it.
https://deepblue.lib.umich.edu/bitstream/handle/2027.42/26638/0000180.pdf
Will try to dig up the other mentioned papers.
Quote:
The cylinder may wear more at TDC than elsewhere [l - 41 but there is measurable wear all over. The piston rings rather than the piston are the main cause of cylinder wear. There is higher wear at TDC than elsewhere because it is the location of the highest contact pressure, the location of the greatest concentration of acids and the location of the thinnest lubricant film. On the latter point, there have been several attempts to calculate [ 5 - 81 and measure [4, 9, lo] the lubricant film thickness between piston rings and cylinder wall.
The film thickness beneath the top compression ring at TDC was found to be very small, in the range 0 - 3.0 pm, because of the low sliding velocity at that location. The maximum oil film thickness was found near the center of the stroke where the maximum speed is reached. This applies, of course, to the condition of normal running. All engines that stop and start do so with very thin lubricant films at all locations. For per- spective on the influence of oil films,
Gumbleton [ll] found that 75% of the total wear which took place during a 2 h run occurred in the first 6 min. Cylinder wear in the progressive stage may occur by several mechanisms but mostly by abrasion and corrosion. Some abrasive wear is caused by par- ticles left in the engine during manufacture and assembly [12]. This is cor- rectible by proper cleaning during the various stages of manufacture [13]. A form of abrasion may result from debris accumulated from various wear mechanisms. However, dust from the intake air or dirt in the lubricating oil probably causes most of the abrasive wear.
Corrosion was found by Williams [14] to be important, particularly under cold-running conditions, i.e. when the products of combustion con- densed on the cylinder walls. The acidic condensate causes high wear rates by corrosion [15 - 171. This mode can be reduced by using thermostats so that engines spend less time running at low temperatures and by the use of acid-buffered lubricants [ 18, 191.
A mechanism of wear by formation and removal of oxides should also be included in the list. This mode of wear is seen in the wear of lubricated steel but it has not been reported to occur in engines. 2.3.
As to additives, things like Zn and MoDTC that form the tribofilms that protect things like camshafts require surface temperatures and contact to break down the molecules and form the required tribofilms. This happens at a much lower rate at low temperatures, and cold, thick oil provides more parts separation, less contact in that very early stage.
(Note: these tribofilms aren't removed completely each start, so don't worry too much about them)
The Industry standard Sequence IVA warmup wear test purposely holds the engine, with fresh cam and lifters at 60 degrees C (give or take), at revs and load to measure the camshaft wear on an engine without that residual protection, and below the point at which the additives fully kick in.
member bobbydavro (oil chemist with one of the majors) confirms that it's the "perfect storm" temperature range. Then they test at a lower temperature (higher viscosity) they get less wear. When they test at a higher temperature (active additives), they get lower wear.
Modern additives (e.g> Castrol Magnatec, and a similar product in Edge) are designed to have a different set of additives that remain through this period.
