Viscosity: more or less?

Part two: viscosity that's too low or too high, operating temperatures, clearances in friction pairs, and the eternal “5W-50 or 0W-30” question.

6 articles in the section, about 14 minutes of reading in total

This is the second article about oil viscosity (below is a link to part one). The thing is, car owners have asked a great many questions, both on the site’s forum and by email. And most of these questions come down to the fact that manufacturers often allow several viscosity options, while the opinions of oil sellers, and even of respected mechanics, often run completely counter to the manufacturers’ recommendations.

With all that in mind, I decided to write another article on viscosity, and I hope it will bring a bit more clarity to the question.

Discuss the viscosity articles on the forumPart one: everything you need to know about engine oil viscosity

  1. Too-low oil viscosity you should never use ACEA A1/B1 and ACEA A5/B5 engine oils, or any special oil that lists only a single manufacturer approval, unless those quality classes or approvals are actually listed in your service book or owner's manual… 222 words, 2 min
  2. Too-high oil viscosity if the oil's viscosity is higher than the norm set by the manufacturer, the engine constantly runs at elevated temperatures, which wears its parts out faster… 415 words, 3 min
  3. Oil viscosity at working temperatures how well an engine runs depends not on the absolute viscosity value at a given temperature, but on how that value changes dynamically while running across a given range of working temperatures, and on how well that dynamic matches the design of the specific engine… 469 words, 3 min
  4. Engine warm-up and oil viscosity What actually happens inside an engine when it's cold and the oil's viscosity is several times higher than its calculated working value? Recall your school physics course and the conclusion is clear: if the oil film is thicker than the clearance, friction increases… 204 words, 2 min
  5. What are clearances in friction pairs To start with, a rhetorical question: is the diameter of the piston (assembled with its rings) the same as the inner diameter of the cylinder? Of course not! 342 words, 2 min
  6. 5W-50 or 0W-30? It might seem that everything about the viscosity of engine oils has already been chewed over, but apparently not quite. The questions that keep coming up on… 220 words, 2 min

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