Video summary

Why Some Engines Burn Oil and Others Don't

Main summary

Key takeaways

Educational

Main ideas about why some engines burn (consume) oil

The video explains oil consumption as a complex issue with no single fix. It argues that different engines fail in different ways, and actions that help one engine can worsen another, depending on factors like seal condition, PCV design, ring tension, and operating conditions.

Three key causes of oil consumption

1) Seals (external leakage + oil entering intake/exhaust)

Engines rely on multiple seals where oil can escape, including:

  • Rear main seals
  • Valve stem seals
  • Turbocharger seals

Failure modes

  • Rear main seal leak → oil leaks externally (often visible as drips/droplets). Still counts as consumption.

  • Valve stem seal leak or turbocharger seal leak → oil enters the intake or exhaust, leading to smoking and potential engine damage.

How modern oil relates to seals

  • The API (American Petroleum Institute) tests motor oils for seal compatibility, including interactions with seal materials.
  • Pre-2000 engines may use different seal materials (including older rope seals) and may require higher-viscosity conventional oil that matches those materials.
  • 2000+ engines generally benefit from API-tested compatibility, making conventional and synthetic oils compatible with typical seal materials.

Aging effect and high-mileage oils

  • Seals can harden with age.
  • High mileage oils may include additives (e.g., esters / seal conditioners) to help reduce leaks.

2) PCV valves / crankcase ventilation (sucking oil vapor into intake)

Core concept

  • Piston rings are imperfect, so some blow-by gases enter the crankcase.
  • Without proper venting, crankcase pressure builds and can damage seals.

Modern vs old PCV approach

  • Old engines may vent crankcase gases directly to the atmosphere.
  • Modern engines use a PCV valve to regulate crankcase pressure and route vapors into the intake/manifold using intake vacuum.

When PCV fails, two harmful scenarios can occur

  1. Clogged/damaged PCV valve (can’t relieve pressure)
    • Pressure builds → can blow out seals → more oil leaks/consumption.
  2. PCV valve stuck open (too much flow during high vacuum)
    • During throttle closure, intake vacuum increases.
    • If PCV can’t regulate flow, it can pull excess oil vapor from the crankcase into the intake.

Example: LS engine “notorious oil consumption”

  • The PCV routing allowed oil vapor to be pulled effectively into the intake stream (“suck oil straight from the crank case”).
  • A secondary contributor is windage/oil mist generation:
    • Oil drainage and crankshaft splash create mist/vapor
    • Vapor condenses in the cooler intake manifold area

Fuel system interaction (port vs direct injection)

  • Port injected engines: fuel can wash/cool and contains detergents, helping mitigate intake valve deposits from PCV oil vapor.
  • Direct injection engines: less/no fuel washing upstream of intake valves → deposits can accumulate more.

Manufacturer design response

  • Many modern systems use dual injection (direct injection + port injection):
    • Port injection helps clean intake valves because detergent-containing fuel reaches deposits where they form.

Oil volatility and PCV/oil vapor

  • Higher oil volatility → more likely to become vapor and be pulled through PCV.

Volatility testing nuance:

  • NOACK test (250°C for 1 hour) historically correlated with oil consumption for some oils/grades.
  • For newer low-viscosity oils (e.g., 0W-8), correlation may be weaker.
  • JASO alternative: 150°C for 12 hours → potentially better correlation with real-world use for modern oils.

3) Piston rings (sealing and oil scraping ability)

Two ring functions

  1. Gas pressure sealing
  2. Ring tension / scraping oil (removing oil from cylinder walls)

Low-tension rings and tradeoffs

  • Fuel-efficient engines use low-tension piston rings to reduce friction.
  • Tradeoff: potentially reduced oil scraping capability.

Example tension loss mechanisms

  • Second ring design (Napier-style oil control ring with a hook):
    • New hook is sharp and scrapes effectively.
    • As mileage increases, the hook wears → scraping ability declines.
  • Detonation impacts ring performance:
    • Detonation can lower/alter effective ring tension and disrupt oil control.
    • With low-tension rings, detonation can worsen oil control.
  • Spring fatigue in ring packs:
    • Oil control ring sets use spring/expander force (2-piece: spring behind outer ring; 3-piece: expander acts as spring).
    • Over time, springs can fatigue, and detonation can weaken them further.

Ring groove deposits

  • Deposits in piston ring grooves can stop rings from moving freely.
  • That reduces effective ring tension and scraping performance → increasing oil consumption.
  • The video references a product/research context as an example of cleaning ring grooves.

Consumer-oriented mitigation steps (chemical + mechanical)

A) Keep the engine clean (chemical/maintenance-focused)

Goal: reduce deposits that worsen oil control and increase oil-vapor-related problems.

Two cleanliness targets:

  1. Fuel injectors
    • Dirty injectors → poor fuel atomization → more fuel dilution in oil.
    • More fuel in oil → more volatility → more oil vapor through PCV → more deposits → more oil consumption.
    • Action: keep fuel injectors clean.
  2. Piston ring grooves
    • Suggested approach:
      • Use top-tier fuel (stronger detergent package).
      • Use a high-quality oil with stronger cleanliness characteristics.

Oil “quality” nuance:

  • API approval ensures minimum requirements, but doesn’t guarantee top cleanliness.
  • The video cites examples of oils it considers better for ring-groove cleanliness (named brands/formulations).
  • It also suggests engine manufacturers have had quality issues recently (e.g., recalls), implying cleanliness/control may be harder in modern engines.

B) Choose viscosity carefully (don’t assume thicker oil fixes everything)

  • Putting in higher viscosity oil can increase oil consumption if piston ring tension is already low.
  • Viscosity can help or hurt depending on the engine’s dominant issue:
    • Older seals (e.g., rope seal type) might benefit from higher viscosity to reduce seal leakage.
    • Low-tension rings might experience worse oil control with higher viscosity.
  • Bottom line: there is no one-size-fits-all chemical or viscosity solution.

C) Mechanical / operational steps

  • Ensure the PCV system works properly
    • Clean/replace the PCV valve if needed.
  • Driving style and engine cycling matter
    • Higher sustained RPM and more engine cycles can increase oil consumption.

Example comparison:

  • Lower RPM cruise (e.g., ~50 mph at ~2000 RPM) → less oil consumption

  • Higher RPM cruise (e.g., ~75 mph at ~3000 RPM) → more oil consumption

  • Don’t overfill the oil

    • Excess oil increases windage (aeration/mist generation) → more oil vapor → more load on PCV and potentially more consumption.

Oil consumption “normal vs abnormal” guidance (quantitative)

Rough benchmarks from the video:

  • < 1 quart per 3,000–5,000 miles → “really good”
  • ~ 1 quart per 2,000–3,000 miles → “pretty normal”
  • > 1 quart per < 1,000 miles → “abnormal”

Speakers / sources featured

Speaker / presenter

  • Lake — “the motor oil geek” (host of the video)

Organizations / sources mentioned

  • Ford (referenced via a class action lawsuit related to oil consumption)
  • API (American Petroleum Institute) (seal compatibility testing and oil spec testing)
  • JASO (Japanese Automotive Standards Organization) (proposed NOACK alternative volatility test)

Engine/platform examples mentioned

  • Porsche (flat engine example)
  • Subaru (flat engine example)
  • LS engines (notorious oil consumption example)
  • LT direct injection engines (dual-fuel / DI vs port injection contrast)
  • GM Dexos spec (NOACK one-shot lab requirement mentioned)
  • Porsche Boxster (flat engine with integrated air-oil separator mentioned)

Named oil/product brands mentioned (as examples)

  • Valvoline (Restore and Protect referenced)
  • Penso Ultra Platinum
  • Mobil 1 Extended Performance (with “alkalated napalene” mentioned)

Original video