Basic knowledge of automotive lubricants: Analysis of the role and core functions of engine oil

Engine oil is known as the "blood" of the engine and is the key to ensuring the healthy operation of the car's heart (engine). But many car owners' understanding of engine oil is limited to "regular replacement", without knowing the scientific principles behind it. This article will systematically analyze the six core functions of engine oil and reveal how high-quality engine oil can extend engine life by more than 100000 kilometers.

1、 The core function of engine oil

1. Lubrication and friction reduction (the core of the core)

Working principle: Form an oil film (approximately 0.001-0.1mm thickness) between metal components

Key data:

Reduce friction coefficient by 60-70%

Reduce engine wear by over 80%

Typical scenario:

Lubrication of piston rings and cylinder walls during cold start

Sliding friction between camshaft and valve tappet

2. Clean and disperse

Combat objects: carbon deposits, sludge, metal debris

Cleaning mechanism:

Dispersant wraps pollutants (each drop of engine oil contains millions of cleaning molecules)

Alkaline additives neutralize acidic substances

Effect comparison:

Oil type

Cleaning capacity (sediment volume per 10000 kilometers)

Mineral oil 350g

Total synthesis 50g

3. Cooling and temperature reduction

Data comparison:

Engine oil takes away heat: about 6-10% of the total heat generated

Piston top temperature: can reach 600 ° C without oil cooling → drops to 300 ° C with oil cooling

4. Sealed and leak proof

Sealing part:

Piston rings and cylinder walls

Valve guide

Sealing principle:

Appropriate viscosity forms an oil film seal

Typical data: Increase cylinder pressure by 15-20%

5. Rust and corrosion prevention

Protection mechanism:

Rust inhibitor forms a protective film on the metal surface

Alkaline reserve value (TBN) neutralizes acidic substances

Key indicators:

High quality engine oil TBN ≥ 7

Poor quality engine oil TBN ≤ 3

6. Shock absorption and buffering

Location of action:

Crankshaft bearing

rod bearings

Buffer effect:

Reduce impact noise by 30-50%

Extend bearing life by 2-3 times

2、 Composition Science of Engine Oil

1. Base oil (accounting for 70-90%)

type

Production process

Performance characteristics

Representative brand

Mineral oil physical distillation has low cost and average performance compared to the Great Wall Gold Star

Semi synthetic mineral oil+hydrogen cracking with high cost-effectiveness Shell HX7

Fully synthetic chemical synthesis (PAO/esters) resistant to high and low temperatures, long-lasting Mobil 1

2. Additives (accounting for 10-30%)

Cleaning agent: Sulfonic acid salt/phenolic salt (anti sludge)

Antiwear agent: ZDDP (Zinc Dialkyldithiophosphate)

Viscosity index improver: OCP (olefin copolymer)

Pour point depressant: Alkyl naphthalene (improves low-temperature fluidity)

3、 Key indicators of engine oil performance

1. Kinematic viscosity (cSt)

100 ° C test value:

20: Japanese New Car

30: Most household cars

40: German turbocharged cars

2. Viscosity index (VI)

Mineral oil: about 100

Total synthesis: up to 200+

3. Flash point (° C)

High quality engine oil: ≥ 230 ° C

Poor quality engine oil: ≤ 200 ° C

4. Tilt point (° C)

0W engine oil: ≤ -45 ° C

10W engine oil: ≤ -30 ° C

4、 The Golden Rule for Oil Selection

1. New car selection

Priority 0W-20/5W-30 low viscosity total synthesis

Example:

Toyota: 0W-16

Volkswagen: 0W-20 (508 standard)

2. Old cars over 100000 kilometers

Appropriately increase viscosity:

Original 5W-30 → switched to 5W-40

Reason: Increased engine clearance

3. Adaptation to extreme weather conditions

ambient temperature

Recommended label

-0W-20/0W-30 below 30 ° C

Resident at 35 ° C+5W-40/10W-40

5、 Common cognitive misconceptions

❌  Misconception 1: "The more expensive the engine oil, the better"

✅  Truth: Matching engine design is key

❌  Misconception 2: "Full synthesis must be replaced after 10000 kilometers"

✅  Truth: Long acting fully synthetic can reach 20000 kilometers

❌  Misconception 3: "If the engine oil turns black, it needs to be changed"

✅  Truth: The cleaning function of modern engine oil can quickly darken the oil color