Oil Level Checking (Again!)

[jl-c]

OK, I am prepared to be shot down, however having followed this after an oil change it works for me. I used the maths below to work out how much the oil would expand when hot as against cold. Did the oil change ran the engine for a minute to get the filter full and the pressure up, then let it stand until the time reverted to the 6 second checks. Topped up oil cold until the last segment was not illuminated. When the car/oil is run up to temperature and then the oil is checked it gives a full indication.

 

Specific volume of a unit can be expressed as

The change in the units volume when temperature change can be expressed as

 

dV = V₀ β (t₁ - t₀)          (2)

v = 1 / ρ = V / m         (1)

where

v = specific volume (m³/kg)

ρ = density (kg/m³)

V = volume of unit (m³)

m = mass of unit (kg)

 

The density of a fluid when the temperature is changed can be expressed as

where

 

dV = V₁ - V₀ = change in volume (m³)

β = volumetric temperature expansion coefficient (m³/m^{3 o}C)

t₁ = final temperature (^oC)

t₀ = initial temperature (^oC)

 

ρ₁ = m / V₀ (1 + β (t₁ - t₀))

 

    = ρ₀ / (1 + β (t₁ - t₀))          (3)

where

ρ₁ = final density (kg/m³)

ρ₀ = initial density (kg/m³)

 

 

Volumetric Temperature Coefficients - β - of some common Fluids

• water : 0.000214 (1/^oC), 
• ethyl alcohol : 0.00109 (1/ ^oC), 0.00061 (1/^oF)
• oil : 0.00070 (1/^oC), 0.00039 (1/^oF)

 

OK, tin helmet on, awaiting flak  :eek:

[Ahsai]

Very simple. All you need is the last line - oil expands 0.00039 per degree.

 

Hot engine ~220F and room temp ~75F and that's 145F temp difference. The oil volume expansion is then 0.00039 * 145 = 5.6%

5.6% of 9L of oil = 0.5L