Patman
Staff member
I found this question on one of the f-body message boards, and was interested in the answers from you guys.
Question about the temperature of oil
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I would think it's an "ultimate temp", volume/mass and a conduction issue.
I too, have noticed this but have not made any scientific measurements, draw cooling curves, etc.
Temperature at coolest spot on a fully warmed engine:
Coolant = 212°F + under pressure
Oil = 220°F + (what kind of car gets oil the hottest?)
Volume:
Coolant = 10-12+ qts
Oil = 4-5 qts
Location after shutdown:
Coolant = under pressure throughout
Oil = drains down to bottom of pan
The oil with less volume, and not trapped under prssure near hot metal combustion areas will cool quicker - the coolant especially in a water coolant turbo continues to do it's job via convection and conduction even after shutdown.
I too, have noticed this but have not made any scientific measurements, draw cooling curves, etc.
Temperature at coolest spot on a fully warmed engine:
Coolant = 212°F + under pressure
Oil = 220°F + (what kind of car gets oil the hottest?)
Volume:
Coolant = 10-12+ qts
Oil = 4-5 qts
Location after shutdown:
Coolant = under pressure throughout
Oil = drains down to bottom of pan
The oil with less volume, and not trapped under prssure near hot metal combustion areas will cool quicker - the coolant especially in a water coolant turbo continues to do it's job via convection and conduction even after shutdown.
I think a big part of the issue is 'where is the fluid located'? The oil sits in the pan after shutdown, where it's free to cool off independent (mostly) of block temp. OTOH a large amount of coolant is restricted to inside the block, keeping it hot longer, and then too as soon as you start the car and the thermostat opens the hot block begins heating the coolant back up again. Same is true of oil of course, but it heats up more slowly...
R
R
Patman
Staff member
Any more comments?
I thought this topic would generate more interest.
I thought this topic would generate more interest.
MolaKule
Staff member
I think what he's referring to is "thermal lag."
The heat energy input to a mass of material is governed by
the equation: Q = mc(Tf - Ti), where m = mass, c = specific heat, and Tf and Ti are the
temps at the final time and beginning time period.
And heat always travel from the hotter object to the cooler one.
The heat energy input to a mass of material is governed by
the equation: Q = mc(Tf - Ti), where m = mass, c = specific heat, and Tf and Ti are the
temps at the final time and beginning time period.
And heat always travel from the hotter object to the cooler one.
He's measuring oil temp with a pressure gauge? He should get a temp gauge. They're much more accurate
Patman
Staff member
True, it is a lot more accurate, but he drives an LT1 f-body like myself, and I too can basically read my oil temperature from the oil pressure gauge. I can't tell you an exact number mind you, but I can tell when the oil is fully warmed up, since it will read 20psi at idle. When cold, it will read closer to 50psi at idle. So it gives an approximation anyways.
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