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Oil pressure

7.1K views 10 replies 8 participants last post by  MickRS  
#1 ·
Forgive me for being a mechanical noob but the oil pressure gauge. 3rd along on the middle display. Is it supposed to move up and down as you accelerate? Only noticed mine today and it rises and drops as I drive. Should this be a constant steady value or move around?
 
#7 ·
Great. Just trying to understand all the readings mechanically! :)
When the oil is cold it is thicker and this results in higher pressure. As it warms it becomes thinner so the pressure drops.

As the revs increase the oil is pumped faster around the engine making the pressure rise, at idle the pressure is therfore lower.

A combination of both of the above leads to the readings you see :)
 
#9 · (Edited by Moderator)
When the oil is cold it is thicker and this results in higher pressure. As it warms it becomes thinner so the pressure drops.

As the revs increase the oil is pumped faster around the engine making the pressure rise, at idle the pressure is therfore lower.

A combination of both of the above leads to the readings you see :)
If I remember my Physics, isn't it Boyle's Law? I think it's PV = k, where Pressure x Volume equals a constant. Scraping the little grey cells, but the constant (k) is also related to temperature. So as the temperature of the Oil increases, it becomes less dense and so occupies less volume, resulting in higher pressure (???). The same principle as a hot air baloon. As I say, I may be wrong on some of the details. It's been 30 years since I studied this at school :blush:
 
#10 ·
If I remember my Physics, isn't it Boyle's Law? I think it's PV = k, where Pressure x Volume equals a constant. Scraping the little grey cells, but the constant (k) is also related to temperature. So as the temperature of the Oil increases, it becomes less dense and so occupies less volume, resulting in higher pressure (???). The same principle as a hot air baloon. As I say, I may be wrong on some of the details. It's been 30 years since I studied this at school :blush:
Nah, Boyle's law is a gas law.

It's all fluid dynamics and Mr Newton had quite a bit to say... It all gets a bit messy.