The proper way to change oil.

[megaladon6]

actually the better question to ask is; if it gets thicker, why does the pressure drop? like i said there is a difference between the lab tests and the real world.

 

[kingcolbert83]

the first number is the viscosity (thickness) of the oil when the engine is cold. Once the engine gets to operating temps the second number is the viscosity (thickness). The w stands for winter. The lower the number the less viscosity (thickness of the oil). So a 5w30 will start out thin at a 5 weight and heat up to a 30 weight. A 10w40 will start out at a 10 weight and heat into a 40 weight>

If you have a older motor with high mileage and a few oil leaks it is better to use a higher viscosity oil.

 

[GP403]

http://www.valvoline.com/carcare/articl ... section=hm

 

[HFX]

I run nothing but 30 weight in my engine pretty much all the time. Living in the south it rarely gets cold enough to worry about needing lighter weights.

 

[srercrcr]

Thank you GP403.
I read..... the higher the temperature, the lower the viscosity (thickness), the oil thins out. VERSUS "thicker when it's hot: from KingColbert. Is this an attempt at revisionist mechanics?

 

[GP403]

I think the thing everyone's forgetting is pressure. Under no pressure (i.e. in your pan) hot oil is thinner/flows easier, sure. Under pressure though is when the visc. kicks up, so yes it is thicker hot AND under pressure, under normal conditions in your engine. At least that's what I take away from that. Been way too long since I took Fluid Mechanics 101, though 😀

 

[Derision]

I think the thing everyone's forgetting is pressure. Under no pressure (i.e. in your pan) hot oil is thinner/flows easier, sure. Under pressure though is when the visc. kicks up, so yes it is thicker hot AND under pressure, under normal conditions in your engine. At least that's what I take away from that. Been way too long since I took Fluid Mechanics 101, though 😀

To my understanding, the fact that it's also under pressure whilst in a running engine mucks about with things.

Wow... and I was just kind of making that up.

I feel so awesomely smart right now.

 

[pontiacgp]

I think the thing everyone's forgetting is pressure. Under no pressure (i.e. in your pan) hot oil is thinner/flows easier, sure. Under pressure though is when the visc. kicks up, so yes it is thicker hot AND under pressure, under normal conditions in your engine. At least that's what I take away from that. Been way too long since I took Fluid Mechanics 101, though 😀

it's all relative....the oil under pressure may be thicker than the oil in the pan but the oil under pressure is thinner than the oil under pressure when it was cold.....my oil pressure drops from 80 cold to 50-60 under operating temps...although the 80 is a higher pressure because the oil is thicker I am getting less oil distributed and if that condition persisted it would increase the engine temp...the oil thins as it is heated giving me lower pressure but higher volume....