Interesting Oil Facts #2

[oilman]

At which temperature does an oil flow better?

There is no temperature where oil suddenly starts to flow better.

A 10W/40 for example will flow between -25C and 100C or more, but there is some difference in the rate of flow! (True viscosity at -25C is about 7000 Centistoke(cSt) units, dropping to 14 at 100C. ‘Viscosity’ is really just another name for ‘rate of flow’.)

The correct question is at what (sump) temperature is an oil at a viscosity that suits a modern high-RPM engine? Present day designs are happy on an oil viscosity of 10 to 15 cSt. (But many are OK on less than 10.) 30cSt is too high at high RPM. It can lead to foaming, air entrainment and cavitation.

Temp. for 30cSt (DegC)..........Temp. for 15cSt ............Temp. for 10cSt

5W/40.........71.............................90...... ...........................117

10W/40.......70.............................99........ .........................118

10W/50.......80............................109........ ........................130

10W/60.......89............................119........ ........................142


As you will see from the above table a 5W/40 or a 10W/40 is perfectly adequate for all engines except those that run unusually high temperatures (120degC plus)

Cheers
The Opie Oils Team

[iced_to_the_max]

should my oil pressure go up and down as i am driving??? sits about 4kg/cm2 when driving quite hard then drops to about 1 when at traffic lights

[oilman]

Yep, thats normall the pressure increases with revvs.

Cheers

Guy.

[Rich B]

now we're in to these cold mornings...

is it correct to think a 10w/50 will offer less protection while the engine gets up to operating temp than a 10w/40 or 5w/40?

[oilman]

Cold start perrformance is no different to 10w-40 however 5w will flow quicker from cold.

Cheers

Guy

[Kez]

I use 15/50 and its like glue!!