Interesting Oil Facts #2
 

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

So why don't manufacturers limit rpm by oil temperature/viscosity ?

DunxC

Easier to specify the correct oil I would say

Cheers

But what your saying is that at my "normal" 80 degrees I shouldn't be using high revs ?

DunxC

bttt, as above so at 80c 10/50 oil should not be used at high rpm:wonder: if so i'm in trouble as i wait to see 80odd before pressing on a bit:confused:

Yes same as above, i stay off boost untill i see 80c before i open her up and take it round into the red

bttt for an answer please:thumb:

I don't think a road car is going to suffer from centistoke-itis myself...

I expect to blow mine up in the next two years, if the clutch lasts that long

LOL

DunxC

80degC is an acceptable temp for pushing the loud pedal, I would not do it at 40degC though.

If your car never sees 80degC then a 5w-40 or 10w-40 would be better than a 10w-50 or 15w-50

Cheers

What about oil temps between 80degc upto 110degc?

Higher is better... too high isn't

LOL

DunxC

P.S. 110 plus and I would fit a cooler...

I have a oil filter mounted cooler allready.

What temps should i stay away from, 110+ if using 10 40 ??