Thread: Best oil to use

This is what I've been using for my TD5, can I do better? IMG_2667.jpg

Originally Posted by John_D2

Thanks Rick. Question tho & excuse my ignorance as I'm learning more about engines but I'm not a mechanic (although since buying my D2 last year I'm feeling like a mechanic at times!)

Why is everyone suggesting 10w40 when the manufacturer lists 5w40? I'm in SA

All good John, most mechanics don't understand this stuff.

The reason you can get away with a higher W number is because we don't really need the cold flow characteristics of the 5W.

In most all of Australia except the alpine areas in the depths of winter, most engines would really only need a 15W oil and they'd crank ok, the oil wouldn't be too thick.
And to make it even more confusing I put up some numbers once that showed a 15W-40 Redline oil that was actually thinner at 0* than some 10w, and I think one 5W-40 oil.
It all came down to the way those oils were blended.
Below 0 it all changed pretty quickly.

Without going into too much detail as it can get confusing, the xW number indicates a cold flow pumping pressure range at a certain temperature below 0*C. (not a viscosity range)
The lower the number, the lower the temperature that the oil will pump and not exceed a certain pumping pressure.

The number on the other side of the designation, eg. an xW-30/40/50, etc indicates a viscosity range above 0*.
ie the 30 or 40 or 50 indicates a viscosity range the oil must fall in, it's not a hard and fast number.

The unit for measuring an oil's viscosity is called a centiStoke.
This is called it's kinematic, or measured viscosity and it changes with temperature. (and bear in mind we're talking Newtonian fluids here, fluids that get thinner, their viscosity reduces with increasing temps. Non-Newtonian fluids like some of the silicones become more viscous as they get hotter, and more viscous as they shear)
For example, an SAE40 oil will have a kinematic viscosity somewhere between 12.5cSt and 16.3cSt@100*C, this is the range an xW-40 oil must fall in at 100*C.

[edit] and FWIW I'm using a 5W-40 in the TD5 too. (Penrite Diesel5) It's what Super Crap had, it's what this engine has used previously and I know it works.

This pdf seems to explain it well, (I quickly skimmed through) and it has the pumping pressure and viscosity range charts. https://www.jcmotors.com/images/understanding_motor_oil_viscosity.pdf

This is the Extract from RAVE that lead me top use the 5w40 in my High Compression engine.

I went for xw40 instead of xw30 for the higher temperature range.



oil.JPG

One rule of thumb, do not use an oil that meets ILSAC GF-4 or 5.

These are oils primarily blended for later model engines and part of their design brief is that they enable improved fuel economy.
This is at the expense of the EP protection early style flat tappet engines require.

Originally Posted by rick130

One rule of thumb, do not use an oil that meets ILSAC GF-4 or 5.

Sorry Rick I'm not catching that part.

I think,,,
he means the later spec oils sacrifice engine longevity for better fuel consumption,,

Rick?

Originally Posted by rick130

All good John, most mechanics don't understand this stuff.

The reason you can get away with a higher W number is because we don't really need the cold flow characteristics of the 5W.

In most all of Australia except the alpine areas in the depths of winter, most engines would really only need a 15W oil and they'd crank ok, the oil wouldn't be too thick.

I disagree with you on this part Rick.

90% of engine damage is done in the first minute.
0W oil provides the best cranking viscosity.


so if your engine is designed for a viscosity of 10.
at 24 degrees
0W has a viscosity of 40
10W has a viscosity 100

neither of the them provides enough protection, but 0W is a lot closer then 10W!

Penrite tech advice to me today