Thread: Oil Viscosity Comparison

Whats the difference between Auto Transmission Fluid and Transmission oils?.I ran ATF for 400K(transmax M) in my R380 and MTF(Redline MTL) for the last 100K.I changed because the ATF was grating in really hot,40C temps were's MTL has been fine up to 50C,the hottest I've measured it in. Pat

Originally Posted by PAT303

Whats the difference between Auto Transmission Fluid and Transmission oils?.I ran ATF for 400K(transmax M) in my R380 and MTF(Redline MTL) for the last 100K.I changed because the ATF was grating in really hot,40C temps were's MTL has been fine up to 50C,the hottest I've measured it in. Pat

ATF is a bit lower in viscosity than the (other) transmission fluids. When I get a minute I will add it to the graph. The slightly increased viscosity plus better additive package in the MTF type fluids are why they work better at high temps.

I was most surprised that 15W40 engine oil is slightly more viscous than EP90.

Can't remember whether I saw this here, or elsewhere, but I found this interesting.
Shows viscosity differences between various oil weights at low temperature

http://i.imgur.com/ZK5VcgM.mp4

I was most surprised that 15W40 engine oil is slightly more viscous than EP90.[/QUOTE]



Very interesting, thanks for that. Can someone explain in simple terms, how the engine oil can be more viscous when it appears to be so much 'thinner' than EP90? To a layman like me?? Does it hold it's consistency at temperature, better than the 90 does? Cheers.

Originally Posted by Gordie

Can someone explain in simple terms, how the engine oil can be more viscous when it appears to be so much 'thinner' than EP90? To a layman like me?? Does it hold it's consistency at temperature, better than the 90 does? Cheers.

I am not sure engine oil appears "thinner" - it is just that you probably have never tested them side by side on a viscometer, or maybe you are confusing density and viscosity.

The rating numbers / system used for engine oil are different than for gear oil.

E.g. if you compare Castrol mineral EP80W90 vs Castrol RX super 15W40, the pour point of 15W40 is -33*C, whereas the EP90 is -35*C, so right across the full temperature range it is slightly less viscous (i.e. thinner).

Originally Posted by isuzurover

I am not sure engine oil appears "thinner" - it is just that you probably have never tested them side by side on a viscometer, or maybe you are confusing density and viscosity.

The rating numbers / system used for engine oil are different than for gear oil.

E.g. if you compare Castrol mineral EP80W90 vs Castrol RX super 15W40, the pour point of 15W40 is -33*C, whereas the EP90 is -35*C, so right across the full temperature range it is slightly less viscous (i.e. thinner).

Thanks mate, that does clear it up a bit for me, I think I might have had the density confused with the viscosity.

I found the Penrite Light Gear Oil to be too thick in my LT77, making gear changes very baulky.

When I compared Penrite Oils data sheets, I found that the Synthetic ATF was a lot more stable at higher temps than the Light Gear Oil; so used that for a long time in my R380.

After decades of Penrite use, I have now found the Nulon Light Gear Oil to work really well on the R380. More viscous than the Penrite ATF, without the selection issues of the Penrite Light Gear Oil.

I'm trying to decide which way to go as my R380 will hit 500,000km's in a month or two so needs a flush and change.I'd like to stay with MTL but a lot more choices are around now. Pat