CLB
Well-Known Member
..... if I mix 2 litres of 20W50 with 2 litres of 10w40, do I now have 4 litres of 15w45.
Not actually planning on doing this, just idle curiosity.
Not actually planning on doing this, just idle curiosity.
Hypothetical oil question.......
- Thread starter CLB
- Start date
RichardS
N/A
The simple answer is no, you don't.
You are likely to end up with something between the two extremes but it won't be a simple average.
Richard
You are likely to end up with something between the two extremes but it won't be a simple average.
Richard
lw395
Well-Known Member
I'd say you'd have 4 litres of dubious oil.
If you need it to do more than 20w40, I wouldn't go there.
I've heard of people blending motorcycle fork oil to get a particular viscosity, it seems to be be a Dark Art.
If you need it to do more than 20w40, I wouldn't go there.
I've heard of people blending motorcycle fork oil to get a particular viscosity, it seems to be be a Dark Art.
VicS
Well-Known Member
No because AFAIK there is no defined viscosity range for SAE 45. You will end up with an oil with high temperature characteristics that fall within the SAE 40 range or SAE 50 range.
You might end up with an oil with low temperature characteristics corresponding to SAE 15W but at best it will either be 15W40 or 15W50
zambant
Well-Known Member
No
sarabande
Well-Known Member
What a shame ! I have this urgent need for an oil listed as 17W36, and was looking forward to some fun mathematical mixing.
lw395
Well-Known Member
CLB
Well-Known Member
Care to elaborate? I repeat, I have no desire or need to do this, I just cant understand why the numbers would not average out if mixed equally. Forget the fact that there is no standard for 45, would it 'in theory' be a 15w45?
If there is something in the makeup of the oil that would stop them mixing, that would be a good reason to suggest the answer is NO, but if they mix well, what else is at play?
A few people have said no, but no one seems to want to explain why. VicS came nearest to suggesting it might, in fact, be something that COULD be 15w45 or thereabouts.
vyv_cox
Well-Known Member
The two oils will mix together, this is a condition of the specification and all manufacturers test for it. The final viscosity is not straightforward. The first figure in the viscosity expression is that of the base oil, so mixing a 20 and 10 weight oil in equal proportions might well result in 15. The second, high temperature figure is achieved by Viscosity Index improvers, clever molecules that straighten out as the temperature increases. I have no knowledge whether the same VI improvers are used for all grades and manufacturers certainly do not all use the same package, so there could be wide variation on mixing.
RichardS
N/A
Indeed so. It's also the case that the high temperature viscosity covers a range of viscosity and you can get a 30 oil and a 40 oil which are relatively close to each other in viscosity or at opposite ends of the scale. When you mix them you might end up with something which is in the middle or something which still actually tips over into either the higher or the lower band.
Provided both oils are within the range that is acceptable, then mixing is fine but if one oil was within the acceptable range and the other was outside it, you might end up with a mixture which is outside. That can only be determined by actually measuring the viscosity and seeing which grade it falls into.
Richard
Spirit (of Glenans)
Well-Known Member
I used to have an airless spraygun for which there was an accessory called a 'viscosity cup', basically a cup with a cone-shaped bottom with a hole in it. The viscosity of the paint mixture could be measured by observing the time it took for the cup to empty. No doubt something similar could be rigged up to discover, by comparison and adjustment of the mixture, the viscosity of your hypothetical blend at the relevant temperatures.
