How do I calculate HTHS if mixing oil????

[Loobed]

I was just wondering.

How do I calculate the HT/HS of an oil mix? If I were to mix (50/50) some synthetic with a 4.0 HTHS with a conventional oil with an HTHS of 3.0? I doubt I would get 3.5 HTHS.

 

[dave1251]

It would be slightly less than 3.5 but close enough for my calculation.

 

[Geonerd]

Mixed viscosity is pretty much proportional to the ratios of the oil multiplied by their viscosity.

Assume 3 quarts of 3.0 and 1 qt of 5.4 gives..

((Q1xV1) + (Q2xV2)) / Total quarts.
(3x3) + (5.4x1) /4
(9 + 5.4) / 4 = 3.6

(Or close enough that it probably doesn't matter.)

 

[salv]

Mixing 2 different oils, or grades does not give you a nice even blend of the 2 oils. They retain their individual properties in the pan and the crankcase.

 

[Coprolite]

Originally Posted By: salv
Mixing 2 different oils, or grades does not give you a nice even blend of the 2 oils. They retain their individual properties in the pan and the crankcase.


You are correct. The individual molecules retain their properties in the pan.

OP, I use the Widman calculator.

 

[Quattro Pete]

Originally Posted By: Coprolite
OP, I use the Widman calculator.

The Widman calculator does not calculate HT/HS. As a matter of fact, HT/HS is not something that can be easily calculated.

 

[Coprolite]

I asked a very similar question in a thread months ago and the consensus was to go to the Widman site and the calculator would be close enough.

I usually use Geonerd's calculation and compare to the Widman.

 

[cp3]

I use the spreadsheet that has been posted for blending, which I believe uses the same or similar calculation to the Wideman site. Using Geonerd's example I came up with 3.5. I am using this on CATERHAM'S recomendation bassed on his research.

 

[Quattro Pete]

Originally Posted By: Coprolite
I asked a very similar question in a thread months ago and the consensus was to go to the Widman site and the calculator would be close enough.

Where on Widman's site does it offer an HTHS calculator? I don't see it.

 

[KCJeep]

Originally Posted By: Quattro Pete
Originally Posted By: Coprolite
I asked a very similar question in a thread months ago and the consensus was to go to the Widman site and the calculator would be close enough.

Where on Widman's site does it offer an HTHS calculator? I don't see it.


It doesn't that I know of. Use the blending viscosity calculator at 100 but insert your HTHS values instead. Close enough for home brewing work.

 

[Coprolite]

For your further reading pleasure:
My old thread

 

[Quattro Pete]

Thanks!

 

[dparm]

Originally Posted By: Coprolite
For your further reading pleasure:
https://bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2584384



Yep. It's not an exact average of the two when doing 50:50, but for all intents and purposes you can do it that way. It has to do with the fact that the viscosity versus temperature relationship is not linear. At very high temperatures (like 150C, where HTHSV is calculated) it is almost entirely linear.

 

[Coprolite]

It is all within the error bars of differences in batches and volume measurement. Using Caterham's experimental data to back up the idea that we should err on the heavy side with the mix as the operational viscosity would be a bit lower than calculated.

For me, the question came up as I had a small amount of 5w20 leftover and wanted to be sure that the resulting mix would still safely be in the 5w30 range.

 

[widman]

I don't go into HTHS calculations, as many have found. But as said, when blending it isn't going to be exact anyway, and since we are not doing critical work, we are close enough with the formulas given and an understanding of density.