Does the HT/HS go up when Mixing?

Southern NJ
We know mixing M1 is fine, due to the similar chemistry. But how does this work on a molecular level? Patman had a good point here:
One thing that has me curious is that if you mix two oils, how does it affect the HTHS? I wonder if it becomes an average of the two, or if it leans more towards the lower side? For instance, if you mix in Mobil 1 5w30 (with it's 3.08 HTHS) and Mobil 1 15w50 (with it's 5.11 HTHS), in an exact 50/50 ratio, will the resulting HTHS number then become 4.1? We know the viscosities might not behave exactly like this, due to different levels of VII in each oil, however the resulting viscosity should be pretty close to 91cst at 40c, and 13.7 cst at 100c, give or take a few %. So in effect you'd have something close to a 10w40 to 15w40 oil probably.
[ August 30, 2003, 07:02 PM: Message edited by: buster ]


Staff member
Iowegia - USA
Let's say you're mixing Mobil 1 SS 5W30 of HTHS of 3.0 with a 15W50 such as M1 SS of 5.X, then yes, the HTHS will go up, but only slightly, say to 3.5 or so. Again, as in viscosity mixing, the rate is not a linear function, mathematically speaking, but it is logarithmic.