Originally Posted By: tr4petty
If I use 3 quarts of 5w30 Mopar oil and 3 quarts of 10w30 Mopar motor oil in my Grand Cherokee 4.0L, (it takes 6 quarts) will I get a 7.5w30 oil? Are there any problems with doing this?
The correct answer too the first question is maybe. Your math is wrong. You cant just avg 5 5 5 10 10 and 10 and assume your gonna get a 7.5w. The reason is to be called a 5w is simply must have a max viscosity of 3500cP at-25C. My point is it would depend on what you mixed. If you mixed a light 5w30 like PP and 10w30 like pp, half and half, you would simply end up with a 5w30. If your point is, will mixing a 5w30 with a 10w30 increase the cold weather flow of the 10w30, then again it is maybe. If they use the same basestocks then it would be yes the 10w30 should get less viscous at lower temps. But if you take a synthetic like Mobil 1 10w30 and mix it with a lower quality 5w30 conventional, there is a chance that you could make the 10w30 worse at very cold temps. If you really want to find what viscosity you have after mixing, you need to get the 40C and 100C viscosities off the manufacture data sheet and use this equation Vblend=EXP(((P1*LN(V1)+(P2*LN(V2)))/(P1+P2))) Where V1 and V2 are the viscosities of each oil at a temp. You will need too do it twice, one for 100C and once for 40C. P1 and P2 are parts of each. So if 3 qts of the fist then V1 is 3 and so on. This will get you very close to the blended viscosity. Sorry this got very long. Ill try to post a spreadsheet that does this for you in a new thread. To be the most accurate in blending, try to stick to similar oils. When mixing HQ synthetics with lower ones or dino, all bets are off and it is way to difficult to actually calculate it correctly. Hope this helped.