Mixing 10W40 and 0W20 to get 5W30?

[mrdctaylor]

So I picked up a bunch of 10W40 synthetic (both in the HM Castrol and HM M1 varieties) on clearance for cheap. I ended up selling one of the 2 cars I was planning to use it in so it will take me a bit longer to get through the stash now. I was toying with the idea of mixing it 50/50 with some 0W20 and using it in a different vehicle as well. That should give me (roughly) 5W30-ish oil, right? Are there any real downsides to doing this?

 

[FermeLaPorte]

There's a formula around that lets you calculate the resulting viscosity when you mix oils. Depending on the viscosity that you get, and in what xw-x that viscosity is on range, that is what you get. I'm not good with math so you'll have to calculate it.

 

[parshisa]

Check this one out

http://www.widman.biz/English/Calculators/Mixtures.html

 

[NGRhodes]

Edit, beaten. Doh.

 

[mrdctaylor]

Ok, so I used this calculator.

M1 HM 10W40 cSt @ 100 deg = 16
M1 AFE 0W20 cSt @ 100 deg = 8.7

Mixing 50/50, the calculator gives me a cSt of 11.69 (the average would've been 12.35).

M1 5W30 has a cSt of 11.0. So we are definitely a 30 weight. Looks good to me.

 

[69GTX]

The top grade is the easy part. And no problem mixing for that.

But when you mix 0w and 10w that's the tricky part. There have been examples of mixing different oils that gelled up right around the freezing point. If I dared to mix 0w and 10w, I'd probably only want to do that in summer where ambient temps are well above freezing.

 

[mrdctaylor]

A 10W40 is good below freezing by itself, isn't it? Why would adding a 0W20 to it cause issues? Is there something else at work here?

 

[weasley]

I'd be surprised if you would get the CCS and MRV needed for a 5W - you might luck in but in the end you might get something that doesn't meet any SAE J300 demands, or might stay at 10W - it's difficult to know how the various base oils, viscosity modifiers and pour point depressants will work together. You'll end up with an unholy formulation that would never be blended under normal circumstances (potentially 4 or more base oils, 2 VMs, 2 PPDs, 2 different DI packs along with whatever other boosters and supplements).

It might work, it probably won't be catastrophic, but it will be a compromise.

 

[ammolab]

I have mixed VR-1 10w30 and 20W-50 50/50 for years to get a ?W-40 for my BMW Bike. After 5000+ miles it has always tested a good 40 weight....works for me.

 

[JimPghPA]

The low number is all about at what temperature the oil turns into a wax.

The molecules of the 10W will still turn into wax at the same temperature they did before they were mixed with the 0W.

 

[demarpaint]

Use it up in the spring summer and don't bother mixing it. You live in Texas it should be fine, especially in the two older vehicles in your fleet. Or sell it, and make a possible profit.

 

[A_Harman]

The low temperature number is unpredictable, and the best you could hope for would be a 10w30, same as the higher W-number of the two oils you are blending. If you blend with a 0w20 from the same manufacturer, and the additive packages are compatible, maybe you would get a 5w30. For example, if you have M1 10w40 High Mileage, blend with M1 0w20 High Mileage. Since you are in Texas, the low temperature performance probably isn't critical.

 

[Triple_Se7en]

Originally Posted By: mrdctaylor
Ok, so I used this calculator.

M1 HM 10W40 cSt @ 100 deg = 16
M1 AFE 0W20 cSt @ 100 deg = 8.7

Mixing 50/50, the calculator gives me a cSt of 11.69 (the average would've been 12.35).

M1 5W30 has a cSt of 11.0. So we are definitely a 30 weight. Looks good to me.


Yep, close enough and blending oils is fine. But I generally don;t do it using HM oils with non-HM oils. But it won't hurt anything - or shorten your OCI, so carry-on.

 

[Crispysea]

I’ve been thinking about this also. I have lots of 0w-20 from AAP clearance, and lots of 10w-40 from AZ clearance. I even have a few 20w-50 quarts. I checked that calculator a few times. To get 5w30 viscosity (10 cSt@100C), it’s roughly a 2:1 ratio for 10w-40, and 3:1 for 20w-50.

 

[SubieRubyRoo]

You WILL NOT get a 5W by mixing a 10W and a 0W. Mixing will not change the behavior of the waxes in the 10WXX oil. At best, if you mix say a 10W40 and a 0W20, you will get a 10W30 at 50/50 ratio.

 

[mrdctaylor]

For my purposes, 10W30 is fine. As has been stated, I live in Texas and it doesn't get too cold. I've run 10W30 in my Tacoma in the winter with no issues.

 

[A_Harman]

Originally Posted By: SubieRubyRoo
You WILL NOT get a 5W by mixing a 10W and a 0W. Mixing will not change the behavior of the waxes in the 10WXX oil. At best, if you mix say a 10W40 and a 0W20, you will get a 10W30 at 50/50 ratio.


But since the concentration of whatever waxes in the 10W-XX is diluted, it would seem like the viscosity would be lower due to the 0W-XX component that hasn't yet formed waxy particles at a given temperature.

I would really love it if we could find a way on BITOG to test the low temperature properties of such mixes.

 

[Crispysea]

I’m not concerned with the winter grade, especially this time of year. If I can get 30W at operating temperature, that’s all I need. It rarely gets below freezing where I am.

 

[LckydevL]

I mix (2) 5W20, (2) 5W30 and (2) 10W30 just to cover all the basis in my 5.3 Vortec.

The first 4 quarts are plain Pennzoil and the 10W30 is Ultra from a long ago clearance buy.

 

[ammolab]

Originally Posted By: SubieRubyRoo
You WILL NOT get a 5W by mixing a 10W and a 0W. Mixing will not change the behavior of the waxes in the 10WXX oil. At best, if you mix say a 10W40 and a 0W20, you will get a 10W30 at 50/50 ratio.


Be careful Texans! Those waxes in your 10w30 oils or ?W-30 mixes can cause troubles at -33 degrees Fahrenheit....keep your eyes on the forcast!