Mixing multi weight and straight weight

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farrarfan1

farrarfan1

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After reading a lot of threads adressing the shearing of 5W30 and others on various home brew combinations I began to think about replacing a given percentage of 5W30 with straight 30W oil. For example, in a 5 quart system maybe running 2quarts 5W30 and 3 quarts straight 30W in the summer and reversing that in the winter. My thought is removing some of the 5W from the equation and replacing it with a straight 30W would result is less shearing. The actual percentage of each oil could be tailored to a particular climate or driving conditon. Is there any merit to this or am I way off base?
 
Oil shearing while it occorrs occasionally really has not been shown to cause higher wear numbers. Most times viscosity decrease is a result of fuel dilution.

Also in a vehicle with no other problems shearing is not that common especially in shorter drain intervals.

If you have a vehicle that is known to shear oil and drive long oil change intervals with conventional oil it might be a problem. But again-whether it will cause wear on the engine is speculative at best.

Going to straight viscosity to deal with an unfounded fear is not wise in my opinion.

What is your preferance for oil, distance, and driving habbits??
 
Al, the car is a 2004 Concorde, primarily driven by my wife to and from the school she works at(3 miles each way) and soccer pracrise, cheerleading practise,etc.. Once or twice a month it gets a 25 mile trip up I-65 to her Mother's house. Typical family car. I can use my work car off duty so there are some days the car gets 6 miles on the clock and that's all. Still under warranty so I am going with the 3month/ 3k oil changes. Up until I discovered this site I was a lifelong Valvoline (I hear the cringing) and Fram ( I hear the groaning) user.It has Super Tech full synthetic now but I've decided to just go with Havoline dino from now on. I guess I was looking at a way to "fortify" 5W30 and still keep the cold starting ability of 5W and strengthening the 30 end of it. This site has the uncanny ability to make a person think too much I guess.
 
F-fan - As far as home brews go, 5W-30 with SAE 30HD should be a very practical mix.

Take a close look at the viscosity numbers on the product data sheets.

You'll find most SAE 30's run 11 to 12 cSt @ 100C. The 5W-30's are in the 10's. So whatever percentage of SAE 30 added is going to jack up the average above even what the 10W-30's normally run.

But Chevron/Havoline SAE 30 is an excellent choice since it runs to the lower end of the SAE 30 viscosity scale.

Look at the viscosity spec's on the data sheet:
Havoline Product Data Sheet

On paper, a Havoline 5W-30 & SAE 30 home brew will generate a higher viscosity at startup, but still be a normal 5W-30 viscosity at full operating temperature. And due to the lack of VI's in the mono-grade 30 wt, it will be more shear resistant.

Have fun, mix away, & gain some practical viscosity knowledge in the process!
 
Well-I'll have to respectively disagree with the last poster, even though I am a fan of mixing. Fortifying with a 30 weight will cause harder starts (and read less pumping oil 'getting to where it need to get') The old adage about thicker is better has been shown not to be universally true.

I think you are right farrarfan1 to the concept of outthinking ourselves. Under the conditions you describe you could probably run all day long with a 20 wt. oil. Although I wouldn't recommend it due to not specified for your car and with shorter trips you will probably experience some dilution.

With your driving conditions and in your location (with fall and winter coming on)..Unless your car has some leaking injectors you are garanteed to do fine with a 5W-30 wt oil. I would consider though doing an oil analysis before warranty is up. You can go here.

Oil Analysis
 
quote:
Well-I'll have to respectively disagree with the last poster...
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LOL, thanks, Al. I actually take it as a compliment to have someone disagree with even the slightest hint of respect!

The reason Chevron/Havoline SAE 30 is a good mixing choice is due to the lower viscosity numbers compared to a traditional 30 weight.

Havoline SAE 30 is only 82 cSt @ 40C to begin with, not in the 95-105 cSt class of the "traditionals".

Here are the viscosity numbers, from a weighted average calculation, for the Havoline 5W-30, SAE 30 home brew:

2 qts 5W-30, 3 qts SAE 30 - 75.1 cSt @ 40C
3 qts 5W-30, 2 qts SAE 30 - 71.7 cSt @ 40c

So, in the mid-temp viscosity range, this mix is very similar to a 10W-30.

The cold start numbers are difficuly to approximate, as CCV data isn't listed for the SAE 30 grades.

From a coldstart viewpoint, I would think somewere from 30-40 degrees F, any mix ratio with over a quart of SAE 30 is no longer providing a practical benefit.
 
Great idea farrarfan1. If you want to thicken 5w30 that already is in the crankcase, the straight 30 would help, but for fresh fill I would go with a good 10w30 that has decent cold properties. Havoline might be it. (I am a Valvoline nut though, but not for AllClimate).

I mixed straight 40 into 10w40 to make a 15w40 (presumed) and am running it right now. I probably would not do it for winter though as am not sure of the cold properties. Could crudely freezer test compare though, I guess.
 
quote:
Originally posted by Blue99:

quote:
Well-I'll have to respectively disagree with the last poster...
Click to expand...
LOL, thanks, Al. I actually take it as a compliment to have someone disagree with even the slightest hint of respect!
Click to expand...
Hahahaha..unless either one of us can show the other a PhD in Tribology here..we are equal.
grin.gif
:

I guess my main point though is that if an engine can safely run hard at even 7 or 8 (and really lower) cSt. and since straight 30 weights are about 10 and will get thinner quicker past 100C what the necessity for using them. Do you really need a thicker oil at less than 100C?? I don't think so.

The other issue is that a straight 30 wt will be close to 2000cSt around 32F wher the 10W-30 will be around 500. Granted your mixture mixture will be a little thinner-maybe between 1000 and 1500 cSt. but again where would the benefit come in other than resistance to shearing.

But anyway just some discussion here.

Later
 
What we have to remember is that the straight weight oil is not going to directly interact with the hot temp weight of the multigrade. The straight weight oil will mix with the base oil of the multigrade (who knows it's viscosity?), thickening it and then the viscosity index improvers (VIIs) will spread more thinly over the whole mix. Increase in base oil viscosity, less VIIs per quart, final viscosity at operating temperature is probably similar to that of the multigrade to begin with, but you will have made the oil more robust by thickening the base oil.

For example: Take a small engine with a 4 quart capacity. Lets say you had a 5w30 with a base oil 100C viscosity (average) of 4 cSt and a finished (after VIIs added) 100C viscosity of 10. Now you add a straight 30 that has a 100C viscosity of 12. So three qts 5w30 and one straight 30. The base oil 100C viscosity will change: [(3 * 4) + (1 * 12)] / 4 = 6. So the 6 may be a good 100C viscosity of a 10wXX oil's base oil.

Now what do the VIIs do. Who knows? I don't, but for the sake of the example lets say we can use the ratio of the multigrade 100C viscosity to its base oil 100C viscosity, then: 10 / 4 = 2.5. But we are now spreading that over more quarts of the thicker base oil. Since the VII fortified oil is 3/4 the total mix, lets reduce the 2.5 by 0.75 to get 1.88 (way more precise of a number than what I am doing here, but...). Now the new base oil is 6 cSt, so 6 * 1.88 = 11.3. Well, if it were that simple, I would say the straight 30 not only thickened the base oil, but also gave the modified multigrade a higher viscosity. But the margin of error of what I just did is incalculable because I don't know how the VIIs act off the base oil, but you can see that it is rather complex however it works.

Am I freaking thinking about oil too much?
freak2.gif
 
Jeffersonville is almost KY - you seldom see a 0 degree F day. My guess is that your manual would indicate a 10w30 is fine for your driving conditions. A 5w30 for the Dec - Feb period may provide some slight benefit.
 
quote:
Originally posted by TallPaul:
What we have to remember is that the straight weight oil is not going to directly interact with the hot temp weight of the multigrade. The straight weight oil will mix with the base oil of the multigrade (who knows it's viscosity?), thickening it and then the viscosity index improvers (VIIs) will spread more thinly over the whole mix. Increase in base oil viscosity, less VIIs per quart, final viscosity at operating temperature is probably similar to that of the multigrade to begin with, but you will have made the oil more robust by thickening the base oil.

For example: Take a small engine with a 4 quart capacity. Lets say you had a 5w30 with a base oil 100C viscosity (average) of 4 cSt and a finished (after VIIs added) 100C viscosity of 10. Now you add a straight 30 that has a 100C viscosity of 12. So three qts 5w30 and one straight 30. The base oil 100C viscosity will change: [(3 * 4) + (1 * 12)] / 4 = 6. So the 6 may be a good 100C viscosity of a 10wXX oil's base oil.

Now what do the VIIs do. Who knows? I don't, but for the sake of the example lets say we can use the ratio of the multigrade 100C viscosity to its base oil 100C viscosity, then: 10 / 4 = 2.5. But we are now spreading that over more quarts of the thicker base oil. Since the VII fortified oil is 3/4 the total mix, lets reduce the 2.5 by 0.75 to get 1.88 (way more precise of a number than what I am doing here, but...). Now the new base oil is 6 cSt, so 6 * 1.88 = 11.3. Well, if it were that simple, I would say the straight 30 not only thickened the base oil, but also gave the modified multigrade a higher viscosity. But the margin of error of what I just did is incalculable because I don't know how the VIIs act off the base oil, but you can see that it is rather complex however it works.

Am I freaking thinking about oil too much?
freak2.gif

Click to expand...
Hey,

TallPaul, I see your posts and I really admire your knowledge of oil, yea it's scary but in a good way, lol Just thought I would chime in,,,AR
 
Well now that I explained how it works (or so I think), let me just add that Blue99 has the practicable method because we actually can get the 100C viscosity numbers for all the oils and we are only going to be ballpark (at best) anyway.
 
T-Paul, I've been slow getting back to this post due to reviewing the points made by yourself & Al.

5W-30 is probably not a good mixing choice due to the VI improvers & the difficulty in calculating the affect on viscosity numbers.

Also, as Al pointed out, SAE 30 has a rather flat viscosity curve when compared to temperature.

I now think that a 10W-30 is a better choice, rather than mixing, if any problems exist with 5W-30 shear.

But, for those of us who are "mixers", I'm always willing to "crunch the numbers" on these home brews.
cheers.gif
 
TallPaul,
Not trying to step on any fingers or toes but to me much of what you said is wrong.

quote:
What we have to remember is that the straight weight oil is not going to directly interact with the hot temp weight of the multigrade. The straight weight oil will mix with the base oil of the multigrade (who knows it's viscosity?), thickening it and then the viscosity index improvers (VIIs) will spread more thinly over the whole mix. Increase in base oil viscosity, less VIIs per quart, final viscosity at operating temperature is probably similar to that of the multigrade to begin with, but you will have made the oil more robust by thickening the base oil.
Click to expand...
The straight weight oil IS going to directly interact with the weight of the multigrade. How could it not they are mixed with each other? As we are all purchasing finished oil products there is no way to separate base oil from VII(viscosity index improvers) unless the finished oil has none added(single grade oil). You are correct that adding 1qt SAE 30 to 3qt SAE 5w-30 will increase viscosity of the 5w-30 at ALL temps. In fact it will probably be closer to 10w-30? Not sure on the 10w, maybe someone would chime in and give some guidance on this.

quote:
For example: Take a small engine with a 4 quart capacity. Lets say you had a 5w30 with a base oil 100C viscosity (average) of 4 cSt and a finished (after VIIs added) 100C viscosity of 10. Now you add a straight 30 that has a 100C viscosity of 12. So three qts 5w30 and one straight 30. The base oil 100C viscosity will change: [(3 * 4) + (1 * 12)] / 4 = 6. So the 6 may be a good 100C viscosity of a 10wXX oil's base oil.
Click to expand...
We have no way to figure or find what the base oil cSt of a multi grade oil is. Why? Because all we get is finished oil with VII already added to the base oil(s) and no way to separate them. So anything you could come up with would be a guess.

quote:
Now what do the VIIs do. Who knows? I don't, but for the sake of the example lets say we can use the ratio of the multigrade 100C viscosity to its base oil 100C viscosity, then: 10 / 4 = 2.5. But we are now spreading that over more quarts of the thicker base oil. Since the VII fortified oil is 3/4 the total mix, lets reduce the 2.5 by 0.75 to get 1.88 (way more precise of a number than what I am doing here, but...). Now the new base oil is 6 cSt, so 6 * 1.88 = 11.3. Well, if it were that simple, I would say the straight 30 not only thickened the base oil, but also gave the modified multigrade a higher viscosity. But the margin of error of what I just did is incalculable because I don't know how the VIIs act off the base oil, but you can see that it is rather complex however it works.
Click to expand...
The VII is what makes a multi grade oil multi grade. Using your example you could figure the viscosity at 40C and 100C cSt as these are given by the manufacturer. Add the four together and then divide by four. (3 * 10) + (1 * 12) / 4 = 10.5 cSt at 100C.

As Al and Blue99 pointed out the single grade has a flatter viscosity curve. If you wanted to bump the viscosity in a more linear way do it with another multi grade oil. Such as 5w-20 to lower or 10w-40 to raise the viscosity.

Personally I would just run one of the new Conoco/Phillips synthetic blend 5w-30's and forget about it.
 
Leanintoit: I think we both are right. Just we are looking at it from two different angles. Maybe I can clarify:

quote:
The straight weight oil IS going to directly interact with the weight of the multigrade. How could it not they are mixed with each other? As we are all purchasing finished oil products there is no way to separate base oil from VII(viscosity index improvers) unless the finished oil has none added(single grade oil). You are correct that adding 1qt SAE 30 to 3qt SAE 5w-30 will increase viscosity of the 5w-30 at ALL temps. In fact it will probably be closer to 10w-30? Not sure on the 10w, maybe someone would chime in and give some guidance on this.
Click to expand...
I believe the interaction of the straight weight with the multi-grade will be through the base oil thickening and then the VIIs will play off of that. I believe that is how it must be evaluated for purposes of accurately calculating the final 100C viscosity (or send a sample to Blackstone). It’s academic though, because we don’t have the base oil viscosity, nor do we know the formula for how the VIIs increase the viscosity at higher temperatures. Is the VII action linear, logarithmic, or what? I don’t know. No need to separate the VIIs from the base oil as the straight weight oil will naturally mix with the multi-grade’s base oil and the VIIs will collectively act off the thickened base oil.

quote:
We have no way to figure or find what the base oil cSt of a multi grade oil is. Why? Because all we get is finished oil with VII already added to the base oil(s) and no way to separate them. So anything you could come up with would be a guess.
Click to expand...
Right. My example is very hypothetical and for clarification only of what really happens (so I still believe). But we are limited to averaging the two oil’s 100C viscosities (as Blue99 has done).

quote:
As Al and Blue99 pointed out the single grade has a flatter viscosity curve. If you wanted to bump the viscosity in a more linear way do it with another multi grade oil. Such as 5w-20 to lower or 10w-40 to raise the viscosity.
Click to expand...
A straight weight or single grade oil has a flatter viscosity curve and lower viscosity index, and so does the base oil of a multigrade before the VIIs are added. In general(very general that is):

Adding a 5w20 to a 5w30 will reduce the 100C viscosity.

Adding a 5w20 to a 10w30 will reduce the base oil thickness and the 100C viscosity

Adding a 10w40 to a 5w30 will increase the base oil thickness and the 100C viscosity.

Adding a 10w40 to a 10w30 will increase the 100C viscosity.

Adding a straight 30 to a 5w30 or 10w30 will primarily increase the base oil thickness. So if one only wants to thicken the base oil that would be the way to go.

Of course, why mix when we have all these well formulated oils ready to pour? Well, I have only mixed (so far) to get rid of odds and ends or to thicken something already in the crankcase, instead of running with it or dumping the whole load. Once I had a crankcase full of fresh 5w30 and wanted to see what 10w40 would do for the oil pressure. I drained two qts off and added two qts 20w50 to approximate a 10w40. Worked pretty good, but I would never do it from the get go as there are good 10w40s available off the shelf.

[ September 21, 2004, 08:20 AM: Message edited by: TallPaul ]
 
Thanks to Al,TallPaul et al for your responses.
bowdown.gif
This idea came after going thru the UOA section. Shearing seemed to come up almost every time when 5W30 was analyzed. I took a simplistic approach and thought if you removed some of the 5W(less material to shear?) and replaced it with a straight 30W that wouldn't shear it might work. I was under the impression that the 5W part of the mixture would not be affected. In other words if the volume still contained a given percentage of the 5W component it would still function as a 5W. If that makes sense. I didn't take into account that it would change the composition of the 5W element in the mix. I was looking at it as simply making the 30 part of it a little purer with less material to shear, but still having some 5W to flow when the engine first starts.Oh well, guess I just proved you can't out engineer an engineer if you ain't an engineer.
 
If you mixed together equal parts Pennzoil SAE-30 and 5w-30 in a five quart system (2.5qts. each), you'd end up with:

viscosity at 40°C 78.7
viscosity at 100°C 11.0
viscosity index 128
 
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