motor oil mixing

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  #1  
Old 05-24-09, 10:15 AM
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motor oil mixing

Why is it not recommended to mix motor oil types/brands when changing the oil in your vehicle? The recommended viscosity for my vehicle, in my climate, is either 5-30W or 10-30W, and with an oil and filter change the refill amount is 4 1/2 quarts. So when I buy quarts of oil when it's time for an oil change, I usually buy it on sale at different places at different times when they happen to have one or the other of those viscosities of whatever brand on sale. So if I buy five quarts, then I end up with half a quart left over after the oil change. Then the next time I buy oil I might just get four quarts so I can use up what's left from previous. But what's left from previous often happens to be a different brand or maybe the other viscosity, so I could end up with putting half a quart of slightly different oil type in with the other four quarts of the same. Is this a big no-no and if so why is it so terrible?
 
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Old 05-24-09, 10:34 AM
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Mixing brands of oil is ok, diff visco is not recommended. In the real world I doubt 1/2 qt of one mixed with 4 of the other would make much difference.

Now you don't want to mix synth with real dino oil...at least all I've read says that.

You never need to add oil between changes? The 1/2 leftover would seem perfect for that.

As to the whys of it all...not a petro engineer..so can't tell ya.
 
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Old 05-24-09, 10:52 AM
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Originally Posted by Gunguy45 View Post
Mixing brands of oil is ok, diff visco is not recommended. In the real world I doubt 1/2 qt of one mixed with 4 of the other would make much difference.
Now you don't want to mix synth with real dino oil. You never need to add oil between changes?
In the real world I figured too that 1/2 qt of one visco mixed with the other (5-30W and 10-30W) couldn't really hurt. And I don't use synthetic, so that doesn't apply with my issue. No, I never really need to add oil between changes (every 3000 miles), so I often have half a qt left on hand to use up with this particular vehicle. Also, I was thinking since both vicsosities are ok to use, and I don't know which viscosity would necessarily be any any better than the other for my vehicle in my climate (says both are okay in the owners manual) maybe I could just compromise and put in half 5-30W and half 10-30W. What could it hurt, maybe that would even be be better?

Ditto issue with anti-freeze/coolant. Apparently it's so terribly bad to mix brands. If the anti-freeze coolant is the regular glycol green type, does it really matter? And again, I'm talking about the real world here.
 
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Old 05-24-09, 11:04 AM
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Same thing I would think with the antifreeze....but there are so many different types with different properties you'd have to be real careful. Color is no longer a good indicator of type.

On a similar vein...you'd think I could put summer blend windshield washer fluid right in with the winter blend (RainX bug remover summer, and RainX antifreeze type in winter). Butttt Nooooo...when I first did it it turned into this lumpy brown gook type stuff. So now when I do it, I have to drain the old out of the tank, add water, flush the pump and lines, then refill.
 
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Old 05-24-09, 11:37 AM
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Originally Posted by Gunguy45 View Post
you'd think I could put summer blend windshield washer fluid right in with the winter blend (RainX bug remover summer, and RainX antifreeze type in winter). Butttt Nooooo.
Maybe you should get a jug of the "2-in-one" RainX washer fluid stuff shown here in the gallon container. It removes bugs AND doesn't freeze. It's the best of both worlds, real world included. Rain-X: All Season Bug Remover with Rain-X Original Treatment
 
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Old 05-24-09, 12:07 PM
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Well I've never even seen that..maybe it wasn't carried last time I bought.
Have to check it out when I finish the jug and a 1/2 of the other two I have..

At 400 miles a month...that could be a while....lol
 
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Old 05-24-09, 05:46 PM
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I do the same as you do. I buy whats on sale and put it in as needed.
I think that being some oils have stronger detergent then others that it is possible that engine sludge could be loosened from and engine that was use to a mild detergent motor oil.
But if the engine is a clean engine I cant see it making much of a difference.
But as the person stated above, I also am not no oil engineer
 
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Old 05-24-09, 06:13 PM
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as far as brands, it doesnt matter. viscosities it does tho. using the two different types seperate is fine just dont alternate between oil changes. keep you vehicle on one or the other throuout the year. for u i would reccomend putting the 10w-30 in the summer and warmer months and using 5w30 for the colder months. 5w30 is a thinner oil compared to the 10w30 and mixing the two together would cause seperation between oils and would work properly and may give u problems down the line. you may not see it now but later on in your vehicles life problems might occur. basicly find which one your car runs better on and stick with it
 
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Old 05-26-09, 06:38 AM
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Horrible things will not happen if you mix oils.

Mixing different brands is okay.

Mixing different viscosities is okay. You'll end up with a viscosity somewhere in between the viscosities listed on the bottles.

Mixing synthetic with regular oil is okay. You'll end up with a semi-synthetic, same as what is popularly available on the shelves.

All API-rated motor oils should have detergents. There are some exceptions, but they are meant for your lawn mower.

So go ahead and do what ever suits the management of oil stock in your garage.

I agree with not mixing different types of antifreezes, unless you know what you're doing.
 
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Old 05-26-09, 08:56 AM
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Originally Posted by rednecksputter View Post
mixing the two together would cause seperation between oils and may give u problems down the line. find which one your car runs better on and stick with it
To me it seems the car runs no differently on either viscosity, 10-30 or 5-30. The recommended viscosity according the vehicle manual can be either, depending on the climate temperature range, both of which match the temperature range in my area and where I drive.

Is it a fact that if I mix the viscosities it would cause separation and problems down the line, as you state? Others in this thread, including me, tend to think it's probably okay to mix and won't hurt anything.
 
  #11  
Old 05-26-09, 01:02 PM
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Long ago I read a study from which I understood:
1... one should use say, 5-20 rather than 5-30 (narrower )
2... one should use this-that brand rather than ( 6 others) (minerals present)
3... one should use high-detergent (coincidentally most of the #1, #2 mentioned.
Later, a post from (here?) saying diesel oil is okay for cars, has high detergent
........
AFAIK if one finds that study online, follows those brands, and the same guidelines
above one would have one's engine last longer than the recommended
one-viscosity any-brand method
 
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