mix 10w 30 with 5w 30 ?


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Old 09-01-18, 03:08 PM
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mix 10w 30 with 5w 30 ?

The owners manuals for a couple vehicles I own describes on the little chart the temperature ranges with which either 5w 30 motor oil or 10w 30 can/should be used. In my neck of the woods it's usually right in between both and I've used both, one or the other, for years when changing oil on these vehicles. Any big deal or big no-no about mixing the two if I wanted to? I have a couple quarts of the 5w 30 leftover and a couple-three quarts of the 10w 30 on hand leftover too so was just thinking of mixing them together to refill the crankcase after draining the old oil on my next oil change I'm getting ready to do.
 
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Old 09-01-18, 03:13 PM
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Unless they are performance vehicle, go ahead and mix the two. I've done that many times in the past with no adverse affects. All you're doing is changing the viscosity and blending the two. If you know for sure you're going operate in the extremes of either of the two ranges then stick with the one that fits the temperature.

However, never, NEVER do this on today's cars especially with synthetic oil.

I assumed these were yard type vehicles like lawnmower or tiller or maybe a snow thrower.
Just realized the forum section is cars. But my suggestion remains the same if the cars originally asked for just one of the two choices and are older than 8 to 10 years (when did cars totally switch from bio to syn oil?).
 
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Old 09-01-18, 03:21 PM
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I assumed these were yard type vehicles like lawnmower or tiller or maybe a snow thrower.
Well, no. These are not yard type vehicles. Regular car and regular pickup that use regular oil.

Edit: Oh okay saw your edit, where your suggestion remains the same. So sounds like I'm good to go. Thanks Norm201.
 
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Old 09-01-18, 03:22 PM
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Yea, I revised my reply with edits.
 
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Old 09-01-18, 03:32 PM
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How about mixing brands? probably fine too, even though they'll tell you not to?
 
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Old 09-01-18, 04:02 PM
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Different manufacturers use different additive packs to achieve certain parameters .
If you mix viscosities/manufacturers you may very well be diluting (watering down) the additive ingredients and compromise the ability of the oil to do it's intended job.

A few quarts of oil is cheap and well worth the small price to maintain the integrity of the same brand/viscosity additive pack to do it's intended job.
The wrong FrankenBrew may just cause issues and you'd kick yourself for trying to save $5.00 and costing $500.00

Most manuals say you can add a quart of off brand out on the road if you need it (the wrong oil IS BETTER than no oil) but change it at the earliest convenience.

In AK I would stick with 5W-30 ...in AL I would go 10W-30
 
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Old 09-01-18, 04:19 PM
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In AK I would stick with 5W-30 ...in AL I would go 10W-30
Well I'm actually in southeast AK (moderate temps) where the temperature extreme might be 10 degrees F at the lowest (rare) and 80 degrees F at the highest (also rare). 10W-30 okay, or what?

Probably will steer clear of mixing brands then I suppose, even though I can't really understand how it would "water down" the additive packs to any considerable harmful effect. Maybe it does, if you say so, so like I said will avoid doing that I guess.
 
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Old 09-01-18, 04:52 PM
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You need to know (see) how different oils are blended to achieve certain values.
The Petroleum Quality Institute of America is a great place to see virgin oil analyses of different brands
http://www.pqiamerica.com/
Pick "passenger car oils" and look at all the different brands - check the ingredients in each to see how they achieved their API rating ... they are all different BUT THEY ARE A SPECIFIC RECIPE OF INGREDIENTS TO DO THE JOB.
When you mix oils you get a hodge-podge of additives that are either too much or too little for the rating and the job.
Get the picture ??
Lots of reading and homework to do to answer your initial question
 
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Old 09-01-18, 05:11 PM
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Got the picture, on mixing brands. On my initial question (whether it'd be okay to mix 5w-30 with 10w-30), that's where you'd recommend me doing a lot of reading and homework? Or the question whether 10w -30 is gonna be okay here as opposed to 5w-30?
 
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Old 09-01-18, 05:48 PM
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Oil is a very interesting product, and certainly there is alot of engineering that goes into determining what is fit for purpose.

But, on a practical basis, when you drain oil, you don't get it all out. Most engines retain at least .5 quarts, some as much as 2 quarts, especially deisel engines. You can see this difference in the "dry" engine fill verses the oil change fill, both specifications which are often in the owners manual, certainly in the workshop manual.

Since all oils are at the least nominally compatible with all oils available on the market, synthetic or otherwise, using different grades or brands is allowed, as long as the oil meets the overall specifications for the engine (the SL, or SM or other car specific rating as per your owners manual, it is getting more complicated with dexos and Euro car specific ratings all of which deal mostly with emissions not oil perfomance per se). So mix away. Off the shelf synthetics all use very similar additives, not a surprise when they all have to meet the same specifications set out by the OEM car companies. Mixing synthetic with conventional probably improves on the conventional, but you do end up with "frankenoil" which properties under extreme conditions may not be as predictable. The main problem with such home brews might be leaking gaskets or seals, more than damage to the engine.

As to which oil viscosity to use, it should be ok to use either as both work at your temperature range. The only difference in the oils is their pourability at low temperatures, the 10 "w" (winter) means the oil is tested at 0 degrees, the higher 30 means it is tested at 212 degrees. When cold, takes 10 seconds to flow through a specific sized tube, or 30 seconds when hot. That's how the oil is graded by the SAE. Takes additives to get oil to behave like this, quite amazing chemistry really.

The 10W30 is kind of an old fashioned grade, and can be met with non synthetic base stock with viscosity improvers. Often the cheapest oil out there. 5W30 probably has some synthetic in the blend, and less of the viscosity improvers. Given the VI's wear oil with use/milage, I suppose the 5W30 might be the "better" oil with a more molecularly stable overall base stock. So for the same price, I suppose I would go with the 5W30. If you are chosing between full synthetics than this would be moot. Not sure if you are using synthetics? Also, most off the shelf "synthetics" are actually refined from conventional oil, so even that reference is becoming less relevant. eg. Castrol's products, even named synthetic, are refined from good old dino oil. This was not without controversy in the oil industry, but I suppose much like determining what food can be certified organic - lots of room for marketing.

But I think mixing grades/brands of the same key specification is what happens in the real world all the time.
 

Last edited by flatcrank; 09-01-18 at 06:07 PM.
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Old 09-01-18, 06:27 PM
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Update on my previous post about mixing brands -
I emailed a trusted friend who is a tribologist about this issue and he assured me that no ill effects would occur mixing the different brands ... so I stand corrected.

Mix On !!
 
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Old 09-01-18, 06:42 PM
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Flatcrank thanks for the very helpful lowdown there. My older "normal vehicles" don't require synthetics and I'm old-school anyway so I don't bother with them. They typically sell/stock both 5w-30 and 10w-30 here in the stores in my area (always have), and usually one or the other will go "on sale" from time to time. I suppose generally I should tend toward the 5w-30, although if no difference in price the old-school in me tends toward grabbing the 10w-30. I pay attention of course to the key specs in regard to what I buy, to make sure I don't get anything way off base. I decided now I probably won't worry about if I mix the 5w-30 with the 10w-30 or mix different brands very often.

And thanks 2granddaughters. I shall mix, MIX-ON!
 
 

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