Mixing 5W30 and 10W30 oil

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Jungwoo Ha - 22 Sep 2006 21:49 GMT

Hi,

I think it is safe, but since it doesn't hurt to ask,
is it okay to mix Mobil 1 10W30 with 5W30 on oil change?
I have one quart 10W30 leftover, and I want to put 5W30 for winter purpose.

Thanks,

Jungwoo

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XS11E - 22 Sep 2006 22:31 GMT

> I think it is safe, but since it doesn't hurt to ask,
> is it okay to mix Mobil 1 10W30 with 5W30 on oil change?
> I have one quart 10W30 leftover, and I want to put 5W30 for winter
> purpose.

That's a very interesting question, I read a bit of an essay on that
some time back so let me just rephrase a lot of technical stuff I can't
spell.....

Let me simplify by using straight weight oil, the viscosity is
determined by (here I'm going WAY of a correct technical explanation)
heavier oil having bigger molecules so if you mix one quart of 5 weight
and one quart of 10 weight together you do NOT get 2 quarts of 7.5
weight oil, what you get is one quart of 5 weight and one quart of 10
weight.

I probably won't hurt anything but I wouldn't do it. As a matter of
fact, unless you live in a very cold climate, I'd use 10W30 all year
around.

Here's what Miata.net says: "The manual also recommends a good quality
10W30 motor oil. Since then Mazda has recommended that Miata owners who
notice a tapping noise when starting a cold engine switch to 5W30 motor
oil. Synthetics are just fine, but engine treatments and other oil
additives are NOT recommended. If you live in an area with extreme
temperatures, consult your owners manual for oil and other fluid
recommendations."

I had the tapping mentioned and went the other way, from 5W30 to 10W30
and the tapping stopped in my engine. It also got quieter overall.

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Christopher Muto - 24 Sep 2006 13:39 GMT

<snip>

> I had the tapping mentioned and went the other way, from 5W30 to 10W30
> and the tapping stopped in my engine. It also got quieter overall.

the same thing happened to me... more tapping on start up with 5w30 than
10w30. nice to know i am not alone.

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Lanny Chambers - 23 Sep 2006 03:57 GMT

> is it okay to mix Mobil 1 10W30 with 5W30 on oil change?
> I have one quart 10W30 leftover, and I want to put 5W30 for winter purpose.

You don't need 5W-30 in Texas. Stick with the recommended 10W-30
year-round. It works fine for me here in Missouri, down to -10F. My
Miata is approaching 140k miles, runs like new, and uses no oil between
changes.

Signature

Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html

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Jungwoo Ha - 23 Sep 2006 16:15 GMT

>> is it okay to mix Mobil 1 10W30 with 5W30 on oil change?
>> I have one quart 10W30 leftover, and I want to put 5W30 for winter purpose.
[quoted text clipped - 3 lines]
> Miata is approaching 140k miles, runs like new, and uses no oil between
> changes.

Thanks Lanny.
Your word is like a bible to me :)

Jungwoo

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M. Cantera - 23 Sep 2006 05:35 GMT

5W30 and 10W30 use the same single grade 30 weight oil base. The
manufacturer adds friction modifiers (polymers) to make the oil flow
either like an SAE 5 or SAE 10 single weight at winter temperatures,
hence the 5W or 10W designation.

One can argue that it is better to use the 10w30 as is containg less
polymer and more oil, but I have no seen any literature that says
otherwise.

>Hi,
>
[quoted text clipped - 5 lines]
>
>Jungwoo

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Ken Lyons - 26 Sep 2006 03:10 GMT

> 5W30 and 10W30 use the same single grade 30 weight oil base. The
> manufacturer adds friction modifiers (polymers) to make the oil flow
> either like an SAE 5 or SAE 10 single weight at winter temperatures,
> hence the 5W or 10W designation.

I am not a expert on this, but I thought it was the other way around. The
base oil is SAE 5 or SAE 10 and the polymers puff up when heated, resulting
in a 30 weight when warm. Actually, the polymers uncoil......
http://flathead.rosenet.net/oil4sbc.htm

Ken

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Dana H. Myers - 26 Sep 2006 03:38 GMT

>> 5W30 and 10W30 use the same single grade 30 weight oil base. The
>> manufacturer adds friction modifiers (polymers) to make the oil flow
[quoted text clipped - 5 lines]
> in a 30 weight when warm. Actually, the polymers uncoil......
> http://flathead.rosenet.net/oil4sbc.htm

The above article matches the explanation I was once given by a
lubrication engineer, I believe it's correct. Basically, 5W30 is
an SAE 5 base-oil with an additive package to maintain viscosity
at higher temperatures (thus behaving like an SAE 30 oil when hot).

Way back when, in the mid-1980s I was road-racing motorcycles, and
one of the tuning tricks we used for dialing-in the damping of the
forks was to change the fork oil. We commonly mixed 5W and 10W
fork oil in varying degrees to get intermediate grades and the
effect was empirically pretty linear. I dunno how much engine
oil and fork oil differ, though I'd expect fork oil to have less
of a polymer package since it doesn't operate across the same
range of temperature as engine oil.

Dana

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M. Cantera - 27 Sep 2006 04:35 GMT

>>> 5W30 and 10W30 use the same single grade 30 weight oil base. The
>>> manufacturer adds friction modifiers (polymers) to make the oil flow
[quoted text clipped - 5 lines]
>> in a 30 weight when warm. Actually, the polymers uncoil......
>> http://flathead.rosenet.net/oil4sbc.htm

That is correct. I always remember the polymer in motor oil thing
backwards.

>The above article matches the explanation I was once given by a
>lubrication engineer, I believe it's correct. Basically, 5W30 is
[quoted text clipped - 11 lines]
>
>Dana

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