Mixing 5W30 and 10W30 oil

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

Reply to
Jungwoo Ha
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Jungwoo Ha wrote in news:ef1i7q$ai5$ snipped-for-privacy@news.cs.utexas.edu:

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.

Reply to
XS11E

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.

Reply to
Lanny Chambers
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.

Reply to
M. Cantera

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

Jungwoo

Reply to
Jungwoo Ha

the same thing happened to me... more tapping on start up with 5w30 than

10w30. nice to know i am not alone.
Reply to
Christopher Muto

"M. Cantera" wrote

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......

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Ken

Reply to
Ken Lyons

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

Reply to
Dana H. Myers

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

Reply to
M. Cantera

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