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ChevyMan
11-24-2007, 04:18 AM
What's wrong about mixing 30 wt oil with 10w30 oil?
I have 10w30 as the principal oil in my car but when
it shows "low" on the dipstick I top it off with straight
30 wt.

mrblanche
11-24-2007, 07:14 AM
Nothing wrong with it, as long as the oil types are compatible. But it's not accomplishing anything, either.

First, you have to understand what 10W30 means. That is, it's an oil that pours in low temperatures like a 30 wt would at high temperatures, but maintains its relative 30 wt viscosity up to high temperatures. The little trick that makes this possible "wears out," so eventually it tends to get thinner at the high temperatures. So adding 30 wt might even help it stay in viscosity longer.

Eric
11-24-2007, 07:36 AM
What's wrong about mixing 30 wt oil with 10w30 oil?
I have 10w30 as the principal oil in my car but when
it shows "low" on the dipstick I top it off with straight
30 wt.


As Mike said, no real harm from mixing viscosity. But I would be concerned about using ancient 30wt oil that maynot be even close to current API specs for use in a modern engine... it's very important to use an oil that has at least the minimum rating, as found in your owner's manual.

DonTom
11-24-2007, 09:29 AM
Here is some good info on motor oils which includes information on mixing:

http://www.citgo.com/ConsumerProducts/Oils/EngineOilMyths.jsp
(http://www.citgo.com/ConsumerProducts/Oils/EngineOilMyths.jsp)
-Don-

Dave Brand
11-24-2007, 10:12 AM
For a good, concise explanation of viscosity, see;

http://www.valvoline.com/carcare/articleviewer.asp?pg=ccr20040601ov

....and note that it's viscosity, not weight! ::)

ChevyMan
11-24-2007, 05:05 PM
What's wrong about mixing 30 wt oil with 10w30 oil?
I have 10w30 as the principal oil in my car but when
it shows "low" on the dipstick I top it off with straight
30 wt.


As Mike said, no real harm from mixing viscosity. But I would be concerned about using ancient 30wt oil that maynot be even close to current API specs for use in a modern engine... it's very important to use an oil that has at least the minimum rating, as found in your owner's manual.


The reason I asked the mixing question is due to the fact that I used to use straight 30 wt Pennzoil for many years and just recently switched to same brand 10W30 and I happened to have a qt of #30 left over and used it to bring the level up to "full". Sure I could use 10W30 but why discard the 30wt (same API as the 10W30)?

Larry

Eric
11-24-2007, 06:14 PM
What's wrong about mixing 30 wt oil with 10w30 oil?
I have 10w30 as the principal oil in my car but when
it shows "low" on the dipstick I top it off with straight
30 wt.


As Mike said, no real harm from mixing viscosity. But I would be concerned about using ancient 30wt oil that maynot be even close to current API specs for use in a modern engine... it's very important to use an oil that has at least the minimum rating, as found in your owner's manual.


The reason I asked the mixing question is due to the fact that I used to use straight 30 wt Pennzoil for many years and just recently switched to same brand 10W30 and I happened to have a qt of #30 left over and used it to bring the level up to "full". Sure I could use 10W30 but why discard the 30wt (same API as the 10W30)?

Larry




That should cause you no problems; your '70s-era Chevy doesn't require the highest grade stuff being recommended today. There is, however, one catch - and it is that for emissions reasons, oils are being formulated with less zinc these days and in older engines with flat tappet cams (like yours) this may cause excessive wear and even failure.

A lot of really solid people in this field recommend using either GM's additive or switching to Ames Oil, Rotella, or Red Line to avoid any problems...