Blending Advice Needed, please

[BTLew81]

I have a 2007 Mazda3, which specs 20wt. I usually use 30wt, as I can keep one oil in the garage. I have a chance to get some Rotella 15w40 CHEAP.

So, my question is, with a 5 quart capacity, how much 5w30 would I have to blend into the 15w40 to get near a 10w30 for summer running?

I like the HDEO, so if I can blend it down a bit and get it cheap, I'd like to do this.

Thanks.

 

[SuperDave456]

I think you are getting your numbers confused.

You would need to mix a Xw20 with a Xw40 to get somewhere around a Xw30 weight oil.
If you start mixing Xw30 weights and Xw40 weights you will only end up with a Xw35 or so.

The first number only relates to very cold temps, so it dosent matter for a summer oil.

If I were you I would pass on the 40 weight in this car. It being so new and spec'd for somethign much lighter.

 

[TallPaul]

A WAG would be that anything from no more than 2 qts of the 15w40 out of 5 to stay within the 30 weight 100cSt viscosity range. Not to worry about the front (w) number as it's summer. Get the actual 100C viscosities of both oils and calc for a 12 cSt brew.

Could also blend that Rotella with a straight 30 for a more robust base.

 

[addyguy]

It may be cheap, but on a new Mazda, that assume is still under warranty, you don't want to start blending 15w40 HDEO into the mix. As SuperDave said, it would still be a very thick mix.

Just stick with a PCMO 30-weight for the next couple of years, then do what you want!

 

[Billy_D]

I thought your Mazda is spec'd for 5w20

 

[bepperb]

I mean, how cheap are we talking here?

Formula shell can be had for ~1.25 a quart pretty regularly. I'd run that in a 5w-20/30 before any of this nonsense.

Rotella is a good oil, but you're so far off spec it doesn't make any sense. The money you save will be wasted on the extra gas you use running ~35 weight.