Mixing 5w20 with 5w30 and 15w40

[peterr]

Inspired by the other experiences of mixologists, the features of the Canadian winter, my Auto-RXing of several cars, I am into some tame mixology. Looking for comments.

I just finished the 1st Auto-RX Rinse cycle of the >100K mile program on my recently acquired Winter car which has about 145K Miles. I was struck by how dirty the oil looked and a fair amopunt of grit and thicker sludgy stuff settled out.

Anyhow to run the second clean cycle i had two litres of Castrol GTX 5w30 (the recommended grade for this 1994 Mazda MX-3 with the 1.8L V6) and I mixed that with 2 litres of Castrol GTX 5w20 and the 9 ounces of ARX.

Here is the deal, I really love the 15w40 Esso Xd-3 HDEO dino and I saw the GTX 5w20 on sale for cheap, and I figured that a mix of the two would make a good mix for my second ARX rinse cycle (should start in April, when pure 15w40 may still be too thick for Canada weather).

Thoughts on these two 50/50 mixes in my engine and climate?
Castrol GTX 5w20 and Castrol GTX 5w30
Castrol GTX 5w20 and Esso XD-3 15w40

 

[LargeCarMan]

I personally would keep the same brand and lower numbers of the oil(5)the same with your blend.I understand the top numbers (20&30) will make a good top number blend. Viscosity improvers of different natures (5)vs(15)might not mix well.

Reading many posts here have convinced me that certain base stocks should not be mixed...stay with one brand when blending. Of course analysis of blends and/or proven blends do work.

With 145,000 on the engine, the Esso 15-40 straight with the ARX should be fine for your rinse cycle...even in the Spring in Canada.

I hope a person with knowledge gives us some words of wisdom on this. All of us have done this and the truth needs to get out.

 

[Ray H]

(You might wanna peruse my latest UOA...)

 

[peterr]

Yes, I was running 10w30 in November and early december. I think it likes 5w30 best, but no real issues with the 10w30 in moderately cold weather.

Right now I have the Castrol 5w20/5w30 mix in during colder weather and I expect that it just makes a thin 5w30 with no additive clash due to the common Castrol-ness.

My thinking was that the comnbined 5w20/15w40 would be a reasonably okay oil for april weather and that I might be getting better cleaning and a better quality oil with the mix vs a straight 5w30 or 10w30, particularly in Auto-RX applications

The total cost of these blends will work out to a little less than $1.70 US per quart. Up here in Canada we don't see the $0.49 chevron or $0.99 havoline. $1.70 is about what the cheapest oils commonly available like Wally world Tech2000 Dino or CDN Tire Autolab cost. While this is most definitley not about cost I do want to consider that the I might get something better for my application through the mix of two premium oils:

Castrol GTX 5w20 (my understanding is that all of the 5w20s are good oils just to meet the spec. Normally 5w20 costs more than 5w30 or 10w30 in my local market)

Esso XD-3 15w40 HDEO (an extremely well regarded oil with the cleaning abilities inherent in a quality HDEO)

 

[hominid7]

If it was my car, i'd stick with 5w30 or 10w30. I'm not a fan of mixing.

 

[LargeCarMan]

With 3,000 miles only and the viscosity starting to go low...could this be an indication that mixing different viscosity's harm the oils viscosity index?

From peterr:

(You might wanna peruse my latest UOA...)

From Blackstone labs:
The viscosity was mildly low, but since it's not being caused by a contaminant, it's okay.

 

[peterr]

RayH

This one?
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=003260

Interesting "swampwater" results. Makes me feel okay about my comparatively tightly scoped combos.

 

[m2200b]

The 15-40 mix is a thick 10-30. My similar age mazda prefers 5-30 for lifter noise but I assume you've run 10-30 and know whether your MX3 will tolerate thick 10-30.

 

[427Z06]

quote:

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Originally posted by Ray H:
(You might wanna peruse my latest UOA...)

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Well it could be noted that yours was a mundane mix of all 10w30 cheap dinos, used for only 3000 miles in a mundane engine, driven mundanely in a mundane climate.