Castrol's view on mixing oils

[buster]

Originally Posted By: aa1986
I sent an email to Castrol asking about mixing grades within the same brand and also mixing across their brands.

In short, the only thing they say is ok in terms of mixing, is topping off with the same grade of oil. If you do this a lot, make sure it's the same formulation. Anything else in terms of topping off and mixing is not recommended. Here are the key points of the reply I got:

- For topping off: You can use any of their products / formulations so long as it is the same grade. They do not recommend topping off with another grade.

- They do not recommend topping off with a different formulation on a continuing basis.

- Do not recommend mixing different grades even in the same formulation.

- Do not recommend mixing formulations due to changes in viscosity that can develop. (This is something Shannow pointed out).

- They said that Edge gold bottle with Titanium FST is not the same as the Edge gold bottle extended performance.



I've said this all along. It's common sense.

In fact, ask any formulator this and they will say it's OK to do for top off, but ideally you want to stick with the same chemistry.

Some on this site have been misleading folks to think otherwise all because of VI, which again is ridiculous.

 

[fdcg27]

I don't know about you, buster, but what I find most amusing in this thread is the way so many posters are eager to discount the advice of a major blender.
For some, it appears that hearing something from the horse's mouth only counts if the horse is telling them what they want to hear.
Many posters also appear to use lack of engine death as their standard of acceptable mixed oil performance although we should all know that any ill effects of indiscriminate mixing will be far more subtle.
Those desiring higher VI oils could also simply buy such oils to begin with rather than trying to blend their way to them.

 

[wemay]

I guess that term keeps coming up, "compatible does not mean ideal".

 

[buster]

Originally Posted By: fdcg27
I don't know about you, buster, but what I find most amusing in this thread is the way so many posters are eager to discount the advice of a major blender.
For some, it appears that hearing something from the horse's mouth only counts if the horse is telling them what they want to hear.
Many posters also appear to use lack of engine death as their standard of acceptable mixed oil performance although we should all know that any ill effects of indiscriminate mixing will be far more subtle.
Those desiring higher VI oils could also simply buy such oils to begin with rather than trying to blend their way to them.


Exactly. One member in particular was giving out very bad advice and was not a chemist or formulator. Gotta love internet experts.

This is so common sense it makes me wonder why it's even discussed.

 

[aa1986]

It makes sense not to mix oil, but there are going to be occasions where it is unavoidable or done unwittingly.

The average consumer, let alone the most anal BITOG types, won't know when a formulation has changed within the same product, within the same viscosity.

So the only sure way of not mixing is to buy your oil in exact quantities and check the production dates on the bottles.

 

[Shannow]

Originally Posted By: wemay
I'm not a chemist but my layman's common sense would 'suggest' that mixing two SN, 5w20 oils would yield the same. The additves of each being diluted if using different packages of course. As for mixing different viscosities, I wouldn't now, but I would assume a viscosity somewhere in the middle?


I used to think the same thing, in light of what was being promoted here...and if the lubricant's properties were purely basestock derived, I'd say it would be correct.

Problem is that for intuition to be correct, the different manufacturers must behave linearly, and collectively...in the basestock brew that you have as a result.

By linearly, I mean that half the treat rate of each player's PPD, VII, FM, whatever must do exactly half the job. By collectively, I mean that the two additives that are being expected to do exactly half a job, do that half job at the same time as the other's additives, so that the two half jobs add up to the original full package...in the new basestock blend.

All of those ducks having to line up to say for certainty that two oils, even of the same grades can't be guaranteed to make the same grade when mixed.

Having read a lot more on the subject, it's the cold end, the xW that typically suffers (and most people are never testing that part of their oil regularly with starting at pumpability limits), but as KCJeep found out, it can be any part of the equation that (sometimes) doesn't play right.

 

[wemay]

Keeping an open mind and accepting that long held beliefs may be incorrect or at least disputable is important when presented with multiple studies and enough reading. Thank you for sharing the info.

 

[Shannow]

wemay,
tried to kick off a discussion last month on a paper I found, which demonstrates that some of the additives are very non linear in behaviour, when alone, and mixed.

Discussion of a paper on behaviours of various additives

 

[KCJeep]

Originally Posted By: Shannow
KCJeep... This the one ?


Yes that's it. I meticulously calculated and measured i should have been about 10.5 or a bit more at cst100. Nope!

Good point on the second one posted though i had forgotten about that one. Better results with one quart 5w20 in a fill of 10w40.

I have not done any blending like that in a while now.

 

[camrydriver111]

Originally Posted By: aa1986
It makes sense not to mix oil, but there are going to be occasions where it is unavoidable or done unwittingly.

The average consumer, let alone the most anal BITOG types, won't know when a formulation has changed within the same product, within the same viscosity.

So the only sure way of not mixing is to buy your oil in exact quantities and check the production dates on the bottles.


Has anyone brought up this point to Castrol? We might be mixing oil without even knowing!

 

[fdcg27]

I saw that thread and found it interesting.
I've since decided that intentional mixes should probably be limited to warm weather use, where the loss of low temperature performance won't be as important.
I also now understand your advocacy of a 30 grade for top-ups, since such an oil would have no VIIs to interact with those of the oil already in the sump.
You've also helped to clarify the extent to which all API spec oils are actually compatible. Not necessarily so much, apparently.

 

[wemay]

http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3572108/2/2.4l_kia_optima_recommendation


The topic is at best a point of contention whether folks here agree or not. Many other respected entities like Blackstone Labs are keen on the idea that mixing has no ill effects as mentioned by them in the comments section of the UOA on page two of the thread included above. This will rage on like thin vs thick and CAFE vs protection. But as mentioned in those papers presented by Shannow, I'd be more reluctant if living in the great white north.

 

[HKPolice]

Hmm I guess the pro mixing crowd on BITOG has no opinions? I expected a lot of people to provide first hand experience on how their 300K mile car has seen nothing but mixed oil and still works like new?

 

[wemay]

Yeah, I wouldnt mix two brands anymore. At most, I'd mix conventional with synthetic of the same brand and viscosity to have a handle on the percentages.

 

[wemay]

Nah, I would still mix brands and viscosity etc. so long as the mix falls within range of the vicosity spread needed.

OCD......