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#2379145 - 09/16/11 04:10 PM Mixing brands - same weight
gvken Offline


Registered: 08/24/11
Posts: 2
Loc: CA
I have 4 qts of Castrol Syntec 5w40, by car takes 8 qts. Is it safe to mix brands of the same weight? Say 4 qts of Syntec and 4 qts of Penzoil Ultra of the same weight?

Can't find Syntec anymore since they switched to Castrol Edge....

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#2379153 - 09/16/11 04:23 PM Re: Mixing brands - same weight [Re: gvken]
dparm Offline


Registered: 04/19/10
Posts: 12957
Loc: Chicago, IL
Old Syntec is now "Edge with Syntec". Old Edge is now "Edge with SPT" or "Edge with Titanium".

You can safely mix. It's not optimal but those two oils are not radically different enough to cause an issue. The theory is that their additive packages may clash but I've yet to see anyone prove that will cause problems.
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#2379230 - 09/16/11 05:31 PM Re: Mixing brands - same weight [Re: gvken]
edhackett Offline


Registered: 06/09/03
Posts: 1748
Loc: Sequim, WA
Here's your proof of at least one possible problem. It appears to be especially critical when using group III oils, as both of these are.

Mix of oils destroying cold flow properties:

http://www.infineum.com/Documents/Crankc...icants-2010.pdf

Ed
_________________________
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#2379249 - 09/16/11 05:46 PM Re: Mixing brands - same weight [Re: edhackett]
cmf Offline


Registered: 05/07/11
Posts: 415
Loc: Florida
Originally Posted By: edhackett
Here's your proof of at least one possible problem. It appears to be especially critical when using group III oils, as both of these are.

Mix of oils destroying cold flow properties:

http://www.infineum.com/Documents/Crankc...icants-2010.pdf

Ed


I wanted to read that article and it's a bad link!

Also from Valvoline's website:

» Can we mix two different brands of engine oils?
Technically it is possible to do so provided the new oil has the same performance level as the old oil. However, mixing oil brands (read topping-up) on a continuous basis is not a good idea. You should also be aware that engines typically go through a period of adjustment when making the transition from one oil to another. Because brands could be formulated with different additive chemistries, a new brand may act differently than the old one at first. Increased oil consumption and leaking seals are common adjustment problems.

Companies get their additive packages from a small amount of places and the possibility of issues isn't large, but it is there. I would not mix something like Red Line or Amsoil with off the shelf synthetics, but I would mix off the shelf synthetics with each other without worrying. My car very rarely encounters two oil changes in a row of the same brand of oil and I have no leaks or oil consumption FWIW.

In short, I agree with dparm that you wont have any issues mixing those oils.

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#2379256 - 09/16/11 05:51 PM Re: Mixing brands - same weight [Re: gvken]
edhackett Offline


Registered: 06/09/03
Posts: 1748
Loc: Sequim, WA
_________________________
Never attribute to engineers that into which politicians, lawyers, accountants, and marketeers have poked their fingers.

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#2379262 - 09/16/11 06:03 PM Re: Mixing brands - same weight [Re: edhackett]
cmf Offline


Registered: 05/07/11
Posts: 415
Loc: Florida
Originally Posted By: edhackett


Thanks, it was a great read and brought up a very important point that is overlooked: how well the oil performs after it's been aged in the engine for a few thousand miles.

Some important parts for lazy people:

"Ageing of the oil in service can have a profound effect on low temperature pumpability."

"R. Rhodes showed that mixing two well performing oils, commonly known as top-up, can result in a lubricant mixture failing low temperature pumpability."

The last part cites this: Rhodes, R.B., “Low-Temperature Compatibility of Engine Lubricants and the Risk of Engine Pumpability Failure,” SAE Technical Paper 932831, 1993, doi:10.4271/932831.

It's always great to read scientific papers on topics that are often hearsay.

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#2379614 - 09/17/11 06:15 AM Re: Mixing brands - same weight [Re: gvken]
30valve Offline


Registered: 03/20/11
Posts: 76
Loc: Michigan
Originally Posted By: gvken
I have 4 qts of Castrol Syntec 5w40, by car takes 8 qts. Is it safe to mix brands of the same weight? Say 4 qts of Syntec and 4 qts of Penzoil Ultra of the same weight?

Can't find Syntec anymore since they switched to Castrol Edge....


RT6 would be a better choice than the Syntec 5w-40. Nothing wrong with the Syntec, but RT6 is generally cheaper and a better oil. Even better would be GC or M1 0w-40, both of which are actually true syn and same price as the 5w-40.
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#2379677 - 09/17/11 08:37 AM Re: Mixing brands - same weight [Re: gvken]
dparm Offline


Registered: 04/19/10
Posts: 12957
Loc: Chicago, IL
If you can get more of the Pennzoil Ultra, it's a better oil than Syntec 5w40.
_________________________
2011 BMW M3 sedan ZCP

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#2381554 - 09/19/11 11:08 AM Re: Mixing brands - same weight [Re: dparm]
gvken Offline


Registered: 08/24/11
Posts: 2
Loc: CA
Thanks for all the feedback.

Maybe I'll just mix with Edge for this oil change, and switch brands on the next.


Edited by gvken (09/19/11 11:20 AM)

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