Mixing synthetic oil and conventional oil

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smlobx

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I'll also jump on the Mobil 1 bandwagon!

It is specified for our Porsche and I've used it in all our gas engines.

I run Shell Rotella T6 5W-40 in the Jeep EcoDiesel and my F-350 diesel as well as our construction equipment and have never had an issue in over 30 years...
 

Temudjin

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Another issue you need to be aware of is that modern engine oil is not just oil - oils use many and varied additives to achieve specific ends. Detergents are used to remove contaminants from engine components but there are many other additives that help maintain viscosity over the life of the oil, and yet others that help the oil deal with extreme heat and/or cold and lots of other things.

When you mix different brands of oil or even different types of oil from the same manufacturer you risk the various additives working against each other and the oil delivering less than optimal protection.

The science behind modern lubes is almost "rocket science" and unless you really know what you are doing I think it's better to follow the expert's recommendations.
 

BLACK_BETTY

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The only reason I would mix them is in an emergency. There are way too many variables to be certain. Sure there have been semi-synthetics for years but they were formulated that way. One variable with your setup will completely change the oil.

Now that being said, I work in an oil refinery with massive rotating equipment. Said equipment runs 24/7/365, some for years at a time without shutting down. We recently started upgrading all our lube oil to royal purple. In the equipment that could be shut down, it was swapped out completely but reservoirs were not cleaned or anything. On equipment that couldn't be shut down, we would drain a barrel of the old and add a barrel of the new, one at a time, until our rotating engineers thought the ratio of old to new was sufficient and said to stop. Keep in mind, some of the crankcases on our bigger equipment hold 12+ BARRELS of oil.

I have also read of people mixing their own but I have a hard time overriding the engineering behind multimillion/billion dollar corporations.
 

Sonarman

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Watch Project Farm on YouTube and see the oils he tests. Pretty amazing test he does, excellent video. Not just oils but he tests glues, duct tape, bed liners. Myself I run Amsoil 100 percent synthetic which has been in my vehicles since 1976, when it wasn’t cool to run synthetics. Everyone would say it would leak out and wreck the seals.
Then Mobil 1 came along and it was suddenly it was cool stuff.
 

Desert Runner

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If the only disadvantage of mixing mineral based and synthetic is that it drops to the lowest common denominator of protection (crude based), then why are we buying semi synthetic? Do they really do something in in the mix to make it better than just crude based? Sounds like a marketing gimmick to me.
Revisiting this:

I think 'blending' would not be detrimental, except as stated above, as long it is kept in the family. AKA...... Same Brand, same or similar ''ADDITIVES', as that determines how well or not, it will work.
 

mv213

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It’s amazing how long the old wives tales stick around. Every time a newer technology comes along there’s a new “old wives tale” to go with it. There are several about synthetic oils, mentioned above, all false of course. There was another one that if you switched an older engine to synthetic you would “make it leak”. Never mind that an older engine most likely leaked already or was only sealed because of the sludge buildup. There were a few about radial tires, alternators, disc brakes.....
 
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4Corners4Runner

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It’s amazing how long the old wives tales stick around. Every time a newer technology comes along there’s a new “old wives tale” to go with it. There are several about synthetic oils, mentioned above, all false of course. There was another one that if you switched an older engine to synthetic you would “make it leak”. Never mind that an older engine most likely leaked already or was only sealed because of the sludge buildup. There were a few about radial tires, alternators, disc brakes.....
I remember our transition from carburetors to fuel injection, even though fuel injection had been around years and years, back in the seventies and early eighties stopping at 9500 ft to change jets in our carburetors!
 

smritte

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I just attended a seminar put on by Mobil. I'll just add this, according to the engineers from Mobil, there is no "standard rule" for semi synthetic. In other words, if you take regular non synthetic and add 1% synthetic, you can sell it as "semi". The guy pretty much said, don't waist your money on it.
As everyone posted, it really doesn't matter which you choose as long as you change it on time. I periodically send out an oil sample and have it analyzed ( I use Blackstone labs). The results will tell me state of the engine and how the oil is holding up. I learned that in my Tacoma I was changing it way too often and my TJ not enough.