How beneficial is mixing GC with regular Syntec?

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28
Location
Iowa
I got a great deal on 5w30 Syntec ($1.66/quart) on closeout. Bought 12 cases (72 quarts) of it, thinking it would last for the rest of the life of my 1998 V6 Accord (120K miles) and be usable on most any other vehicle I would own down the road. Even though I didn't buy it from AZ, they were nice enough to swap 6 quarts for the 0w30 GC that they alone seem to carry. I currently don't drive more than 8K miles a year. OCI in owner's manual is 7.5K in normal conditions, but I do a change with the summer/winter seasons, so usually no more than 7 months and 5K miles on a fill. Car has a rear main seal leak, used to be to the tune of 1 quart every 2K miles on Mobil 1. I switched to Formula Shell (Costco had for $2/quart), thinking if I was losing oil, I didn't want to spend money on the synthetic stuff. That was 2 years ago. Now the seal has significantly diminished in leakage, though it's still present. I figured, since the Syntec is Group III, it shouldn't have any more of a predeliction to leak than the dino. My question is, since I was able to get some GC, would I be better served mixing in a quart of GC with the Syntec, or should I just stick with 100% of either when filling? Car holds 4.5 quarts or so, so it'd be like a 22%/78% mix of PAO and Group III.
 
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39,806
Location
Great Lakes
I'd be a waste of perfectly good GC, but other than that, no harm done I suppose. :) Also, if I counted right, this oil will last you for 8 years. Not sure that I'd want to pour 8-year-old oil into my crank case...
 

speedbump47

Thread starter
Messages
28
Location
Iowa
So, in your opinion, adding it wouldn't be enough of an improvement to merit using the GC? Just use dedicated fills...maybe leaving the GC in for a full year? I thought of the shelf life thing too, and many people (Mobil included) say that 5 years is the lifespan, while I haven't seen complaints about even longer. There's even a thread on here dedicated to oldest oil used. I figured, with proper storage, it should hit at least that. Come 5 years, all the while oil getting to be more expensive (inflation and the like), if I have to trash it, I won't be too sad since I got it at $1.66/quart. Plus, hopefully it'll be usable in any other car(s) I might get down the road before it "expires".
 
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5,628
Location
London, ON, Canada
Even if it passes 5 years, I'd use it in older cars, if you had a beater or something, and small engines and things like that for sure. I wouldnt worry about its shelf life that much.
 
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11,247
Location
PA
Don't worry, you'll use it or give to a friend. Hang on to the GC, you'll use it eventually. Don't mix it. Try it inthe Accord in summer, if you want.
 
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1,648
Location
Little Rock, AR
There's a guy with a Sienna in the UOA section - he was mixing Pennz. YB with PP - and his TBN value was very low in just around 4k or so. The consensus was, stop mixing. (I'm mixing in my Sienna as well - using up left over PP - but I now plan to stop the practice). It may have nothing to do with his low TBN, but otherwise no one could figure it out. Probably silly, but I'm now spooked on the practice.
 
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782
Location
Alberta
 Originally Posted By: ericthepig
There's a guy with a Sienna in the UOA section - he was mixing Pennz. YB with PP - and his TBN value was very low in just around 4k or so. The consensus was, stop mixing. (I'm mixing in my Sienna as well - using up left over PP - but I now plan to stop the practice). It may have nothing to do with his low TBN, but otherwise no one could figure it out. Probably silly, but I'm now spooked on the practice.
Don't pull the fire alarm on mixing oils yet. ;\) I just checked some UOA's for the Sienna engine, and it really trashes oils -- especially the TBN. See my post in that thread … link
 
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595
Location
Hither & Yon
Speedbump, I posed essentially the same question to Castrol USA representatives. After carefully reading the label on the Castrol Edge bottle, I still could not determine whether it was "permissible" to mix Edge with Syntec or even conventional GTX. (More specifically, a Syntec bottle says it is fully compatible with a laundry list of other oils; the Edge bottle doesn't.) The response I got (long since deleted or I'd attach it here) reads, in part, as follows: "All Castrol motor oils are fully compatible with one another, and there is no cause for concern if you switch from conventional to synthetic or vise versa, or choose to mix one type of Castrol motor oil (conventional or synthetic) with another." (Emphasis added.) The company further stated, "There also is no harm in switching brands of engine oil so long as you follow the guidelines of the manufacturer for grade and API performance specific to your vehicle's engine." Consequently, IMHO, you can mix and match Castrol motor oils to your heart's content. Doing so may, of course, reduce or dilute a particular property of the "better" synthetic, but there's no reason to think you're going end up with a hybrid that's somehow less effective than the lesser of the two synthetics.
 

speedbump47

Thread starter
Messages
28
Location
Iowa
Thanks for the replies guys. One other reason I wanted to mix a bit was that the cSt for 5w30 is 9.7 (pretty thin for a 30 weight) and 12.5 for GC (nearly 40 weight). Figured throwing in a quart of GC would help bring the entire fill to 10+ cSt level. Sounds like there will be no detriment to mixing, other than perhaps diluting GC's benefits (though marginally improving the fill as a whole). That's palatable.
 
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39,806
Location
Great Lakes
 Originally Posted By: mshuell
Inquiring minds want to know. What happens to oil when it sits unopened in the can for eight years?
Good question. Some oil companies seem to think 5 years is max, but they don't give a reason why: http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/Mobil1_Shelf_Life.aspx I think the main reason for me would be the advances in technology. Look how far motor oil has come in the past 10 years or so. Would I want to use some old technology in my car if better oil is available? If we're talking about an old beater, I guess it's fine. But a lot can happen in 8 years... his Honda might get totalled. He may end up buying a different car that requires different type of oil, etc. That's why I don't typically stock up on oil or filters... it's not like there's an oil shortage out there, and it's not like a need for an oil change is going to catch me by surprise... Plus, my better half might start getting suspicious if she sees 72 quarts of oil in the garage... :) I fully understand his price incentive, though.
 

speedbump47

Thread starter
Messages
28
Location
Iowa
Yup, I think the major arguments lie along the lines of obsolescence (vs. expiration/degradation) and getting locked into a specific grade. The low price was the big deciding factor (even at $3/quart, I wouldn't have bought more than 24 quarts), and while I can't predict what will happen with the car, I'm not so concerned with a huge breakthrough happening and making the oil not worthwhile to use in the car. I think a decade of improvements (past when the car was made), is enough for me; something 5 years down the line isn't likely to create a paradigm shift for my application. And, sadly, I have no better half yet to disapprove.
 
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