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1967 Mustang coupe
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Discussion Starter #1
So it turns out that 10W30 dead dinos is hard to come by locally where I now am, they only have 15W40. They have a good stock of synthetic. So I got 5W30 synth.
But then I was reading about mixing the 2 for cost reasons and I got to thinking I could mix synthetic 5W30 with 15W40 dead dinos. Or maybe 5W20 with 15W40. That otta even out to about 30 weight, no?

Are there rules in this game? And sources for proper reading would be helpful if ya have 'em.

DrC

Edit: if you're asking why I'd mix... it's the seepage and leaks... finally got leak free just last week...
 

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68 Mustang Coupe
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Run the 5w30, just a bit thinner in winter time.
 

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Strange, I was at AutoZone yesterday and they had gallons of it.
 

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If you Google it you will find that Amzoil says there is no danger in mixing, only that the performance of the synthetic will be reduced. Unless you are breaking in a flat tappet cam, I have resolved myself to the fact that synthetic is the way to go even if zinc is a bit lower.
 

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I have been schooled that you can mix brands of the same weight, but not different weights of any brand. I would just change the oil and filter to have consistency. It doesn't cost that much.
 
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Working A/M like I did for so many years ,I would say pick a brand and stick to it,mix if you need (or want) to but the science if getting to 10w30 by doing that is not capable without a test lab .

I have been schooled that you can mix brands of the same weight, but not different weights of any brand. I would just change the oil and filter to have consistency. It doesn't cost that much.
The different additives each company uses rule that out for me----pick one brand and stay with it.
 

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Yes you “can” mix the different oils, but the “should you ?” Is more problematic. If one does not have any alternative I would not hesitate to mix synthetic and dino oils . You won’t damage the engine, but won’t be fully taking advantage the the synthetic benefits either.

I’d prefer to just take the small financial hit and do the complete oil and filter change.

Z
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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Over here even the dealerships offer "synthetic blend" which basically regular oil and synthetic. Basically the two mix like they are no different. As for the weights, that's getting pretty deep. But as your car should be happy enough with either, it will be happy with a mix too.

I've used 15W-40 as a warm weather oil for years and years and 10w-30 for cooler weather though lately I've been moving all the cars to synthetic with Mobil 1 5W-40.
 

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The only thing I question about the synthetic “blends” is the lack of disclosure on the label. Are they 5% synthetic / 95% dino or 50/50 or whatever.
I think the whole blend scenario is a marketing gimmick designed to snare folks who want to save some money / or are too cheap to pony up for the cost of full synthetic oil.

Z
 

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I have been schooled that you can mix brands of the same weight, but not different weights of any brand. I would just change the oil and filter to have consistency. It doesn't cost that much.
you can mix oils of different weights, as well as synthetic or dino, or even blended oils.
 

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1967 Mustang coupe
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Discussion Starter #12
I find the cost of the synthetic to be high, but not prohibitive. It stretches out the oil changes anyway. For me it's more about leaks and drips. Pretty much everyone I've seen talk about the swap says they got drips afterwards. Some had it go away, some didnt.
I'm doing my best to have no drips at all =)

My engine seems happy with 30 weight. That's all there is to the goal of XW30. I am considering trying 20 for the hellavit... but that's a another story.
 

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Back many years ago in my teens and early twenties when money was tight I used drippings from my corner gas station. They were the ultimate “blend”
Anyone remember what drippings were?
 
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You can mix oil. The worst effects are that your brain will jell if you over-think it. I recently bought a car that uses 5w-20 oil. I have a couple of quarts of 5w-30. I plan to top up the car with the 5w-30 as it needs it.
 

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1967 Mustang coupe
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Discussion Starter #16
Ahhhh... le Zone Voiture... uh lala =)
It's the emissions... that makes sense. Well, from the looks of it, y'all are tellin me to not stress out about it.
So I guess I'll chill. Synth mix it is. Hopefully there will be enough dino juice to keep er from drippin.
 

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1967 Mustang Convertible
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Only question I have is if you are still running a flat tappet cam, you still have to worry about having enough Zinc in the oil? Mix matching and so forth, thats the only thing I would worry about is having enough Zinc for that cam and lifters.
 

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Mixing oil to get a wt is straight forward.
The Europeans also lead the way on displacing ZDDP, using moly-b and boron.
If info and resources are lacking for an old American car find out what local Porsche owners, from about 1998 and older, find what they are happy with and you should be safe following suit. Same for mid 80's on back BMWs.
 

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Synthetic oil does not cause leaks. It is not "thinner" or more "slippery" or anything else. It is actually oil. These are old myths that never seem to die.
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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Synthetic oil does not cause leaks.
People keep telling me that. Yet I personally have a Mitsubishi engine pouring all kinds of 10W30 Mobil 1 out the cam seals and valve covers after I treated it to synthetic after (I suppose) a lifetime of getting the cheapest oil available.
Not going to argue fact but I will say I bought it with a bad transmission like two years ago. Pulled and rebuilt the transmission and then used it for a backup driver. And it never a leaked a drop until I (eventually) changed the oil for Mobil 1.

Bone dry and clean. Changed to Mobil 1 and come a flood. If it wasn't because of the oil change, then what should I blame it on I wonder?

I'd say it's rare that a swap to synthetic causes problems and the great majority don't have issues. But after almost 40 years of working on cars I like to think I can tell when an engine is leaking or not.
 
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