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Yes, I know it's an oil thread, but this one is a bit different.

I find myself with 3 quarts of Redline 10w40 and 3 of Amsoil 20w40. I know people have had good results with both of these oils, but I'm wondering if there would be negative results in mixing them together. I don't really want to spend $50 more in getting 3 more quarts of Redline to do an oil change.

I know back in the dino juice days we were always told not to mix Pennsylvania and Texas oils. Don't know if that would apply to full synthetics, or even if it was a real issue in the first place.

Your thoughts/info on this is appreciated.
 

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It is a requirement today that oils are compatible for mixing. It should not be a problem. Both those oils have mostly PAO in them with some ester and some Gp III between the two.
 

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This thread reminds me of the old Fram oil filter commercials........”you can pay me now, or you can pay me later!”
 

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I too have mixed reg oil with the Synthetic stuff and never had any issues.The last bike I owned [a 2010 Triumph Thunderbird 1600] called for synthetic oil "ONLY" ,just like our Indians do [actually,it's a semi synthetic oil that the Indian motor uses],which I did use for the first 10,000 miles I drove it.However,on hot days,especially when in stop and go traffic,that motor sounded like it was gonna give birth as you could hear every moving part inside the motor thrashing away.So,knowing this condition was not doing the motor any good,I tried mixing some regular motor oil with the synthetic stuff,attempting to quiet it down,but the motor still made some noise.So I changed it to a conventional,non synthetic oil,more specifically, Shell's Rotella T 15/40 which is used in diesel motors,and never looked back as the motor now ran quiet and was still quiet when I traded it [at 125,000 miles] for my new Springfield Dark Horse.

So armed with that knowledge,on my first oil change,two days ago,at the 500 mile mark,I went right to that same non synthetic oil,just like I used in my Tbird, and the motor has already quieted down somewhat compared to what it sounded like before.So I'm gonna use it for awhile and see what happens.Dave!!!
 

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I'm 99% sure the old "don't mix oils" idea was based on the detergent, non-detergent oils that were around up into at least the 70s and maybe even the 80s.

The general rule was that if you had an engine that had been running (during its life) with a detergent oil that you could add a non-detergent oil and things would be okay.

The difference was merely based on price, detergent oils were more expensive when they came out and I'm sure there were folks who claimed that in some way a non-detergent oil still had some superior capability.

So, if you had an engine that had been running (during its life) on non-detergent oil the rule was that you should not add or use a detergent oil.

The original motor oils were non-detergent (just good old oil) and sludge would build up in the small nooks and crannies inside an engine. The sludge would stay there and not really be a problem. But it would obviously be better to not have any sludge build-up and so that is why they developed detergent oils.

Detergent oils (new higher tech oils) were such that they would either not allow this sludge to build up (I imagine by keeping the particles in suspension etc.) or minimize it building up.

If you put a detergent oil in an engine that had been running non-detegent oil *all* of the sludge would be quickly loosened and put into suspension in the oil and it would be like shit running through your motor.

(if you know how modern washing machine detergents work, they are using a lot of the same principles, they get things to loosen up that you could not get loose (stains) 20 years ago)

So, the only issue these days would be doing something like putting a 10-30 oil into a motor which is running a 40 straight weight. That would not be good but it actually probably would not do anything bad as the current oils are light years ahead of what was available prior to the 80s.

Most engines run much higher oil pressure now vs. the old engines where mixed weights might be an issue.

(but I do remember that some oils had a higher sulphur content and maybe that also had some play in the "oil rules" (Texas vs. Penn etc.).

I doubt there is any oil sold that is non-detergent (but I don't know for sure).

HTH.

WD./

And if you talk to a real old-timer he will tell you that castor oil was the best racing oil ever. But turns out that if you did not drain it out while it was hot (after the last race of the day) it would set up inside your engine and you were hosed (have'ta do a teardown to get it out). And yes, that's where the Castrol brand name came from.
 

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One issue that is fairly rare, but does happen, is that oil can gel. I have had to deal with this nightmare before on diesel engines. Once this happens, you are in for an expensive complete overhaul and the mechanics will not be happy with the job either. That stuff can be near impossible to dissolve without very aggressive solvents. Why it happens? Some have suggested that incompatible additives are a factor. For my 2 cents worth, I would never mix oils except in cases where I had no choice or didn't much care about the possible risk.
 

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I would never mix oils except in cases where I had no choice
I had to do this once on a trip. Needless to say, the oil got changed as soon as I got home. But I couldn't see any ill effects and I thought I would. Mixed Redline 20/50w with straight 30w in Arizona headed back to northern California. Maybe I just got lucky too. That's always a possible. But it was a full quart. What bothered me more was where the heck the quart went. I changed oil before the trip and I'll swear it was at the correct level when I left. But checked one morning before heading out and it was down a full quart. Never happen again and that bike had 66k miles when I sold it 2 years later. That one case still bugs me to this day. Guess it shouldn't but it does.
 

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Chemicaly, no issue whatsoever. The one cosnideration is that the Vis will not be spot on 20W40 (you'll be close to 15W40). Probably not a huge deal, but something to keep in mind.

Any modern (last 20 years) synthetic motor oil is compatible with any other available on the market. Ride Safe- John
 
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