Switching between oils of completely different chemistry

[Javed]

What negative can happen? And would you even bother to do a UOA because the oil sample will not be 100% of the same oil? For example, you switch from PUP 5W30 to HPL SUPER CAR 0W20. As far as and as little as I know, those two are very different oils.
Thank you

 

[Jetronic]

It might mean the blend will not perform to any standard either of the 2 oils meets. Then again, it just might.

 

[wemay]

It might mean the blend will not perform to any standard either of the 2 oils meets. Then again, it just might.

I understood the question to be about switching between oils after an interval run, not mixing or blending. In which case I'd posit, no issues at all.

 

[Jetronic]

I understood the question to be about switching between oils after an interval run, not mixing or blending. In which case I'd posit, no issues at all.

Well, I understood the same, and also say no issues at all. But the first fill after switching, might not perform like the old oil did, or how the new oil will in subsequent fills.

But there's plenty of people who use a different oil at every change and they have no issues either.

 

[rstcso]

This thread has a perfect example of what happens as you're switching from one oil to another. This was my comments in the thread:

"Oil Analyzers' results perfectly illustrate the importance of running an OCI between changing brands and/or blends of oils. Sample #3 is basically a blend of the HPL virgin sample #1 and the M1 from sample #2. Not until sample #4 do the results start looking like virgin sample #1."

 

[cptbarkey]

Oil is oil.

One oil that has different elements would be Delo ADF.

 

[rstcso]

But there's plenty of people who use a different oil at every change and they have no issues either.

No immediate issues. There is no way to know the long-term effects. They may only get 300k miles vs 302k miles from their engine.

 

[Jetronic]

No immediate issues. There is no way to know the long-term effects. They may only get 300k miles vs 302k miles from their engine.

they might need to use VRP at some point, nobody knows.....

 

[rstcso]

they might need to use VRP at some point, nobody knows.....

Three. Three is the correct answer... at least that's what The Wise Old Owl says.

 

[AEHaas]

While oils may be "compatible" and mix well they may not perform as intended. Let's look at a 50-50 mix of two different oils:

Oils may be formulated with very different VII, viscosity index improvers. After the mix there is only a 50 percent level of each type of VII. It may or may not work out to give you the intended final viscosity and range at temperature. Some oils have a lot of VII and some have none at all in their formulation.

There are newer oils that do not have any ZDDP. Other additives take its place. A mix will dilute both types of additives 50 percent. Is that enough of either to do the job?

In general many engine oil changes result in residual levels of 10 - 20 percent of the previous oil. I would run only a very short interval if I used a very differently formulated oil. In the "old days" oils were very similar. Today they can be very different.

Some in the industry say to pick an oil and stick with it for the life of the car, better in the long run. Does it really make that much difference? Maybe not but the purist would care.

Ali

 

[dnewton3]

I'm going to take the OPs question at face value; what is the potential for problems when swapping lubes at the OCI?
The reality is there's not a lot of risk in terms of actual wear protection, but there will be some potential for odd readings in a UOA.

**************************

I'm going to add some info which is related, but not directly to the OPs question:
What happens when you mix lubes intentionally in one sump load ... 2 qrts this and 4 qrts that, as an example.

For most API approved lubes, there won't be any real negatives in terms of performance or wear protection when mixing lubes. API lubes are generally already a compromise of many facets, so mixing them isn't going to lessen the outcome much, if any. One can certainly lose some potential if you'd change from a nice group IV to a II+ in terms of oxidation resistance for example, but overall if the OCI isn't too long, it would not really manifest into a problem for the equipment.

However for some boutique lubes (HPL, Amsoil, etc) which are highly specialized, crafted to a edge of some chemistry envelope, there is a potential to upset some balance and lose the "best" functions of the lube. That doesn't mean the lube will just degrade and become worthless, but it does mean that the attributes sought might be compromised to X% degree if diluted with a competing chemistry. Some specialized components such as anti-foam additives are one such example; too much of a good thing becomes a bad thing very quickly. Same goes for ZDDP; too much zinc can become corrosive. This is why mixing lubes of competing chemistry in the sump isn't a good idea. If you're going to switch to a boutique lube, it's best to run the first OCI fairly short and then run another load worthy of taking a UOA.

 

[Ride_Red]

I think the amount of residual oil left in the engine is very much make and model dependent. I let my oil drain and drip quite a while to get as much out as possible. This reduces any effects of dilution or mixing of additives. I refill my Toyota Rav4 with the entire 5qt jug and it's right at or just slightly above the full line, so I'm pretty sure most of the old oil is gone. beyond that, the most a guy can do is a short OCI flush with the new brand of oil, but I'm not doing that.

I've swapped brands and mixed top-up oils in cars and they all went 150K - 200K miles before being sold with good running engines. Will mixing oils cause harm? Hard to tell. I'm sure it could be measured in a controlled test environment, but not in my driveway. My mower has lived on a frankenbrew of drip oil for 20 years from all the open bottles of various brands and grades of car, diesel and motorcycle oils I've had pass through my garage. It's still running great.

 

[rstcso]

This is the response from everybody's favorite Motor Oil Geek in my quest to find "the best" oil. He suggests running a 3k-4k interval to flush and not take a sample for UOA until after the subsequent OCI.

"...try a different brand of oil in the same viscosity grade of whichever oil had the lowest wear rate per 1,000 miles. You will need to use it for 3,000 to 4,000 miles to flush the OEM oil out of the system before going 5,000 miles on the new oil to take another sample..."

 

[factorytuned2012]

What negative can happen? And would you even bother to do a UOA because the oil sample will not be 100% of the same oil? For example, you switch from PUP 5W30 to HPL SUPER CAR 0W20. As far as and as little as I know, those two are very different oils.
Thank you

Never something that ever crossed my mind not enough residual left behind to think about this.

 

[rstcso]

Never something that ever crossed my mind not enough residual left behind to think about this.

You'd be surprised. Go to the link in post #5 and look at what happened when they went from one oil to another.

The difference results when I switched from OEM to Amsoil aren't quite as dramatic, but certainly paints a picture of the two oils blending. Especially notice the viscosity difference between the virgin sample on the right and first sample after running it 4k miles with having 500 miles on the OEM oil. Also has more moly than the virgin sample.

 

[userfriendly]

This is the response from everybody's favorite Motor Oil Geek in my quest to find "the best" oil. He suggests running a 3k-4k interval to flush and not take a sample for UOA until after the subsequent OCI.

"...try a different brand of oil in the same viscosity grade of whichever oil had the lowest wear rate per 1,000 miles. You will need to use it for 3,000 to 4,000 miles to flush the OEM oil out of the system before going 5,000 miles on the new oil to take another sample..."

The Geek bases his wear rates on three dyno pulls on a 70 year old engine design.

 

[rstcso]

The Geek bases his wear rates on three dyno pulls on a 70 year old engine design.

How does wear rate have any correlation to engine flush recommendations when changing between brands of oil?

I'm not saying his YouTube videos aren't loaded with questionable statements. Just saying your statement isn't relevant to the OP.

 

[factorytuned2012]

For everyday transportation there’s no way of reason to be a concern I switch oil brands all the time they are GF-6 oils big deal if there’s clashing of additive packs from one brand of oil to the next.

 

[altaylar]

It might mean the blend will not perform to any standard either of the 2 oils meets. Then again, it just might.

Exactly. The chances are it will underperform either of them on the first fill. But with the second fill, the initial oil should be diluted enough that it should not matter.

This is true for most regular passenger cars. My car has an oil cooler that hosts about 20% of the oil which does not drain during an oil change, if you assume another 10% stays in the pan & engine, that means i change only 70% of the oil each time, so with the second fill there would still be 10% of the initial oil remaining.

I know people who mix various oil thinking they are getting best of the both worlds, like esters from PUP and PAO from Mobil 1. Unfortunately it doesnot work like that, this is an optimization of balance problem, not maximization of minimum ingredients problem

 

[Javed]

Exactly. The chances are it will underperform either of them on the first fill. But with the second fill, the initial oil should be diluted enough that it should not matter.

This is true for most regular passenger cars. My car has an oil cooler that hosts about 20% of the oil which does not drain during an oil change, if you assume another 10% stays in the pan & engine, that means i change only 70% of the oil each time, so with the second fill there would still be 10% of the initial oil remaining.

I know people who mix various oil thinking they are getting best of the both worlds, like esters from PUP and PAO from Mobil 1. Unfortunately it doesnot work like that, this is an optimization of balance problem, not maximization of minimum ingredients problem

Thanks for the replies everyone. So the first fill has to be run for like 3000 miles or 20 miles will be enough too?