Mixing 2 oil brands safe?

Doing oil change, I have 5 quarts of Yanmar 15w40, and the rest is Rotella 15w40....is it ok to mix the two . Or stick to same brand .?

My understanding of oil is keeping the same weight and viscosity is fine - both are 15W40.

agreed on weight, oil change warm or cold what is better choice to get as much out as possible?

So the way my dad taught me is cold allows the oil to drip back in the pan. Otherwise warm or hot the oil is going to be in and around the engine and less will be in the pan.

Chemically the additive packages may be different and not compatible.There is no upside to mixing oils. Why do it on a newer engine especially a Yanmar with a storied history on valve failures?

What diesel engine oils does your local Yanmar dealer or book recommend? Your engine has some engine specific metallurgical components. "It's OK" from an old Lehman or Perkins perspective may not be correct.

"Probably" OK to mix oil brands. There is a fair chance that the Yanmar oil is just repackaged Rotella. Yanmar does not make their own oil, they buy it from some supplier.

But the question is how compatible the two additive packs are. 99% sure they are compatible. But for $20 worth of oil, why even think about it?

I often end up with random bottles of oil from old engine room stores. I keep it in my shop for lawnmowers, oil cans, chainsaw bar oil, flushing out sunk engines, etc. None goes to waste. But I don't mix oil brands on purpose.

Best to change oil with engine warmed up. It is a pain to suck out cold thick oil. I've burned up an oil change pump trying to do that.

My theory is that there is an unknown oil in there right now. And I'm probably not getting all the oil completely out on the drain, so when I fill with new oil there is going to be somewhat of a blend to start.

Then go ahead and use it. It will "probably" be just fine.

It may be best to figure out how to get "all" of the oil out. Once our setup gets "all" possible out I add 2 quarts of new oil and pump it out too, call it flushing if you will. Yes, it costs me an extra $13 dollars a year for two engines.

If you don't know what's in there now, you will probably be mixing brands of oil to a certain extent. However, if you stick with a single brand of oil, your oil will get more "pure" with each oil change.

Personally, I would use the Rotella and sell the other oil.

SILENTNIGHT,

What’s the downside of getting all one kind of oil? A trip to the store? Then do it.

I avoid mixing brands re the additive issue but at times mix viscosities. Like in the summer keep mostly 30w but include a quart or two of 40w.

Re the re-branding I’d guess it’s most likely Valvoline. NAPPA oil is valvoline.

Re this question there is very little down-side .. but it’s there.

I seriously doubt there's any down side these days...as long as they are quality name brand oils. It was probably very different way back in the day maybe 50 years ago or more, but now these oils are all produced to industry standards.

It's been 30 years ago now, but as a young engineer I worked in a papermill and used to work with lubrication engineers from Texaco quite often. I remember having conversations with them about these sorts of things and as I recall it wasn't such a bad thing even then to mix....

It's been too long for me to recall anything about the specs or standards though....

I'm sure you'll be fine.


I wouldn't do it though.

https://www.valvoline.com/about-us/faq/general-motor-oil-myths



MYTH: Switching motor oil brands is harmful to my engine.
No. Switching brands is not harmful to your engine as long as you choose an oil marked with the API donut of the same level, e.g., API SN. Motor oil manufacturers must meet minimum industry standards for performance and compatibility of the API mark. However, make sure you follow the recommendations provided in your owner's manual for viscosity and API category. You may give up enhanced performance if you switch from synthetic or high mileage to conventional oil.

My voice of reason said use the same oil Rotella 15w40.
I have 2 dip sticks a small one and a long one?
The long one shows all way to full, the short one 3/4 ? Which one is accurate.

Engine might lean a bit to one side or the other from install or boat loading, so it is common for sticks to read a bit different. Don't worry about it, oil level is fine if both sticks are in range.

Gradually use up the 5-qts Yanmar oil in your generator (assuming you have one)?

-Chris

I would say "Go for it". Think about when you add a quart of oil to your car. Unless you do your own oil changes you probably don't even know the brand of the oil in the engine. You probably think you know the viscosity but maybe not. You just add a quart of whatever is available. At least I do.

BTW, I have 250,000 miles on my Volvo (car) Still runs great. When it needs an oil change I just take it in,I have no idea of the brand of oil in it.

pete

SILENTKNIGHT said:

My voice of reason said use the same oil Rotella 15w40.
I have 2 dip sticks a small one and a long one?
The long one shows all way to full, the short one 3/4 ? Which one is accurate.

Click to expand...

Drain the engine as completely as you can. Then fill it with the correct amount of oil. Check the level with both dipsticks. Which ever one shows it being filled to the proper level is the one to use. If neither one shows correctly then remark one to show full and go with that one.

In an emergency, it really doesn't matter. When you get back to shore, change the oil.
Way way back in time, the brand may have made a difference. Now, with the govt and industry standard printed on the labels pretty much tells us what to match.
Single or multi-weight oil..... use the recommendations of the engine manufacture.
I personally like the single weight oils.
Of course if you operated primarily in the frozen north, multi-grade oil might be better, especially if the engine is shutdown for a long period of time. Once everything gets cold, it will be difficult to spin the engine fast enough to get it started.
It has been said repeatedly, never, never, never use starting fluid. I know of an Oliver tractor engine that would not start below 10F without a shot or 2 of starting fluid. I suspect that engine is still running in the same tractor and that was over 30 years ago.
I did have a neighbor who would rebuild, as necessary, some hit and miss tractor engine. Start on gasoline and then with a flick of a valve, changes to running on diesel fuel.

Look at the specs on the back of the container. If the both meet the same manufacturer specs your good. Ya mar doesn’t make oil

Lubricants are blended to specific requirements. As long as the oil meets the OEM requirements, it is fine.

Crude oil is organic and varies greatly as it enters the refining and distillation processes. The blending and additive process compensates to build qualities that adhere to the specific standard (there are hundreds if not thousands of different lubricant standards),. The goal is to make a homogenous and fungible product that adheres to lubricant specifications specified by the OEM.

Bottom line is it simply is not possible for two batches of lubricants from different refineries or producers that meet the same standard to be incompatible. One may have slightly different additives, but they must both meet the same standards.

Let's face it. That's the goal of a standard. To suggest that two products that meet the same standard are incompatible is just incorrect.

Peter

mvweebles said:

Lubricants are blended to specific requirements. As long as the oil meets the OEM requirements, it is fine.

Crude oil is organic and varies greatly as it enters the refining and distillation processes. The blending and additive process compensates to build qualities that adhere to the specific standard (there are hundreds if not thousands of different lubricant standards),. The goal is to make a homogenous and fungible product that adheres to lubricant specifications specified by the OEM.

Bottom line is it simply is not possible for two batches of lubricants from different refineries or producers that meet the same standard to be incompatible. One may have slightly different additives, but they must both meet the same standards.

Let's face it. That's the goal of a standard. To suggest that two products that meet the same standard are incompatible is just incorrect.

Peter

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This! Oil is a religion for so many people. I see it on car and truck forums, heavy equipment forums and, of course, boat forums. Oil company marketing is working well or people are afraid of all things mechanical so particularly in when it comes to engine oil, they go with more dollars must be better. Yet, no one is ever able to produce evidence of an oil failure that is purely related to running a "cheaper" oil.

As you state, their cannot be major differences in the additive packages or the oils would stray from the standard.

lube oil as a "religion".... and cheap oil
As a teen many years ago, when I was more 'into' cars, working on them, friends with hotrods, etc.... I developed a theory about 'cheap' oil....particularly Quaker State Oil. (is that stuff still sold?)

Theory - people that 'add a quart' will tend to buy cheap
and it's the adding a quart that becomes the problem...not the cheap oil


So I figured that folks that go cheap on their oil are more likely to just generally not care so much about babying their cars...and by extension are much less likely to do regular oil changes, etc....
or a parallel could be folks that have cars that were not in the best condition...burned oil....
and so adding a quart becomes routine.

Extended time between changes leads to greater evaporation of the short polymer chains leaving more long ones....sludge...dirt build up...etc....


I developed the theory, I think after working on my mom's Olds Cutlas Salon..changing the lifters and cleaning up the 350.... that had many times had a quart of Quaker State added to top it up.....

Had to post after reading about Quaker State

As a youngster I remember having a conversation with a petroleum engineer as he filled his car at a discount gas station. He said if it burns, buy the cheapest thing available. If it lubricates, buy any name brand lubricate and never change brands. Crude from different parts of the world are in fact not particularly compatible, and when combined with different cracking methods and additives, may not play well with each other to the point that one may have to be completely worn from a bearing surface before the second will move in to lubricate.
So for years I used Quaker State 10w-30 in a '68 mustang, even after later hearing disparaging remarks about Quaker State. At around 150,000 miles I was involved in a accident on I-95. The insurance company decreed the car to be totaled, and I bought it back from them to drive until my new vehicle shipped. Bottom line, my neighbor, jet engine mechanic for Eastern Airlines, wanted the engine for a race car. His plan was to rebuild the lower unit and add some racing components. He told me after dropping the pan that it looked brand new, and there was no reason to do anything.
Just my experience, your mileage may vary.

skyhawk said:

lube oil as a "religion".... and cheap oil
As a teen many years ago, when I was more 'into' cars, working on them, friends with hotrods, etc.... I developed a theory about 'cheap' oil....particularly Quaker State Oil. (is that stuff still sold?)

Theory - people that 'add a quart' will tend to buy cheap
and it's the adding a quart that becomes the problem...not the cheap oil


So I figured that folks that go cheap on their oil are more likely to just generally not care so much about babying their cars...and by extension are much less likely to do regular oil changes, etc....
or a parallel could be folks that have cars that were not in the best condition...burned oil....
and so adding a quart becomes routine.

Extended time between changes leads to greater evaporation of the short polymer chains leaving more long ones....sludge...dirt build up...etc....


I developed the theory, I think after working on my mom's Olds Cutlas Salon..changing the lifters and cleaning up the 350.... that had many times had a quart of Quaker State added to top it up.....

Click to expand...

Quaker State used to have a bad reputation because it had a lot of paraffin in it and people would get waxy build-up and clog oil passages. That is long since in the past.

Quite frankly, I'd rather buy an engine from someone who bought cheap oil and changed it and filters frequently than someone who bought the most expensive stuff and thought they could go 20,000 miles on. Different versions of cheapskates, so you can't be too sure either way.

Read the labels, if they say both are "Mil Spec" followed by numbers and/or letters it means they are both authorized as being interchangeable for military vehicles. It is nonsense that one or the other will wreck you engine is just that, nonsense.