Mixing oils and adding aditives

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Oct 10, 2017
Northeastern Vermont
Hi guys. There has been a lot of discussion on bitog on adding oil additives like Lubegard and others. Some say it's ok, some say it alters the add pack of the oil. Yet most oil producers like Pennzoil Valvoline and others say their oil can be mixed with any synthetic or conventional oil. Won't that also change the add pack of their oil??. Oil producers i believe also do not recommend additives. There are folks here in bitog that mix different brands of oil and different weight of oil. Is there a difference between mixing oils and adding additives?? Just curious.
Yes. Remember there is always residual motor oil left in the engine after an oil change. Check the Q&A .
None of the oil manufacturers advise to intentionally mix oils. If you check the Q and A's they specifically advise against intentionally doing so The miscibility standards are exactly that...a finished oil is mixed with 7 reference standards, frozen, heated frozen, thawed, and they aren't allowed to blow chunks, or split like salad dressing...that's it...full stop. there is no claim of any rating/specification having been met by the mix, no guarantee of cold start performance, cam wear, any of that. As to the residual oil left in the sump...one of the big published by the SAE issues was exactly that. residual factory fill in a fleet of vehicles didn't play nicely with the first service fill, and a bunch of engines were damaged by pumpability failure at close to normal ambient temps. Extremely rare combination, but it DOES happen. Additives...they are subject to their own testing...not API, so nobody knows what other effects that they have...I mixed some MoS2 additive with a 5W30 and it definitely changed the behaviour at -19C in my freezer.
Nothing wrong with changing brands, weights.....etc, as long as the weights / viscosities are mentioned in your manual. Been blending oil-brands for almost 30 years. I'm talking first & last owner of all my vehicles...... averaging 17-18 years before Michigan's road salt produces massive rust. My engines go to junkyard / graveyards in great shape. Never had to remove the top of any engine to fix oil-related parts. Mix-on and sleep well. Additives for things like consumption and engine noise can help. Every situation - every vehicle is different. Additives require a little ownership chemistry skill. Tinker and experiment with them. Shorten OCIs using additives for repair purposes. I've used CD2 products enough and trust them. They cut down noise and they lowered consumption for me. Brands like Bardahl and STP are not found on my garage parts shelves. They don't seem to work as well for me. I've used Rislone quart bottles (not the concentrate) with success. I've only had success using Marvel Mystery Oil in my gas tank. Usually 4 ounces per 16 gallons of gas will allow me to feel a positive difference in my gas pedal.
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There are a couple of issues presented here. Some of us keep more residual oil in the system at partial change time. We drain the sump, but leave the filter full and in place. This is to keep the AW compounds that the engine has made in effect until the new oil can get into the game. A few weeks later we change the filter and top up. It seems odd, but it is effective according to some of papers notes on BITOG. Others of us have run top flight oils out to 75,000 miles and counting. But only with by-pass filtration and regular UOA's so we actually know what the oil is doing. There is a lot of knowledge here, but it's presented in a spotty fashion ... No refiner could guarantee their oil mixed with any other. How could they? They do not know what you are mixing it with. So you need to be cognizant of what the basic add pak is/was. BUT, on the road and you are a qt low, you will always put in what's available. Some oil is better than no oil - rule one. So is the heat absorption of a full sump more important than possible conflicting add paks. I think so. Other disagree ... Then there is the type of add pak. What will pass Dexos is different from what a boat engine wants or a tractor (gas or diesel). Some add paks may not play as well with others. For additives, all I can say is I use what I know works from many decades of tinkering on engines. That knowledge is not scientific. I sometimes offer it in specific cases here when a question has been asked that I think fits. But I don't get all out of joint if folks do not do as i suggest. They do not live where I live. Their ambient temps are different. Their gasoline is different (ours is controlled by CARB). Their egineis usually different. So my advise may not be helpful. I get that. But I have built my share of engines. 4-stroke and 2-stroke. Been doing this since about 1962, so I have seen some significant changes in oil and add paks. Flathead's to big block Chevys, bikes and chainsaws and a few marine and tractor units tossed in. I've done partials on quite a few marine engines and truck engines. Had more than a handful down the race track (mostly drags, but two roundy round engines also). Only thing I have never wrenched is a aero engine ... I can tell you there is more difference between Aero oil and Marine oil, than between all the API certified over the road use oils. That ought to say something ...
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Certified oils are able to be mixed with other certified oils. It's not ideal but it can be done without causing harm. Additives are really a shot in the dark. It take research and objective thought to achieve any tangible results with off of the shelf additives. At best most additives cause no harm such is the case in the majority of the time.
Mixability was a standard back in the 60s and later IIRC. It was a military requirement for any oil that they purchased for their millions of vehicles. The majority of oils and oil blenders generally use the same or similar additives in varying percentages according to each of their recipes. My 2¢
Quote: "their oil can be mixed with any synthetic or conventional oil". This is an API or SAE requirement. Don't remember which. This was a requirement so someone traveling from, say, New York to California could top off their engine with any oil along the way with no problems. Is this good or bad? I don't know but I avoid.
I prefer to avoid mixing oils when possible. You end up with an oil that may or may not still meet specs. If you mix up a frankenbrew that's your choice, but I'd keep the oci on the short side.
It's not ideal to mix brands or additives. Additives are often a complete joke and in the realm of snake oil.
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