Oil mixing "standard"?

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Sep 25, 2002
Loveland, Colorado
This one's been bugging me for a while now, so I've finally decided to ask it here. For whatever reasons, everyone seems to be OK with mixing Mobil 1's 10W-30 & 15W-50 oils together, but not other grades. Why is that? What is it about these two very different oils that the same people who say "don't mix" have no reservations about mixing these? I guess they're kinda close at the xW- end, but they're worlds apart on the hot end of the scale. And their vis spread is not even close to one another, right? 20 pts for the 10W-30 versus 35 pts for the 15W-50. Doesn't it make at least as much sense to mix oils with similar vis spreads? Like M1 0W-30 & 15W-50? Or M1 0W-40 & 15W-50? Or D1 5W-40 & 15W-50? Or M1 10W-30 & 0W-20? Also, reading thru Mobil's literature, it seems as though the features & benefits of 15W-50 more closely match those of the 0W-40 than those of the 10W-30. I'm not promoting "home brewing" our own blends. I'm just trying to understand why one pair is accepted while others are rejected.
Only recently did M1 0W-40 become widely available (at AutoZone, etc.). I think that a lot of the 10W-30 + 15W-50 mixing was an effort to get something near a 40-weight when 0W-40 was hard to get.
Most people on here will agree that mixing oils of the same brand, with the same additive packages, is ok. It's the mixing of totally different oils which people frown upon. Although if you're going to do 3k intervals, it should not hurt anything, it's only if you try to do extended drains with a mixture where you might run into problems. As long as you do UOAs, mixing can be safe.
mph, I agree that this seems like the only way to get something close to a Mobil 1 10W-40, but do you think that's what people are going for? I still see folks recommending mixing 10W-30/15W-50 rather than recommending a switch to the 0W-40. Patman, I agree with all your points, but I'm still not clear about why these two oils are the standard for recommended mixing. LS-1 owners are big fans of this combo, right? Are many owners dropping their M1 mixes in favor of M1's 0W-40? Or do they routinely mix other M1 grades? And are most LS-1 mixers running UOAs on their oil? (Obviously, the ones here on BITOG may be, but I know you talk to a lot of LS-1 owners on other boards.) Thanks guys, -Greg [ June 25, 2003, 04:41 PM: Message edited by: Eiron ]
I've mentioned 0w40 Mobil 1 to many LS1 owners, but most cannot seem to find this viscosity easily, which is why they like to mix. It has helped quite a few guys reduce their oil consumption and piston slap issues. I've tried convincing a few of them to do UOAs, but most aren't interested. Most of them just like to use Mobil 1, change it every 2-3k and not worry about it. But yet at the same time, oil topics pop up quite frequently on the LS1 message boards, which is why I find it odd that so few have done UOAs.
My friend is going to mix Delvac 1 with M1 10w-30. I think this is a great combo, however, D1 is hard to find. You can order it though. He will be sampling some regular 10w-30 soon and I am going to send it off for him so we can get more LS1 UOA's. Next year I'll have him send off the D1 combo.
Delvac 1 is *incredibly* hard to find around here! I can find M1 0W-40 easily, and even the red label German Syntec 0W-30 is starting to show up. Thank goodness I don't own a TDi... Jason
Really? I see Delvac1 in every Walmart I've been to so far.. It's in the "heavy duty" section though. I think the 10w30/15w50 combo is so common for the reason stated above. People wanted something "thicker" than 10w30 but not as thick as 15w50. The 0w40 is still not very popular or readily available. And it's more expensive too.
One more reason for the popularity of mixing 10W-30 Mobil 1 with 15W-50 M 1 is that if you had a 2 to 1 ratio of 10W-30 to 15W-50 this would also be thicker at any temperature than 0W-40 M 1. This might be a benifit in an older car or something with a lot of miles. If I had a vehicle with a big block V8 I would use the 10W-30/15W-50 blend before I would use 0W-40. Also in a warm climate there may be little advantage in having such good cold pumping as the 0W-40 has in many older vehicles. That same blend of 10W-30/15W-50 also might have lower volatility (NOACK) but that is just speculation on my part. I have noticed people saying on this board that Walmart sells 0W-40 but here in Las Vegas where we probably have more European luxury cars than anywhere else they don't sell it. I bought some Mobil 1 10W-30 in a five quart jug that was on sale for $18.88 and also a quart of M 1 15W-50. I will mix four quarts of 10W-30 with one quart of 15W-50 in my wifes BMW.
Yeah, the WalMarts here in Northern CO don't carry the 0W-40 either; only the AutoZones. But at least the quarts are all the same price, regardless of grade or retailer. And the only Delvac anyone around here carries is the 1300 Super 15W-40. I'm not convinced that a 2:1 mix of 10W-30 to 15W-50 will really net you a thicker oil all around than 0W-40. Since 0W-40's 80cSt at 104*F, 10W-30's 62cSt, & 15W-50's 125cSt, I think you'd need at least a 1:1 mix to see an improvement over 0W-40 in the warm-up range. And then it looks like it's still going to be thinner when hot. (14.3cSt, 10.0cSt, & 17.4cSt at 212*F) It seems like it's always a one-way improvement that folks have in mind when they mix these two. That is, it's always to thicken up the 10W-30, rather than lightening the 15W-50. And the xW- end isn't as important as the hot end, right? I mean, people don't care if they've got a 12W- or 13W-, so long as the hot end gets that much bigger boost up towards 40. So, does anyone know a mixer who routinely uses 15W-50 & something else?
My Jeep 4.0L engine takes 6 quarts of 10W-30 oil...per manual specs...I use 4 quarts of 10W-30 and 2 quarts of 15W-50 (Mobil both) only in the summer oil change routine...oil gauge reads higher at idle when hot and has quieted down my piston slap quite a bit...I like to mix ...I mix greases also though [Big Grin]
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