Mixing diferent oil weights in between changes?

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122
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Franklin, TN
I changed my oil about 400 miles ago on my 95 camaro using 10w30 mobil 1 and an STP filter. The motor has 130k miles, and has loosened up enough where I want to run a little bit thicker oil, especially since it's been in the high 90's here in tennessee for the past little bit. I have a pretty steady oil leak coming from the timing cover(which will be fixed after this oil change) and was wondering if it would be ok to add a quart of 15w50 mobil 1 to the mix when it gets low. John
 

Patman

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Guelph, Ontario
You can definitely do this and you might find it lessens the leak too. A lot of LS1 f-body owners put in 2qts of 15w50 and 4qts of 10w30 every oil change. They found this lessens their oil burning by quite a bit (I still think they should simply try switching to 10w30 Amsoil or Redline, or 10w40 Amsoil or Redline in severe oil burning cases) Just a warning to those in colder climates though, once the cool fall weather rolls around you won't want to still be doing the 15w50/10w30 mixture, since the addition of the thicker 15w50 will greatly reduce the cold cranking ability of your oil. 15w50s viscosity at 40c is double that of the 10w30!
 
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quote:
You can definitely do this and you might find it lessens the leak too. A lot of LS1 f-body owners put in 2qts of 15w50 and 4qts of 10w30 every oil change. They found this lessens their oil burning by quite a bit (I still think they should simply try switching to 10w30 Amsoil or Redline, or 10w40 Amsoil or Redline in severe oil burning cases)
I have a friend who recently bought a new Vette. I told him he could mix in a qt of 15w-50 but he is stubborn and won't do it. He is thinking of trying Amsoil 0w-30 which IMO would be an excellent choice for this car.
 
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Fastzntn When you mix different viscosities, the result is not the average of what you mix. The only way to know is to do an analysis if the resulting viscosity. Do the oils really mix?...I mean on the molecular level, and I don't know the correct term for the 30 wt. and 50 wt. molecules happy side-by-side [Smile] but still separate. Won't the remaining 10W-30 continue to leak past that bad gasket and tend to leave the bigger 15W-50 molecules behind? Ken [ August 17, 2003, 01:58 PM: Message edited by: Ken2 ]
 

Fastzntn

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I'm not too worried about the leak since it will be fixed soon. You brought up an interesting question about mixing- will the oils actually mix, or could they separate leaving a sort of layering effect? John
 

Patman

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Guelph, Ontario
quote:
Originally posted by buster:
quote:
You can definitely do this and you might find it lessens the leak too. A lot of LS1 f-body owners put in 2qts of 15w50 and 4qts of 10w30 every oil change. They found this lessens their oil burning by quite a bit (I still think they should simply try switching to 10w30 Amsoil or Redline, or 10w40 Amsoil or Redline in severe oil burning cases)
I have a friend who recently bought a new Vette. I told him he could mix in a qt of 15w-50 but he is stubborn and won't do it. He is thinking of trying Amsoil 0w-30 which IMO would be an excellent choice for this car.

He should just stick to the 5w30 or 10w30 Amsoil, since most likely he won't be doing 35k oil changes, and he'll save money with the 5w30 or 10w30 ASL/ATM stuff. Plus both of those are closer to 11.7-11.9cst, while the 0w30 is 11.3 I believe.
 
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Location
Washington St.
quote:
Originally posted by Fastzntn: I'm not too worried about the leak since it will be fixed soon. You brought up an interesting question about mixing- will the oils actually mix, or could they separate leaving a sort of layering effect? John
No, they won't separate at all, but you still have 10W-30 and 15W-50 oil, not 12.5W-40. Ken
 

Al

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Elizabethtown, Pa
Well I'm not disagreeing here, but the net effect at mixing on the molecular level will be less leakage because the seal will see a percentage of 15W-50 molecules that won't leak by as well. As far as the viscosity- The bigger molecules will just drag down the kinematic/absolute viscosity. I think mixing the two is a great idea. For all intense and purpose mixing on the molecular level produces a homogeneous liquid with a higher viscosity. (IMHO) Just for some real world numbers: with a 30% (approx) mix of 15W-50 my viscosity jumped from the usual 10 sSt to 11.25 cSt (12.5 is a 40 wt). Bottom line-a 25% mixture will put you in the sweet part of a 30 wt for Mobil 1.
 
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Location
Oregon
I never worry about mixing a little oil (wt. or brands) for between oil changes. That is how I get rid of odds and ends. Been doing it for decades with no problems. But I do change my oil every 3000 - 3500 miles so that might be why I have never hurt anything.
 

Patman

Staff member
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Guelph, Ontario
One thing that has me curious is that if you mix two oils, how does it affect the HTHS? I wonder if it becomes an average of the two, or if it leans more towards the lower side? For instance, if you mix in Mobil 1 5w30 (with it's 3.08 HTHS) and Mobil 1 15w50 (with it's 5.11 HTHS), in an exact 50/50 ratio, will the resulting HTHS number then become 4.1? We know the viscosities might not behave exactly like this, due to different levels of VII in each oil, however the resulting viscosity should be pretty close to 91cst at 40c, and 13.7 cst at 100c, give or take a few %. So in effect you'd have something close to a 10w40 to 15w40 oil probably. Someone please test this out! [Smile]
 
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