Mixing synthetic oil and regular oil?

[Rick L]

Is it O.K. to mix synthetic oil and regular oil? I recently brought my BMW into the dealership and they added 1.5 quarts of regular oil to the synthetic oil already in the car. Since the oil change was done recently and not due for a while, is it O.K. to have the mixed oil?

[Hector]

term you reduce the superior antiwear properties of synthetic oil, which therefore, increases engine wear. Synthetic oil is engineered to be stable over a wide temperature range which translates to stable viscosity. You get the same degree of protection when the oil is hot just as when it is cold. For dino oil (or regular oil,) modifiers are added in an attempt to prolong stability over a wide temp range so that when it is cold the oil doesn't get too thick, and when it's hot it doesn't get too thin. Such stability, however, is short-lived.

Dino oil hurts the engine during cold start because the oil is thick and there is hardly any lubrication available which causes engine wear. When the oil is hot it becomes very thin and you get nearly metal-to-metal contact which also causes engine wear.

With synthetic oil, you enjoy it's benefits because the oil is stable over a wide temp range for a long time. You get the same thickness, and therefore same level of protection whether the engine is hot or cold... the engine runs cooler and engine parts don't wear out as quickly.

Having said all this, mixing synthetic with regular oil reduces the effectiveness of the former oil to combat engine wear.

[Rick L]

Thanks for the information... Maybe I should have told them not to add additional engine oil. How many quarts do the 1995 525i take anyway? I did my own oil change with Mobil 1 0W-40 and added 6.5 quarts of oil. The dipstick looked O.K. three weeks ago. I have no leaks what so ever and don’t think I burn any oil either. The Fields BMW service department told me they added almost 2 quarts... WHERE DID MY OIL GO?!?!? Anyway, I’ll take the safe route and change the mixed oil with full synthetic to be sure that there are no conflicts between two different types of oil. I still have an extended warranty for this car that’s about to expire soon and like to keep the car for another two or three years (it only has 75k on the clock).

[Unregistered]

Is it O.K. to mix synthetic oil and regular oil? I recently brought my BMW into the dealership and they added 1.5 quarts of regular oil to the synthetic oil already in the car. Since the oil change was done recently and not due for a while, is it O.K. to have the mixed oil?


Doesn't hurt it at all, don't worry about it. Hector is incorrect about synthetics supposed "superior antiwear properties." Synthetic oils offer 1) Wider weight spans with less VI improvers, and 2) longer change intervals. FYI a 10w oil is a 10w oil at -20f whether it is a synthetic or a mineral oil. If you want superior lube on startup, go to a 5w or a 0w which will be thinner at the same cold temps.

If you want more info on synths, go to bobistheoilguy.com for more info than you will ever want and extended discussions.

[632 Regal]

Heres a quote from Bobs the guys site...

synthetic oils

Oils produced by synthesis (chemical reaction) rather than by extraction or refinement.
Many (but not all) synthetic oils offer immense advantages in terms of high temperature stability and low temperature fluidity, but are more costly than mineral oils.
Major advantage of all synthetic oils their chemical unformity.

[Hector]

you obviously didn't catch my drift. Read the post again, and again...


Hector is incorrect about synthetics supposed "superior antiwear properties." Synthetic oils offer 1) Wider weight spans with less VI improvers, and 2) longer change intervals. FYI a 10w oil is a 10w oil at -20f whether it is a synthetic or a mineral oil. If you want superior lube on startup, go to a 5w or a 0w which will be thinner at the same cold temps.

If you want more info on synths, go to bobistheoilguy.com for more info than you will ever want and extended discussions.

[Bill R.]

10w oil is a 10w oil at -20f regardless of whether its synthetic or not..Thats not true.. The lower number on oil viscosities is arrived a 0 degrees F and many 10w dinos are not 10w anymore at -20 whereas most if not all synthetic undergo very little viscosity change from 0 to -20










you obviously didn't catch my drift. Read the post again, and again...

[Unregistered]

10w oil is a 10w oil at -20f regardless of whether its synthetic or not..Thats not true.. The lower number on oil viscosities is arrived a 0 degrees F and many 10w dinos are not 10w anymore at -20 whereas most if not all synthetic undergo very little viscosity change from 0 to -20


Uh, sorry but wrong. The lower weight number is not tested at 0F. In fact it depends on weight. It breaks down as follows:

0W 3250 @ -30C
5W 3500 @ -25C
10W 3500 @ -20C
15W 3500 @ -15C
20W 4500 @ -10C
25W 6000 @ -5C

The thickeness measurement is viscosity in Centastokes. So when you look at an oil that is rated as 10w it doesn't matter if it is synthetic or Mineral, it has to be less than 3500 centastokes at -20C. If it was significantly thinner at that tempurature it would be thin enough to be called a 5w.

The advantage of synthetics at cold temps is that you can formulate 0w oil which requires so many VI improvers with a Mineral Group I or II oil (we will for purposes of this discussion consider Group III hydrocracked base stocks to be synthetic, even though that is debatable) that the oil would not be functional and break down in short order. Because synthetics also have a higher VI (viscosity index) than mineral oils you can have a wide weight span that mineral oil could not (same reason of to many VI improvers in the mineral). So Synthetics allow for you to purchase oils like 0w-40 or 5w-40 which cover all temps.

Finally, even synthetics undergo significant thickness changes from 0f to -20F. If you would like to e-mail me, I would be happy to provide the PDF charts from Mobil showing the thickness of their various oils accross all tempurature ranges. The oils whether synthetic or mineral thicken at the nearly the same rate with only minor differences in the slope of the thickness curve between the two types of oil (note the graph shows a straight line, but it is in fact a logrithmic scale).

Here is some more info on measuring the thickness of oil:

http://www.wearcheck.com/literature/techdoc/WZA007.htm


Cary@ifn.net

[Bill R.]

read that the viscosity ratings for oils were arrived at 100 C and at 0 C for
w oils... but everything i find states the same as what you're saying.









Uh, sorry but wrong. The lower weight number is not tested at 0F. In fact it depends on weight. It breaks down as follows:

0W 3250 @ -30C
5W 3500 @ -25C
10W 3500 @ -20C
15W 3500 @ -15C
20W 4500 @ -10C
25W 6000 @ -5C

The thickeness measurement is viscosity in Centastokes. So when you look at an oil that is rated as 10w it doesn't matter if it is synthetic or Mineral, it has to be less than 3500 centastokes at -20C. If it was significantly thinner at that tempurature it would be thin enough to be called a 5w.

The advantage of synthetics at cold temps is that you can formulate 0w oil which requires so many VI improvers with a Mineral Group I or II oil (we will for purposes of this discussion consider Group III hydrocracked base stocks to be synthetic, even though that is debatable) that the oil would not be functional and break down in short order. Because synthetics also have a higher VI (viscosity index) than mineral oils you can have a wide weight span that mineral oil could not (same reason of to many VI improvers in the mineral). So Synthetics allow for you to purchase oils like 0w-40 or 5w-40 which cover all temps.

Finally, even synthetics undergo significant thickness changes from 0f to -20F. If you would like to e-mail me, I would be happy to provide the PDF charts from Mobil showing the thickness of their various oils accross all tempurature ranges. The oils whether synthetic or mineral thicken at the nearly the same rate with only minor differences in the slope of the thickness curve between the two types of oil (note the graph shows a straight line, but it is in fact a logrithmic scale).

Here is some more info on measuring the thickness of oil:

http://www.wearcheck.com/literature/techdoc/WZA007.htm


Cary@ifn.net

[ryan roopnarine]

bill, whilst you're a captive audience........you live in arizona so i assume that your car is exposed to the warmer environs. i've heard sooooo many people say that i shouldn't be running m1 5w30 in my 40k-50k mile m50...right now temp is around 85, and by summer should be unbearably hot here....should i be using the 15w50 or 10w30 instead?

[Bill R.]

problem and my ambient is at least as high as yours...probably much higher in the middle of summer... And the 5w30 is on bmw's list on approved synthetics for all temps... that said I will be switching to 0w40 mobil one on my next change because i like the wider spread.. I just changed oil on a civic yesterday with 5w20...hard concept to get used to...









bill, whilst you're a captive audience........you live in arizona so i assume that your car is exposed to the warmer environs. i've heard sooooo many people say that i shouldn't be running m1 5w30 in my 40k-50k mile m50...right now temp is around 85, and by summer should be unbearably hot here....should i be using the 15w50 or 10w30 instead?

[Hector]

One question though, since the graphs have log scales, is it fair to say that n<subD> changes rapidly at low T but doesn't vary much at high T?


Uh, sorry but wrong. The lower weight number is not tested at 0F. In fact it depends on weight. It breaks down as follows:

0W 3250 @ -30C
5W 3500 @ -25C
10W 3500 @ -20C
15W 3500 @ -15C
20W 4500 @ -10C
25W 6000 @ -5C

The thickeness measurement is viscosity in Centastokes. So when you look at an oil that is rated as 10w it doesn't matter if it is synthetic or Mineral, it has to be less than 3500 centastokes at -20C. If it was significantly thinner at that tempurature it would be thin enough to be called a 5w.

The advantage of synthetics at cold temps is that you can formulate 0w oil which requires so many VI improvers with a Mineral Group I or II oil (we will for purposes of this discussion consider Group III hydrocracked base stocks to be synthetic, even though that is debatable) that the oil would not be functional and break down in short order. Because synthetics also have a higher VI (viscosity index) than mineral oils you can have a wide weight span that mineral oil could not (same reason of to many VI improvers in the mineral). So Synthetics allow for you to purchase oils like 0w-40 or 5w-40 which cover all temps.

Finally, even synthetics undergo significant thickness changes from 0f to -20F. If you would like to e-mail me, I would be happy to provide the PDF charts from Mobil showing the thickness of their various oils accross all tempurature ranges. The oils whether synthetic or mineral thicken at the nearly the same rate with only minor differences in the slope of the thickness curve between the two types of oil (note the graph shows a straight line, but it is in fact a logrithmic scale).

Here is some more info on measuring the thickness of oil:

http://www.wearcheck.com/literature/techdoc/WZA007.htm


Cary@ifn.net

[Rick L]

I brought my car back to the dealer because the BMW service tech over filled my car with two quarts too much. I CANNOT believe a BMW tech could make that kind of a mistake... Anyway, the BMW service manager said that the BMW recommends 5W-30 for synthetic oil for my car and did an oil change with 5W-30 synthetic. But I would use 0W-40 synthetic (Mobil 1) next time since I had 0W-40 synthetic oil in my car before the dealer over filled my car with engine oil and it ran great with 0W-40!



bill, whilst you're a captive audience........you live in arizona so i assume that your car is exposed to the warmer environs. i've heard sooooo many people say that i shouldn't be running m1 5w30 in my 40k-50k mile m50...right now temp is around 85, and by summer should be unbearably hot here....should i be using the 15w50 or 10w30 instead?

[ryan roopnarine]

the fields bmw you went to wouldn't happen to be fields of winter park, florida would it?


I brought my car back to the dealer because the BMW service tech over filled my car with two quarts too much. I CANNOT believe a BMW tech could make that kind of a mistake... Anyway, the BMW service manager said that the BMW recommends 5W-30 for synthetic oil for my car and did an oil change with 5W-30 synthetic. But I would use 0W-40 synthetic (Mobil 1) next time since I had 0W-40 synthetic oil in my car before the dealer over filled my car with engine oil and it ran great with 0W-40!

[Unregistered]

I believe the oil does thicken relatively faster at cold temperatures than high. To give an idea, a 30 weight oil is between 9.3 and 12.5 cst @ 100c and 40 weight between 12.6 and 16.? cst @ 100c. At 40C a 5w-40 oil is approximately 80-100 cst. Compare to the 3500cst cold starting thickness.

BTW, I know that BMW NA approves of Mobil 1 5w-30 but it is just to thin of a oil to use, and I would not recommend it. Mobil 1 30 weight synthetics are formulated on the thin end of 30 weight oils (9.8 cst @ 100c) and are nearly a 20 weight oil. I would only use oils that are A3 rated (generally heavy 30 weight and heavier, but more importantly having a HTHS of 3.5 or great, HTHS being a measurement of high tempurature (150c) high pressure protection. Mobil 1 0w-40 and 15w-50 both meet this spec. Note that BMW Synth 5w-30 is also a A3 oil and is a very heavy 30 weight (CST of 12.2-12.4 @ 100c). I don't recommend the BMW Synth oil because it is a Group III oil instead of a group IV oil like Mobil 1. For the same price, the Mobil is better.

For all around use, I like the Mobil 1 0w-40. It meets BMW Long Life 01 requirement (basically A3), Mercedes Benz 229.3 and 229.5 (very strict tests for oxidation resitance) and is factory fill for Porsche, Mercedes AMG and Austin Martin. If you are tracking the car, I would use Mobil 1 15w-50. Note that for every 30F increase in oil tempurature, it thins approximately one grade. So that oil that is a 30 weight at 210F, thins down to be as thin as 20 weight at 240F. It is not uncommon to see oil temps at the track or driving schools of 240-270f, compared to about 210f on the street.

Cary

[Rick L]

The Fields BMW I brought my car to is the one in Northfield, IL. I believe there is one in Winter Park, FL and Lakeland, FL as well.





the fields bmw you went to wouldn't happen to be fields of winter park, florida would it?

[Bill R.]

website, both of them are a acea a1,b1,a5,b5 and neither is listed as an a3 but the 0w30 castrol is an a3 but it doesnt meet the a1, a5 specs..






I believe the oil does thicken relatively faster at cold temperatures than high. To give an idea, a 30 weight oil is between 9.3 and 12.5 cst @ 100c and 40 weight between 12.6 and 16.? cst @ 100c. At 40C a 5w-40 oil is approximately 80-100 cst. Compare to the 3500cst cold starting thickness.

BTW, I know that BMW NA approves of Mobil 1 5w-30 but it is just to thin of a oil to use, and I would not recommend it. Mobil 1 30 weight synthetics are formulated on the thin end of 30 weight oils (9.8 cst @ 100c) and are nearly a 20 weight oil. I would only use oils that are A3 rated (generally heavy 30 weight and heavier, but more importantly having a HTHS of 3.5 or great, HTHS being a measurement of high tempurature (150c) high pressure protection. Mobil 1 0w-40 and 15w-50 both meet this spec. Note that BMW Synth 5w-30 is also a A3 oil and is a very heavy 30 weight (CST of 12.2-12.4 @ 100c). I don't recommend the BMW Synth oil because it is a Group III oil instead of a group IV oil like Mobil 1. For the same price, the Mobil is better.

For all around use, I like the Mobil 1 0w-40. It meets BMW Long Life 01 requirement (basically A3), Mercedes Benz 229.3 and 229.5 (very strict tests for oxidation resitance) and is factory fill for Porsche, Mercedes AMG and Austin Martin. If you are tracking the car, I would use Mobil 1 15w-50. Note that for every 30F increase in oil tempurature, it thins approximately one grade. So that oil that is a 30 weight at 210F, thins down to be as thin as 20 weight at 240F. It is not uncommon to see oil temps at the track or driving schools of 240-270f, compared to about 210f on the street.

Cary

[Unregistered]

website, both of them are a acea a1,b1,a5,b5 and neither is listed as an a3 but the 0w30 castrol is an a3 but it doesnt meet the a1, a5 specs..

The reason is that:

A1= HTHS of less than 3.4, no long life oil requirement.
A2= Not Used
A3= HTHS of greater than 3.5, hi performance oil suitible for extended changes.
A4= For Direct Gas engines, no standard yet.
A5= HTHS of less than 3.4, long life oil for engines designed for low HTHS oils (newer volkswagens/audis). If an oil meets A5, it automatically meets A1


So as you can see, an oil cannot be A3 & A5 or A1, as they are mutually exclusive due to HTHS. So you will find that Mobil 1,20 and 30 weights are ACEA A5 oils and 40 and 50 weights are A3 oils.

BTW, watch out with the 0w-30 Castrol as there are two formulas. There is the american made (Group III+) and the German Made (Group IV/V). The German Castrol is a great oil, identified by the red label and that it says on the back "made in germany."


Cary

[Travelfeet]

Since the interior of my engine is at least 200+ degrees Fahrenheit when at operating temperature, why should I care about using a heavier oil just because its 100 degrees ambient? If thinner oil pumps well at operating temp (it must since the internal engine temp is not different in any climate) why won't this thinner oil suffice for initial lubrication in Arizona etc... as well as below zero. It has always seemed to me any oil that works in extreme cold should be just fine in the heat. It's never going to be hotter ambient than inside your engine. I have also never heard that a lighter weight oil wears out any quicker. Why should I ever be concerned with changing the oil weight in relation to the climate where I live? I have always thought that within day to day driving applications (not racing) most of the difference in application of oil weights is marketing and hype, so what am I missing?

[Unregistered]

Your missing two things:

1) Until recently you could't get oils that had wide weight spans and covered all climates; i.e. 0w-40 and 5w-40 which have come about due to wide use of Synthetics.

2) Oil temp at operating speeds will absolutely change depending on outside tempurature. Depending on the car, you may find a 60F swing driving at 65mph on the freeway depending on if it is 0f out or 100f.

Have to run, baby is fussing.