sometimes the book is best...

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Staff member
Dec 14, 2002
New Jersey

For a while now I have been thinking about what oil to use in my 91 BMW. Sonce the concensus is usually that a little thinner (to a point) is better, for more flow at startup, etc., I figured I would go M1 0w-40 or some such slightly lighter than reccomended oil. I had 5 qts of chevron havoline 20w-50 in my closet from the target sale a while back, and since it is the summer, I figured Id go with it anyway, even though thats about as thick as yu can get... nothing to loose really.
Well let me tell you, the car runs smoother, ticks less from the valves or tappets when hot, and gets the same MPG more or less as when I had diesel rated 15w-40 in it. Plus, it actually feel slike the power is there a bit more than previously.
So sometimes the book's oil that is givenb as the main viscosity for your temp range is indeed the best, I guess.

Now I have to think about the winter...
My next experiment will be M1 15w-50, as I wouldnt be worried about it in the winter in this engine, since my engine is healthy, starting wise, it does so well on 20w-50, and the M1 flows well in the cold, even in a 15 wt. But if for whatever reason, it doesnt seem to do as well, what else would have ok winter performance in a 15w-50 or 20w-50 tat I could buy reasonably and relatively available? Amsoil's 20w-50 oils didnt impress me with theirt cold viscosities and cold pouring points. I was thinking maybe castrol syntec blend in 20w-50 would be OK, but of course there is no info on that.
Any advise? I know its early, but I like to start shopping for new oil



[ July 15, 2003, 09:28 AM: Message edited by: JHZR2 ]
Too me the 15-50 is just too thick. I assume in DE the temperature rarely gets to zero-but that's still pretty cold for the 15W. I would consider mixing say 50/50 M1 10W-30 and 15W-50.

I would stay away from the Castrol Syntec blend bc a group III does not offer benefits in cold like a PAO. And to boot its a 20W
One thing that has always confused me about Mobil 1 15w50 is that they claim it can flow down to -49 degrees, but yet if it flows that well in the cold, how come it's not a 10w50 or a 5w50 for that matter? Or is this one of those oils that they choose to rate at the higher 15w rating, and could actually qualify for 10w or 5w status?

Or put another way, is it possible that 15w50 Mobil 1 can flow better in the extreme cold temps that are lower than the cold cranking tests for which 0w and 5w oils must pass but just doesn't flow as well at that temperature the test is taken at? In other words, if the temperature outside is at -30C (where a 5w's cold cranking ability is measured) is it possible that a 5w30 dino oil would flow better than the 15w50 Mobil 1, but then as the temperature gets even colder, the 15w50 Mobil 1 then goes the other way and outperforms the 5w30 dino on the cold cranking? Am I making sense here?

Amsoil's 20w-50 oils didnt impress me with theirt cold viscosities and cold pouring points. I was thinking maybe castrol syntec blend in 20w-50 would be OK, but of course there is no info on that.

-36° seems like a pretty good cold pour point for a 20W-50.....and methinks Syntec is not better...
Pour point of temp it can flow at does not mean much. Most straight 30 and 40 weights will flow at -30f (Chevron, Valvoline ect). But this flow will be a huge thick glob at the low temp. You need to look at cold cranking propeties, not pour point.
Well, if you didn't want to use M1 15W-50 "straight" in the winter, you could do what Al suggests & mix it with another M1. But I wouldn't use 10W-30. (There's not enough difference between 10W & 15W for me to feel it's any better off, & the huge gap between 30wt & 50wt would really thin out the hot vis.) My choice would be 50% (more or less) 0W-40. That way, you keep the hot end closer to the 50wt you know you want, but the xW- end gets a bigger drop.

It is kind of funny that you brought up 15w-50 and it flowing at low temperatures, because I have had the exact same question (if it flows so well why isn't it 5w or 10w?). I did an experement a couple of days ago to get an idea (mind you this is a pretty simple experement). I took a quart of M1 15w-50 and M1 0w-40 and put both of them in the freezer (my wife asked me why there was engine oil in the freezer!!!
) I left them in there for 24 hours to make sure they had time for the temperature to stabilize (btw the freezer is about 0-5F). I then took the bottles out, shook them, turned them, and opened them to see how the oil flowed.

What did I find. The M1 15w-50 had thickened significantly. At that tempurature it was approximately the consistancy of syrup from the refrigerator (which is still thinner than 20w-50 mineral is when it is 30F). Would the 15w-50 pump at 0F? Yes. Would I want to wait for it to get to the top of the motor, I don't think so.

By comparison the 0w-40 had thickened some, but was significantly thinner at 0F. The 0w was more like the 15w-50 is at 50f. Now the real question is how does the M1 10w-30 act at 0F (I have a bottle in the freezer chilling). I also need to get a quart of mineral 5w-30 or 10w-30 to see how thick they are at 0F.

I was just looking at Mobil 1's spec sheet, and you can see that their 15w50 would not qualify as a 10w by any stretch of the imagination, not with a spec of 14,050cP at -25C (it needs to be below 6000 at -25C to be a 10w)

I did notice something interesting though. It's kind of puzzling. In comparing their 0w40 to their 0w20, you can see that their 0w40 flows better at -35C, as it's spec is 4301cP, while 0w20 is 5550 cP. But yet they also list the CP at -40C and at this slightly lower temp now the 0w20 blows away the 0w40, with a spec of 12,000cP vs 21,700cP for the 0w40. How can this be? How could things shift around so much in just a 5C temperature difference? Or are these specs just wrong?
JonS, Patman, etc - of course pour point doesn't "mean much" (duh). The problem is that all the spec sheets (as noticed by Patman) seem to use a different temp for the real cold tests - and some don't even list specs
- I mean I know this is a bit different than what Patman is asking........something IS goofy.

But isn't the cold crank simulator, ASTM D 2602, supposed to be at -10°C or can a testing lab select whatever cold temp they want???
Jon hit the nail on the head. Look at the CCS numbers (which are SAE/API determined anyways) for cold performance...and not pour points. A pour point is simply the ability of the oil to move a couple cm down an incline. Big deal.

What this means though for M-1 15-50 is that it will do this slight movement down to temps as cold as a 5 or 10w. But, trust me at -20C, this stuff is thick as molasses....and is thicker than a 5 or 10w because it's...a 15w. It's just because it's a PAO that it will continue to be like molasses (useless state) down to the same point as conventional 5 or 10w. That's why the claim is no big deal...for us pro's.

As far as which oil for your `91 BMW....yes, the manual certifies a 15w down to -20C (and up to 40C+) and then goes to say that it's acceptable if the temps go above or below these limits for short periods. However, I switched to Syntec 5-50 because of better cold performance (the engine would knock heavily on starts)....yes, it is better because it's a 5w...even though the pour point is probably the same as the M1 15-50. Like I said, the PP is a just a number.

Originally posted by Pablo:
Patman wrote:


it needs to be below 6000 at -25C to be a 10w

Patman => Just curious - What are you using as your chart to compare vis. @ X° to SAE W number?

I'm sorry, but I'm not quite sure what you're asking me here.
Patman - IOW, an oil needs to be a certain viscosity at a certain cold temp. to qualify to be a 0W, 5W, 10W or whatever - I was just curious what you use as your chart or table for this. Is it here or is there a link?

Originally posted by Pablo:
Patman - IOW, an oil needs to be a certain viscosity at a certain cold temp. to qualify to be a 0W, 5W, 10W or whatever - I was just curious what you use as your chart or table for this. Is it here or is there a link?

OK, I see what you're asking now. I know there are links out there which show this, but I don't have them bookmarked unfortunately. I copied down the specs that someone else on here posted a few weeks ago, they are as follows:

10w has to pass with less than 6000cP at -25 C.

5w has to pass with less than 6000cP at -30 C.


I'm also going to assume that a 15w must be less than 6000 cP at -20c, and a 20w must be less than 6000 cP at -15c

Hopefully whoever posted this info will reference their link for us.
In the cold crank simulator, current specs are as follows:


Oil Grade Maximum Viscosity (cp)

0W 6200@-35C

5W 6600@-30C

10W 7000@-25C

15W 7000@-20C

20W 9500@-15C

25W 13000@-10C

There is also the cold pump test, but you won't see many oils post this data. I'm guessing the information on the Mobil 1 0w40 and 0w20 posted above at -40 C is the pump test, not the CCS test. The pump test is conducted at 5 degrees colder than the CCS test is.

A general rule of thumb (per the Lubrizol data where this info came from) is the Group I,II oils roughly increase viscosity by a factor of 2 for every 5 degrees colder, while Group III, IV increase by a factor of about 1.7.
So what are the implications of it being 2200 at -10? I mean, would it still be really slow flowing in my crankcase at say 10F, or would it be usable at that point?
Id love to stick with a 20w-50, but worry about oil flow in the cold...

I would say a 20W that has a viscosity of 2200 cp @ -10°C (14°F) is relatively low viscosity for a 20W. (Series 2000 20W-50) It would pump at 10°F (-12°C). Don't try this with petroleum motor oil!! That's why I was wondering about your comments.

That said, by all recommendations (including mine) 20W-50, even synthetic, is not really a winter oil of choice for most of the USA. I did use it in the Volvo turbo for two winters, maybe one time it was 15°F, and I had no problems. If it were my car, I would do it!
How cold are your winters? Amsoil 15w-40 is recommended for temps down to 5F.

[ July 22, 2003, 08:13 AM: Message edited by: BOBISTHEOILGUY ]
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