Would you put this BACK into your engine?

[artificialist]

Originally Posted By: Matt_N
Originally Posted By: artificialist
I wouldn't.

The ZDDP breaks apart over mileage, causing it to be less effective over time.


If you viewed the UOA I linked for the 5w50, you saw that I'm still at 900/800 ppm (Zn/P) with a TBN of 11.1 -- that's for used oil coming out of the Cayman.

That's more robust than many virgin oils out there. I'd say there is plenty of life left in the oil additive package.

Problem is, the Zinc breaks away from the phosphorus over time, that is why simply seeing those two numbers isn't enough. A UOA doesn't tell you how much the two have split.

 

[Quattro Pete]

Originally Posted By: artificialist
I wouldn't.

The ZDDP breaks apart over mileage, causing it to be less effective over time.

But that oil only has 2K miles on it. I'd say that's nothing for a modern fully synthetic oil. Do you dump your synthetic oil after only 2K miles because ZDDP broke apart?

I realize that 2K includes some track time, but still...

 

[fdcg27]

I wouldn't.
Oil for the BMW is too cheap to risk recycling the Porsche's oil in it, IMHO.
Also, the BMW six is not exactly a cheap engine.
It ain't a Cobalt or a Kia.
Now, if you had an old beater winter car or an abused old beater pickup or van, then why not reuse the M1 5W-50 in that?

 

[Matt_N]

Unfortunately, my only other option is my wife's Jetta TDI (PD motor)...and used 5w-50 probably isn't the way to go there. Not to mention, I have 8 gal of RT6 in the garage for it.

Ok -- new question

Do we know with some certainty what happens to either visc @ 40C or viscosity index (VI) as an oil is used?

For instance, in general, we know that visc @ 100C decreases as an oil is used (assuming no contamination or long OCI, etc). Does the same hold true for visc @ 40C? Does VI stay the same as an oil is used, since it is a proportional measure of visc at 40C and 100C??

The biggest question I'm now trying to answer is whether the used 5w50 oil will be too thick for winter service (temps down to 0F). If I can convince myself with data that it won't be too thick to try it, then I'll do the experiment and report back.

Thanks
Mat

 

[HTSS_TR]

I think it's too thick for winter use, you can use it in BMW from now until Nov-Dec.

 

[NewYorkBuck]

Honestly, it strikes me as a bit strange that someone who owns such cars would even consider such a move.

Porsche and BMW engines are extremely expensive. Motor oil is extremely cheap.

Proceed accordingly.....

 

[Matt_N]

Originally Posted By: NewYorkBuck
Honestly, it strikes me as a bit strange that someone who owns such cars would even consider such a move.

Porsche and BMW engines are extremely expensive. Motor oil is extremely cheap.

Proceed accordingly.....


It would strike many BITOG'ers as strange that I have been removing synthetic 5w50 oil from a vehicle after 2,200 miles and then dumping it. The oil still has a strong additive package and a TBN of 11.1, but has now sheared to a 40 weight. I would say the oil is still in serviceable condition...just not for the vehicle it came out of.

Rather than dumping this perfectly good oil and starting fresh, I'm trying to find a new home for it in another car. Look at the UOA for the 5w50 -- it's still as strong as many ACEA A3/B3 Xw-40! I just don't want to leave it in the Cayman because I prefer a 50 weight at the track.

My only concern before putting it in the BMW is that it may be too thick at lower temps -- I'm asking questions to try and quantify what the visc vs. temp curve would look like for the used oil so I can make an educated decision as to whether I want to try it.

 

[BMWTurboDzl]

The oil does not have LL01 correct? It very well may cause problems with the VANOS and I would not rely on the viscosity of a cheap UOA as a basis for your decision.

 

[A_Harman]

If you want a shear-resistant 50-weight, don't use a 5w50. Redline 20w50 would be as shear-resistant as you can get in a 50-weight. Even Redline 10w40 would have better HTHS than M1 5w50 after both are run on the track for 3-4 hours.

 

[A_Harman]

Originally Posted By: Matt_N
Do we know with some certainty what happens to either visc @ 40C or viscosity index (VI) as an oil is used?

For instance, in general, we know that visc @ 100C decreases as an oil is used (assuming no contamination or long OCI, etc). Does the same hold true for visc @ 40C? Does VI stay the same as an oil is used, since it is a proportional measure of visc at 40C and 100C??

The biggest question I'm now trying to answer is whether the used 5w50 oil will be too thick for winter service (temps down to 0F). If I can convince myself with data that it won't be too thick to try it, then I'll do the experiment and report back.

Thanks
Mat


You're obsessing too much over vis at 40C. This has nothing to do with the cold-temperaure performance of an oil. Since you're using a 5w-oil, it will have Cranking and Pumping viscosity properties that would be acceptable for use down to 0F. You can't use the high temperature properties of KV40, KV100, and VI to extrapolate viscosities very much below 20C when using viscosity calculators. At low temperatures, conditions such as the formation of wax crystals and the effect of pour point depressants make it impossible to predict viscosity.

 

[Matt_N]

^^

Thank you for the helpful reply. What you said makes sense; I'm starting with a 5w-xx oil, so the used oil will have low-temp properties no worse than the original 5w-xx oil. This means I should be able to continue to use the oil anywhere I would normally use a 5w-40 oil.

 

[dparm]

Oil is cheap, motors are not. M1 0w40 is $5/qt now at NAPA. I'd just go buy fresh oil.

 

[TomYoung]

I would save this solution for the post-apocalypse era.

 

[NewYorkBuck]

If you drink a bunch of water quickly, you could then probably drink your own urine with a minimal health implications, but is this a good idea?

I think you're focusing on viscosity itself a bit too much. You ran this oil in another engine. God knows what else it picked up in that process. Moisture, acids, other contaminants. Who knows.

I'll say the same thing as I said before. BMW and Porsche engines are very expensive. Motor oil is very cheap. IMO trying to economize on the latter while putting the former at risk is false economy.

 

[Malo83]

If you drink a bunch of water quickly, you could then probably drink your own urine with a minimal health implications, but is this a good idea?

I think you're focusing on viscosity itself a bit too much. You ran this oil in another engine. God knows what else it picked up in that process. Moisture, acids, other contaminants. Who knows.

I'll say the same thing as I said before. BMW and Porsche engines are very expensive. Motor oil is very cheap. IMO trying to economize on the latter while putting the former at risk is false economy. [/quote

No truer Words!

 

[GMorg]

Your question is not a new one. If you search for "Mobil 2", Mobil2, or M2, you may find some additional discussion. Several people here have had the same thought as you and refer to re-used Mobil 1 (M1) as Mobil 2 (M2). I think that one poster had over 10 years experience doing exactly what you are proposing -- different cars though.

 

[mcrn]

Originally Posted By: A_Harman
If you want a shear-resistant 50-weight, don't use a 5w50. Redline 20w50 would be as shear-resistant as you can get in a 50-weight. Even Redline 10w40 would have better HTHS than M1 5w50 after both are run on the track for 3-4 hours.


This is what I was thinking. Why not use an oil in the Porsche that does not shear to begin with? Simple solution to me and then you have no worries...both cars would have good oil in them and not worrying about all this?

 

[pavelow]

Save the oil and use it in your lawnmower or send it to me and I'll use it in my mowers. Must be nice to even consider running used engine oil in a fricking BMW. lol

 

[neunElf]

You should seek counseling!

 

[virginoil]

Originally Posted By: neunElf
You should seek counseling!


Sounds like he has too much time on hand.

Treatment suggested is to:
1. go and buy 2 x 5L jugs of the recommended factory fill oil
2. then tell the Missus that you will do full household chores for 2 weeks,
3. ensuring she fully relaxes and surfs BITOG on your behalf, and
4. whilst attending to her every wish and need.