Would you put this BACK into your engine?

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Matt_N

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Akron, OH
In the never-ending search for the PERFECT solution to oil for my fleet, I have an idea I wanted to run by BITOG for opinions and feedback.

I own a 2007 Porsche Cayman S. That vehicle sees quite a bit of track time, and I'm very happy with the results I'm getting with M1 5w50 (UOA HERE)

I also own a 2002 BMW 525i wagon (M54 BMW motor). I've been using Mobil 0w40 in the winter and 10w40 HM in the warmer months. No complaints

Here is my thought -- looking back at the UOA on the Cayman's 5w50 oil, it appears to have sheared to a 40 weight oil but still had an enormous TBN remaining (11.1), and was otherwise clean (fuel, insoluables, flashpoint all OK). I wanted to remove it from the Cayman before it sheared any further.

The question is would this used oil I'm removing from the Cayman be suitable for service in the BMW motor?

I tried to simulate the TEMP vs. VISC curve on the Widman.biz calculator; I know the 5w50 visc @ 100C after it comes out of the Cayman (my UOA was 14.4 @ 100C), but I'm not sure if the 40C visc will go up or down after the oil is used in the Cayman. Unless it goes down drastically (VOA = 108 @ 40C), then my used 5w50 is going to be VERY thick at cold temps. This concerns me. I don't think I'd run used 5w50 in colder temps without knowing UOA visc @ 40C and being able to plot the temp vs. visc curve.

Please chime in with any comments or thoughts. I'd love to hear from anyone with experience or data, or who can give me a feel for what happens to visc @ 40C after oil is used.

It would be too easy for me to drain the 8qts of used 5w50 (now sheared to Xw40) from the Cayman, and dump 7qts of it into the BMW for continued service.

Thanks in advance,
Matt
 
Because it's sheared to 14.4cSt @ 100C. Because of the frequent track conditions the car sees, I'd like to keep the oil in there as close to a 50w as possible -- personal preference.

But, now that I've "conditioned" that oil down to a 40 weight...maybe it's just right for my BMW motor.
 
Originally Posted By: Steve S
If the oil is still good enough to use in another car why drain it from the Porsche?


SHEARING

If you can transfer it carefully enough, I'd run it. Although if I could afford a Porsche and a BMW...

Edit: Is the bmw really at the bottom of your fleet? Maybe pick a less favored car? 11 tbn is really kind of high to throw away. Have you experimented with other oils maybe not shearing as much?
 
I dont have a problem with it. Just make sure you know the oil is serviceable (Would hate to subject the bearings in both cars to antifreeze) and keep a record of the UOA/VOA so you know what your starting baseline is.
 
Probably the oil would thicken up with more use. Give the post some time and there will be the people who will recommend 20 wt. I looked a buying a Cayman in late 2009 and isn't the oil change interval 10,000 miles? I really like Porsches by the way. I came really close to writing the check but what stopped m is there are no dealers in the area to get parts from with ease.
 
Drain the oil from the Cayman into a clean container, use double coffee filter to catch any debris from the drained oil into another clean container before pour it into the BMW. The process of filtering is very slow, it may take more than 1 hour per quart.
 
I dont blaim you. If a car actually needs a 40 weight for street use I think it would need at least a 50 weight for opentracking.

Im certainly not going to have my Mustang 5.0L out on the track with oil temps of 285F or above on 5W20. Although I have absolutely no qualms about it for street use.
 
I think it would be a good idea to reuse the oil in the BMW, so long as UOA indicates that everything is in order other than the shearing.
 
Are you SERIOUS!!! a PERFECT solution
crackmeup2.gif
 
I was a bit humored by this idea initially, but the more I think about it, the more it makes sense, especially seeing that UOA from your Cayman. I'd say give it a try. The M54 engine isn't typically very demanding when it comes to oil.
 
How 'bout this...

Does anyone have a feel for what generally happens to visc @ 40C once oil is used?

My M1 5w50 starts at 108cst @ 40C before it is used. Any guesses to where it would be after 100C visc drops to 14.4cSt from 17.5cSt??

If I have a feel for what happens to 40C visc, I can plot the visc. vs. temp. values and compare my "used" oil viscosity to various new oils suited for the BMW.
 
Originally Posted By: Matt_N
If I have a feel for what happens to 40C visc, I can plot the visc. vs. temp. values and compare my "used" oil viscosity to various new oils suited for the BMW.

BMW doesn't really spec a particular viscosity for this engine. It just requires LL01 oil which means ACEA A3, which means HT/HS of at least 3.5 cP. You could be running a 10w-40 oil and still be meeting these specs.
 
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.
 
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