Thank you all for your replies to my first post. Changed my 15W 40 Rotella oil today for the Mobile synthetic 0W 40. Noticed immediately my idle oil pressure hovers at 2 bars instead of the normal 3-4, but rises to the normal 4-5 bars once the car is rolling. Will this lower oil pressure at idle cause premature wear? I'm nervous because my owner's manual calls for 20W 50 in summer but the new Porsche service bulletin recommends 0W 40.
Follow-up: 0W 40 or 20W 50 for a 1986 Porsche 944
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I guess the "approved oil only" camp descended on your original post. The oil sold and "approved" now is nothing like the oil from 25 years ago when your car was made.
For your climate, 15w-40 HD is perfect. I can't even add anything to that except maybe 10w-40 Hi-Miles oil would be a good too. If you drive lightly and had minimal consumption, maybe a 10w-30 would work too...try it in winter. Forget "synth" oil.
For your climate, 15w-40 HD is perfect. I can't even add anything to that except maybe 10w-40 Hi-Miles oil would be a good too. If you drive lightly and had minimal consumption, maybe a 10w-30 would work too...try it in winter. Forget "synth" oil.
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The difference is because M1 0w40 is a light 40-weight, whilst Rotella (much like Delvac 1 5w40, which would also be a good choice) is a heavy 40-weight. It is not going to cause issues.
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I`d stick with 20W50.
Originally Posted By: armydray13
Thank you all for your replies to my first post. Changed my 15W 40 Rotella oil today for the Mobile synthetic 0W 40. Noticed immediately my idle oil pressure hovers at 2 bars instead of the normal 3-4, but rises to the normal 4-5 bars once the car is rolling. Will this lower oil pressure at idle cause premature wear? I'm nervous because my owner's manual calls for 20W 50 in summer but the new Porsche service bulletin recommends 0W 40.
You're seeing the advantage of a modern high VI oil.
Besides 2 bar (29 psi) is plenty of oil pressure at idle.
Overall you're engine is receiving better lubrication.
Put your mind at rest and trust Porsche may know a little with their back spec'd recommendation.
Thank you all for your replies to my first post. Changed my 15W 40 Rotella oil today for the Mobile synthetic 0W 40. Noticed immediately my idle oil pressure hovers at 2 bars instead of the normal 3-4, but rises to the normal 4-5 bars once the car is rolling. Will this lower oil pressure at idle cause premature wear? I'm nervous because my owner's manual calls for 20W 50 in summer but the new Porsche service bulletin recommends 0W 40.
You're seeing the advantage of a modern high VI oil.
Besides 2 bar (29 psi) is plenty of oil pressure at idle.
Overall you're engine is receiving better lubrication.
Put your mind at rest and trust Porsche may know a little with their back spec'd recommendation.
I had a 1992 968 for 5 years or so, and researched the 944 and 951 platforms fairly extensively when I was shopping around as well. There are more similarities than differences.
Back when I owned the 968, I thought M1 was the best there is, and I was repeatedly told by mechanics that I "needed" 15W50. This was heavy stuff (API SJ days, I think? Red cap.) From my knowledge at the time, it was considered "normal" for the oil pressure warning light to flicker and pressure read 0.5bar or even lower at idle if you were running on the "thin" side and it was hot. I assume this would be 30s and thin 40s. This was in the owner's manual, and talked about in forums at the time. With my 15W50 I would idle at 2bar once fully warmed up (5bar when cold). Pressure would rise rapidly from 2bar as well to 4-5bar at most operating RPM ranges.
Your 2bar at idle is no problem at all. Porsche says down to 0.5bar is fine (but I certainly wouldn't be happy about it). I don't have it on hand, but Porsche specs how quickly it should rise (x bar per 1000 rpm) and that it should reach a minimum of y bar by z RPM. Those are the parameters you must be mindful of. Main bearing load while idling is virtually nil.
Now, before I sold the car I did one change with M1 0W40 since it was the new recommended weight for all Porsche I thought I'd give it a try. Idle was still around 1.5bar.
Now, I always thought the 15W50 was a bit thick. During warm up the engine was obviously fighting the oil and in the cool weather of spring and fall it was REALLY thick. So thick the gauge would slowly fall from 5bar to 0 over 5 seconds after shutting the engine off when still cold. Crazy.
The M1 0W40 really changed the character of the car. Start up and warm up was much more civilized and some pep was released at all temperatures.
If I knew then what I know now, I probably would run 15W40 HDEO and see what the startup/cold character was like. If high heat or track time was expected, probably 5W40 HDEO. If I bought a 968/944/951 again, I would not go the 15W50 route, and I would not go the M1 0W40 route. M1 0W40 shears pretty easy, and my 968 driving habits sheared even the M1 15W50, which does not shear easily.
Back when I owned the 968, I thought M1 was the best there is, and I was repeatedly told by mechanics that I "needed" 15W50. This was heavy stuff (API SJ days, I think? Red cap.) From my knowledge at the time, it was considered "normal" for the oil pressure warning light to flicker and pressure read 0.5bar or even lower at idle if you were running on the "thin" side and it was hot. I assume this would be 30s and thin 40s. This was in the owner's manual, and talked about in forums at the time. With my 15W50 I would idle at 2bar once fully warmed up (5bar when cold). Pressure would rise rapidly from 2bar as well to 4-5bar at most operating RPM ranges.
Your 2bar at idle is no problem at all. Porsche says down to 0.5bar is fine (but I certainly wouldn't be happy about it). I don't have it on hand, but Porsche specs how quickly it should rise (x bar per 1000 rpm) and that it should reach a minimum of y bar by z RPM. Those are the parameters you must be mindful of. Main bearing load while idling is virtually nil.
Now, before I sold the car I did one change with M1 0W40 since it was the new recommended weight for all Porsche I thought I'd give it a try. Idle was still around 1.5bar.
Now, I always thought the 15W50 was a bit thick. During warm up the engine was obviously fighting the oil and in the cool weather of spring and fall it was REALLY thick. So thick the gauge would slowly fall from 5bar to 0 over 5 seconds after shutting the engine off when still cold. Crazy.
The M1 0W40 really changed the character of the car. Start up and warm up was much more civilized and some pep was released at all temperatures.
If I knew then what I know now, I probably would run 15W40 HDEO and see what the startup/cold character was like. If high heat or track time was expected, probably 5W40 HDEO. If I bought a 968/944/951 again, I would not go the 15W50 route, and I would not go the M1 0W40 route. M1 0W40 shears pretty easy, and my 968 driving habits sheared even the M1 15W50, which does not shear easily.
You said " The M1 0W-40 really changed the character of the car. Start up and warm up was much more civilized and some pep was released at all temperatures."
That's one of the reasons (benefits) I run the lightest oil I feel I can safely use. A few years ago I saw a dyno comparison of various oils and oil grades which included M1 0W-40 and M1 15W-50. The hp gain with the 0W-40 over the 15W-50 I remember ranging from 8% to a minimum of 2% depending upon oil temp and rpm. That's a lot of "free" hp for just using the recommended oil grade.
As far as the tendancy of M1 0W-40 to shear. It tends to be very linear with mileage and Porsche does allow up to 15% of viscosity loss due to shear before reaching the condemnation point.
That's one of the reasons (benefits) I run the lightest oil I feel I can safely use. A few years ago I saw a dyno comparison of various oils and oil grades which included M1 0W-40 and M1 15W-50. The hp gain with the 0W-40 over the 15W-50 I remember ranging from 8% to a minimum of 2% depending upon oil temp and rpm. That's a lot of "free" hp for just using the recommended oil grade.
As far as the tendancy of M1 0W-40 to shear. It tends to be very linear with mileage and Porsche does allow up to 15% of viscosity loss due to shear before reaching the condemnation point.
Guys, I really appreciate the input. I think I'll send in an oil sample around 3,000 miles and see what it tells me.
Originally Posted By: CATERHAM
As far as the tendancy of M1 0W-40 to shear. It tends to be very linear with mileage and Porsche does allow up to 15% of viscosity loss due to shear before reaching the condemnation point.
Well, in only 6,000km my street-driven BMW 528 sheared M1 0W40 down into the 11s with no fuel or water dilution measureable. That's not cool, and one of the multitude of reasons I switched to GC in the BMW.
If I was driving even like I drove the 968 on the street it would have been worse. On the track? Unacceptable.
I've read here that M1 0W40 starts thickening again after it loads up with "stuff" on an extended interval. I don't think it would load up near fast enough to correct for this shearing. If I had left it in my 968 for two years without a change I still wouldn't be getting to "extended interval" either and I would not treat a fair-weather fun-car to anything longer than one year OCIs.
As far as the tendancy of M1 0W-40 to shear. It tends to be very linear with mileage and Porsche does allow up to 15% of viscosity loss due to shear before reaching the condemnation point.
Well, in only 6,000km my street-driven BMW 528 sheared M1 0W40 down into the 11s with no fuel or water dilution measureable. That's not cool, and one of the multitude of reasons I switched to GC in the BMW.
If I was driving even like I drove the 968 on the street it would have been worse. On the track? Unacceptable.
I've read here that M1 0W40 starts thickening again after it loads up with "stuff" on an extended interval. I don't think it would load up near fast enough to correct for this shearing. If I had left it in my 968 for two years without a change I still wouldn't be getting to "extended interval" either and I would not treat a fair-weather fun-car to anything longer than one year OCIs.
I hear what you're saying but down into the 11's cSt is not bad and still falls within the less than 15% shear that Porsche mandates.
How I interpret it is that modern Porsche's and most Bimmer's not need more than a heavy 30wt even with high oil temp's too meet their viscosity requirements.
How I interpret it is that modern Porsche's and most Bimmer's not need more than a heavy 30wt even with high oil temp's too meet their viscosity requirements.
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