Mixing 0W-40 & 15W-50 oil?
05-05-2003, 12:24 PM
#16
Another option is to do the reverse of fbfisher’s first post. He asked about adding one or two quarts of 15W-50 to a tank full of 0W-40. You could add a couple of quarts of 0W-40 to a tank full of 15W-50. This would give you a lighter oil at startup, which would help the lifters, but still retain the heavier oil for high temp use.
For example, let’s say there are 12 quarts total in a 993. If 3 were 0W-40 and 9 were 15W-50, you’d end up with oil pretty close to 11W-47. Not too bad.
On another note, I have a question for Chip. Up above, he says, “Lower viscosity oil is actually better for an engine - i.e. reduced frictional losses and reduced wear.” I can certainly see that lighter oil reduces frictional losses, but does it really reduce wear? (Let’s pretend that the oil has not reached the point of breaking down) Doesn’t make sense to me, but I’ve been wrong before. Chip also says “Higher viscosity oils will resist film breakdown under high temperature/load conditions better than low viscosity oils, but they may actually reduce engine output, and under non-severe conditions cause more wear to the engine.” I don’t understand how higher viscosity oils can cause more wear to the engine (at least once you’ve reached operating temperature).
Manufacturers are recommending lighter and lighter oils these days (like 5W-30). I’m thinking they are doing this for overall fleet mileage, not for engine longevity.
Tom
’95 993
For example, let’s say there are 12 quarts total in a 993. If 3 were 0W-40 and 9 were 15W-50, you’d end up with oil pretty close to 11W-47. Not too bad.
On another note, I have a question for Chip. Up above, he says, “Lower viscosity oil is actually better for an engine - i.e. reduced frictional losses and reduced wear.” I can certainly see that lighter oil reduces frictional losses, but does it really reduce wear? (Let’s pretend that the oil has not reached the point of breaking down) Doesn’t make sense to me, but I’ve been wrong before. Chip also says “Higher viscosity oils will resist film breakdown under high temperature/load conditions better than low viscosity oils, but they may actually reduce engine output, and under non-severe conditions cause more wear to the engine.” I don’t understand how higher viscosity oils can cause more wear to the engine (at least once you’ve reached operating temperature).
Manufacturers are recommending lighter and lighter oils these days (like 5W-30). I’m thinking they are doing this for overall fleet mileage, not for engine longevity.
Tom
’95 993
05-05-2003, 01:14 PM
#17
Addicted Specialist
Rennlist Member
Rennlist Member
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Manufacturers are recommending lighter and lighter oils these days (like 5W-30). I’m thinking they are doing this for overall fleet mileage, not for engine longevity. </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I agree. Likewise, manufacturers are increasing their service intervals so the "estimated service costs" are lower...yet another "bragging" point to consumers/fleet buyers/leasers. If I owned a BMW with "lifetime" tranny oil, would I ever change it? 
Edward
Edward
05-05-2003, 02:04 PM
#18
It would seem that a lighter oil could reduce wear if only because it gets to some parts of the engine faster than the thicker oil thus protecting them.
I agree completely that extended intervals between fluid changes are attempts by the manufacturers to appeal to customers on a reduced operating cost basis. This was the point that was made at the seminar with regards to total environmental pollution also. Less changes mean less pollution to the environment. It would seem this type of "reduced operating cost" thinking is behind much of the 100,000 mile tune up and spark plug changes that many manufacturers advertise.
However, a point was made during the seminar that many modern engines require and work better with modern thinner oil. Bruce Anderson specifically said that the 15w50 should not be used in a 996 nor a 986 engine. He explained in detail some of the reasoning but I don't remember the specifics. He indicated that 15w50 could be used in the 993 without the adverse effects that it causes in the 996 and 986 engine.
I agree completely that extended intervals between fluid changes are attempts by the manufacturers to appeal to customers on a reduced operating cost basis. This was the point that was made at the seminar with regards to total environmental pollution also. Less changes mean less pollution to the environment. It would seem this type of "reduced operating cost" thinking is behind much of the 100,000 mile tune up and spark plug changes that many manufacturers advertise.
However, a point was made during the seminar that many modern engines require and work better with modern thinner oil. Bruce Anderson specifically said that the 15w50 should not be used in a 996 nor a 986 engine. He explained in detail some of the reasoning but I don't remember the specifics. He indicated that 15w50 could be used in the 993 without the adverse effects that it causes in the 996 and 986 engine.
05-05-2003, 04:42 PM
#19
Pro
Join Date: Oct 2002
Location: Tulsa, OK
Posts: 637
Likes: 0
Received 0 Likes
on
0 Posts
Not only does lighter oil get to engine parts faster to reduce wear at startup, which may be where most engine wear occurs, but there is also less wear occuring under normal running conditions - barring film breakdown of course.
I'm finding it difficult to put into words, but basically oil molecules moving past metal also cause wear - even without metal to metal contact, though not at a great rate. Higher viscosity oil transmits more shear force to each surface of the bearing than lower viscosity oil, causing more wear. Higher viscosity oil also absorbs more of the motion energy at the bearing surfaces which translates into more heat at those surfaces.
How do rates of all of these different modes of wear compare to each other? I don't know - that is getting deeper into the dark arts of tribology than I have ventured....
Chip
I'm finding it difficult to put into words, but basically oil molecules moving past metal also cause wear - even without metal to metal contact, though not at a great rate. Higher viscosity oil transmits more shear force to each surface of the bearing than lower viscosity oil, causing more wear. Higher viscosity oil also absorbs more of the motion energy at the bearing surfaces which translates into more heat at those surfaces.
How do rates of all of these different modes of wear compare to each other? I don't know - that is getting deeper into the dark arts of tribology than I have ventured....
Chip
05-05-2003, 05:11 PM
#20
By the way, I've found lots of useful oil info at this site (No affiliation):
<a href="http://theoildrop.server101.com/ubb/ultimatebb.php" target="_blank">http://theoildrop.server101.com/ubb/ultimatebb.php</a>
Tom
'95 993
<a href="http://theoildrop.server101.com/ubb/ultimatebb.php" target="_blank">http://theoildrop.server101.com/ubb/ultimatebb.php</a>
Tom
'95 993
05-05-2003, 05:20 PM
#21
Pro
Join Date: Dec 2002
Location: Long Island,New York(Now in Orlando, FL)
Posts: 530
Likes: 0
Received 0 Likes
on
0 Posts
bet,Porsche recommends 15w50 for higher temps in the 986S owners manual.All new 986/996 come with 0w 40,but it specifically recommends serval oil viscosity ranges depending on ambient temps.Also I know many 986/996 owners who run there car with 15w50 in hot temps without adverse effects.
05-05-2003, 06:01 PM
#22
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by 914und993:
<strong>I'm finding it difficult to put into words, but basically oil molecules moving past metal also cause wear - even without metal to metal contact, though not at a great rate. Higher viscosity oil transmits more shear force to each surface of the bearing than lower viscosity oil, causing more wear. Higher viscosity oil also absorbs more of the motion energy at the bearing surfaces which translates into more heat at those surfaces.
Chip</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sounds like you're saying thicker oil causes more friction.
<strong>I'm finding it difficult to put into words, but basically oil molecules moving past metal also cause wear - even without metal to metal contact, though not at a great rate. Higher viscosity oil transmits more shear force to each surface of the bearing than lower viscosity oil, causing more wear. Higher viscosity oil also absorbs more of the motion energy at the bearing surfaces which translates into more heat at those surfaces.
Chip</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sounds like you're saying thicker oil causes more friction.
05-05-2003, 06:56 PM
#23
autobahnNY,
I was just repeating and passing along the information conveyed at the seminar. I do know that Porsche issues bulletins with revised oil recommendations, which are discussed in the tech sections on the PCA website where the oil viscosity issue is addressed quite frequently.
I don't know the specifics with regard to the 996/986 as I only inquired about the 993 engine. Along these same lines I found this on the PCA site where the tech advisor revised is first answer as more information became available:
"We are thinking that Porsche favors the 40 top weight over the 50 for street use because it is friendlier to the hydraulic valve adjusters (993 and 986/996) and other areas of the VarioCam valve train (986/996). In the case of the former, we have seen some of these newer cars struggle to achieve compression on startup in certain circumstances because the hydraulic valve adjusters are not pressurizing correctly.
So the revised answer is 'yes, it offers valvetrain advantages provided you keep the oil temperatures within specs'. In other words I will still run 15W-50 in my GT3 Cup car with the hydraulic valve adjusters because it is still heavier duty service than a 0-40 would be best for. But on the newer street cars the 0-40 is probably better if your climate is not hellaciously hot and you don't overdrive the car.
Joel Reiser / Bruce Anderson- PCA Website 2/02"
The question then is what is "hellaciously hot"? There is another question that touches on the viscosity debate that includes the updated oil recommendations that was answered in 2003 that those interested may want to check out.
I was just repeating and passing along the information conveyed at the seminar. I do know that Porsche issues bulletins with revised oil recommendations, which are discussed in the tech sections on the PCA website where the oil viscosity issue is addressed quite frequently.
I don't know the specifics with regard to the 996/986 as I only inquired about the 993 engine. Along these same lines I found this on the PCA site where the tech advisor revised is first answer as more information became available:
"We are thinking that Porsche favors the 40 top weight over the 50 for street use because it is friendlier to the hydraulic valve adjusters (993 and 986/996) and other areas of the VarioCam valve train (986/996). In the case of the former, we have seen some of these newer cars struggle to achieve compression on startup in certain circumstances because the hydraulic valve adjusters are not pressurizing correctly.
So the revised answer is 'yes, it offers valvetrain advantages provided you keep the oil temperatures within specs'. In other words I will still run 15W-50 in my GT3 Cup car with the hydraulic valve adjusters because it is still heavier duty service than a 0-40 would be best for. But on the newer street cars the 0-40 is probably better if your climate is not hellaciously hot and you don't overdrive the car.
Joel Reiser / Bruce Anderson- PCA Website 2/02"
The question then is what is "hellaciously hot"? There is another question that touches on the viscosity debate that includes the updated oil recommendations that was answered in 2003 that those interested may want to check out.
05-05-2003, 08:25 PM
#24
Pro
Join Date: Dec 2002
Location: Long Island,New York(Now in Orlando, FL)
Posts: 530
Likes: 0
Received 0 Likes
on
0 Posts
Brain,thanks for the in-depth info.In NY it gets outrageously hot and humid in the summer months.Hmm..I'll have to decide in the coming month or so on which oil to use.
05-05-2003, 08:43 PM
#25
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Thread Starter
Thanks again to all who have joined in with such helpful information. So the answer is that there is no problem mixing. The bigger issue seems to be in picking the proper weight in the first place.
It sounds like other than in "extreme temps" or hard driving (over driving?)0-40 is the way to go. Still need a definition of extreme temps, i.e. 405 fwy, bumper-to-bumper traffic, air temp 100+F qualify as extreme?
Sounds like a possible survey topic: "what is your climate/season/region and what weight oil do you use?"
It sounds like other than in "extreme temps" or hard driving (over driving?)0-40 is the way to go. Still need a definition of extreme temps, i.e. 405 fwy, bumper-to-bumper traffic, air temp 100+F qualify as extreme?
Sounds like a possible survey topic: "what is your climate/season/region and what weight oil do you use?"
05-06-2003, 02:27 PM
#26
Rennlist Member
For New York in the summer, why not use Castrol Syntec 5W50? The 5 weight behavior at low temps [edit: "means that at summer startup-temperatures the 5W50"] is kind[er] to the lifters [than the 15W50], and you get the protective 50 weight behavior at higher temps. [In other words, the 15W50 at temp of 80F is thicker/more viscous than 5W50 at 80F, and both are far thicker at 80F than at 190-220F operating temperature.] Syntec 5W50 is also on Porsche's official list of approved oils.
(Or is it heresy to consider anything besides Mobil 1? )
(Or is it heresy to consider anything besides Mobil 1?
)
05-06-2003, 11:32 PM
#27
Pro
Join Date: Oct 2002
Location: Tulsa, OK
Posts: 637
Likes: 0
Received 0 Likes
on
0 Posts
The Syntec 5W-50 is a synthetic oil, but to get that kind of range it has to be full of viscosity improvers.
Problems with viscosity improvers:
1. They break down with use, ultimately reducing the high temperature viscosity.
2. They aren't lubricative, and their volume displaces base stock oil which is.
I don't know how fast #1 occurs, or how significant #2 is. If the oil is changed frequently, Syntec 5W-50 is probably an excellent choice for typical street duty. For regular high load/high temperature use, like at the track, I don't think Syntec 5W-50 would be the best choice because of #2.
The same considerations probably apply for Mobil 1 0W-40. To get that range, it almost certainly has more viscosity improver in it than Mobil 1 15W-50.
Chip
Problems with viscosity improvers:
1. They break down with use, ultimately reducing the high temperature viscosity.
2. They aren't lubricative, and their volume displaces base stock oil which is.
I don't know how fast #1 occurs, or how significant #2 is. If the oil is changed frequently, Syntec 5W-50 is probably an excellent choice for typical street duty. For regular high load/high temperature use, like at the track, I don't think Syntec 5W-50 would be the best choice because of #2.
The same considerations probably apply for Mobil 1 0W-40. To get that range, it almost certainly has more viscosity improver in it than Mobil 1 15W-50.
Chip
