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Ali Haas (Aehaas)
Junior Member
Username: Aehaas
Post Number: 51
Registered: 5-2003
| | Posted on Friday, July 04, 2003 - 12:30 pm: | |
I copied a very important fact from another poster---
Nick Scianna (Nick)
Posted on Thursday, October 18, 2001 - 3:19 am:
On the other end of the thermal spectrum, synthetic oils are also
renowned for their high-temperature thermal stability. Superior
high-temp stability ensures and engine lubricant's capacity to protect
vital engine components during very-high-temperature operation, such as
hot summer driving, sustained high-speed driving, repetitious stop and
go metropolitan driving, driving in mountainous terrain,etc.Underhood temperatures also take a quantum leap with the use of Turbos,Superchargers or power options,such as air conditioning b& because of emissions
devices and emissions-related engine redesign. It is important to note
that, even though the dash gauge may register only a 200F or so
water/coolant temperature, the temperature of the sump and of all the
assorted bearing surfaces significantly exceed the water temperature,
and OFTEN SURPASS 500F on the piston ring and cylinder wall areas.
These high-temperature surfaces serve to rapidly decompose petroleum oil
and additives, as well as contribute to their shorter service life,
while the synthetic is largely unaffected. Beyond the protection
afforded an engine during these particular instances of high-operating
temperatures, high-temp thermal stability moreover permits an engine
oil to deliver overall extended service life (significantly longer drain
intervals) in all driving conditions, because it prevents the phenomenon
of sludge and carbon deposit formations on critical engine parts
(valves, valve guides, oil channels,cam followers, piston rings,etc.
al.) due to oil thickening, a problem commonly attributable to petroleum
oil breakdown at high temperature. As these deposits accumulate in the
oil circulatory system, oil flow drops, thus accelerating engine wear.
To the user of synthetics, the benefits are (1) reduced wear of critical
engine components; (2) significantly reduced sludge and varnish... a
cleaner engine; (3) reduced engine drag due to uniform viscosity; and
(4) increased fuel economy due to reduced component wear.
Mobil Oil reported the results of simulated hot weather
performance with its Mobil 1 synthetic as evaluated by a standardized,
grueling engine test known as the Olds III-D. In this test, an
Oldsmobile 350" V8 engine is run for 64 hours at a 100-hp load and 300F
crankcase oil temperature. This test is designed to measure an oils
ability to resist oxidation and evaporation (and consequent thickening)
at high temperature. (If it seems odd that oil would *thicken* at high
temperature, consider the analogy of heating a pan of cold syrup on a
stove.At first it would become quite thinner, but if left for, say,
several hours, the resultant evaporation would cause the syrup to become
progressively thicker.) In order to qualify for the American Petroleum
Institutes top "SF" rating, a motor oil must pass the III-D test. This
means that it can thicken to no more than 375% of original viscosity at
the end of 64 hours of continuous running. Mobil states: "To test the
extra stability provided by the Mobil synthetic oil, we decided to run
the III-D *for 128 hours*...double its normal length...and without oil
drain. The Mobil 1 synthetic easily passed the test under these brutal
conditions, thickening only an insignificant 20%. For comparison, a
high-performance premium conventional oil was tested under identical
conditions. That test had to stop at 96 hours; the oil had turned
solid. Another premium conventional oil forced the the test to stop at
112 hours, well before the end of the scheduled double length." Amoco
Conducted an identical double-sequence III-D test on its Ultimate 5W-30
synthetic; it also passed the test with flying colors, thickening only
18%.
I am back. I will reiterate that in my thinking 50 percent of the oils function is cooling and cool parts wear less, all other things being equal. This again goes to say that thinner oil that gives the appropriate pressure will flow more, cool more and because it is cooler it will also be a little thicker. If you want a slightly thicker oil, use a thinner one. The engine will not get as hot so the oil will not get as thin.
Common sense is great but does not always give the scientific answer.
aehaas
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Ali Haas (Aehaas)
New member
Username: Aehaas
Post Number: 50
Registered: 5-2003
| | Posted on Thursday, July 03, 2003 - 11:36 am: | |
My 575 M oil gauge is redlined at 290 F. Again, these are sump temperatures where the oil comes to after leaving various engine areas. Some areas are hotter than others and some are thought to be as high as 300 or 400 F in the exact spot where the oil is doing its work.
aehaas |
Dave328GTB (Hardtop)
Member
Username: Hardtop
Post Number: 621
Registered: 1-2002
| | Posted on Wednesday, July 02, 2003 - 10:29 pm: | |
Ali,
The owners manuals all state that if oil get s to 250-260 range, it's time to slow down. This is true also of race cars. At 300 viscosity is gone and your motor will suffer. For track use, one wants an oil that's good up to 250 or so. It appears from your data that no oil is worth a dam at 300.
Dave
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Ali Haas (Aehaas)
New member
Username: Aehaas
Post Number: 48
Registered: 5-2003
| | Posted on Wednesday, July 02, 2003 - 1:48 pm: | |
Dave,
Actually the oil temperatures we quote from the engine are from the sump. The real temperatures at the bearing surfaces are thought to be 300 to 400 F. Numerous people report sump temperatures from 250 to 300 F when at the track. This is normal.
Around town sump temperatures run around 190 F plus or minus 20 I would guess.
aehaas |
Dave328GTB (Hardtop)
Member
Username: Hardtop
Post Number: 618
Registered: 1-2002
| | Posted on Wednesday, July 02, 2003 - 1:24 pm: | |
The numbers at 212 are more meaningful since any motor run to 300 degree oil is probably toasted and the numbers at 302 show why.
Dave |
Ali Haas (Aehaas)
New member
Username: Aehaas
Post Number: 45
Registered: 5-2003
| | Posted on Wednesday, July 02, 2003 - 10:17 am: | |
I just found more data...
SAE J300, viscosities at 212 F...
20, range - 5.6 to 9.2
30, 9.3 - 12.4
40, 12.5 - 16.2
50, 16.3 - 21.8
60, 21.9 - 26.1
By a modified analysis the min. viscosity at 302 F...
20, 2.6
30, 2.9
40, 2.9 - 3.7
50, 3.7
60, 3.7
Note again that the difference between the 20W and 60 weight oils at 302 F is only about 1 (one). Whereas the difference in viscosity at 104 F is 120 units. The 20W has a vs of 40 and the 60W a vs of 160.
Conclusion - At lower temperatures where most wear and tear occurs the difference in viscosity from 20W to 60W is large, while at high temperatures the viscosity difference is minimal, almost negligible.
aehaas
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