derporsche928

Viscosity is a measure of an oils resistance to flow, and a thicker oil will have better oil pressure, but will not flow as well, and the best we can hope is to split the difference with some good quality synthetic snake oil.......
Aargh....! .... Pressure - flow, pressure - flow, pressure - flow, pressure - flow, pressure - flow....

Someone should invent a universal fantastic oil and call it oily-oil, and be done with it.
(I'm also looking for some greasy-grease for my axles and wheel bearings.....)

Hope this helps,
Greg

heinrich

I haven't run dino oil in Godzilla for over 7 years. i ran Mobil One Synth 15W-50 for years and switched to Delvac synth last year (early). The oil pressures have not changed at all, either at idle or under FULL load. Same. I get about 2.75 - 3 BAR at idle and a full 5 at any sort of load and NEVER inbetween. Never.

Godzilla is (I've been carefully monitoring this) showing at sea level, 16mpg in town and daily driving in WINTER and since it's now summer I have been getting 18mpg+ city / 20mpg+ SPIRITED highway/mixed. And I mean spirited.

Godzilla seems to be making excellent power. Oil consumption is perhaps a quart every 10,000 miles the past year. That is definitely higher than when I was using Mobil One Synth, but these are miniscule values.

heinrich

OK I am no scientist, BUT

1) The Porsche 928 oil pump has a flow production rate of FAR GREATER than anything we could possibly need even with shot bearings
2) If oil is not viscous enough it will definitely cause moments of oil starvation at the bearings because viscosity is what levitates the bearings off the crank
3) If oil is TOO viscous, it will cause higher pressure indication, BUT coupled with the massive pressure from our pumps this is a nonissues because it will be constantly forced onto bearing surfaces, and when it's there, even LOSS of oil pump pressure will not harm the engine because the increased oil viscosity allows it to sustain the crank/etc for longer on its own.

ROG100

H,
The difference is in the ambient temperature IMOO.
We are already at 100F here in DFW and possibly that equates to a higher engine temperature over say a 70F ambient.
Higher operating temperature = lower viscosity = lower pressure
These are all questions in my head and not statements of fact.

You still got snow in Seattle?? 8>)
Roger

heinrich

Hi Roger, well I noticed that at 60deg in AK it felt like 100. But returning here I noticed 60 is COLD. But somehow I don't think a Porsche engine or its oil cares. 60 is 60.

anonymousagain

Not sure if this helps, but I've done some non-scientific Blue Car 16v to SATA 32v comparo...

Hot temp (my concept of ~78deg day after highly spirited mountain road 20-80mph, 20+min):

Blue Car: M1 15w-50; Temp slightly above 9:00; idle 2.5bar; 3k+ 5bar
Blue Car: RotellaT 5w-40; Temp slightly above 9:00; idle 2+ish bar; 3k+ 5bar

SATA: M1 15w-50; Temp slightly above 9:00; idle 3+ish bar; 3k+ 5bar
SATA: RotellaT 5w-40; Temp slightly above 9:00; idle 2.5bar; 3k+ 5bar

Observations:
- same OP behavior if Blue Car M1 and SATA RotellaT
- both cars, OP comes off "warm-up" 5bar noticeably sooner with RotellaT
- SATA lifters seem minutely quieter at idle with M1, but just minutely
- no discernable Temp differences with either oil, in either car, even on some 85+deg days of heavy stop/go

Makes me "feel" like The Blue Car likes 15w-50 and SATA likes 5w-40. Both are quality oils, so I'm okay with that... considering trying Syntec 5w-50 though, just to see if it'll yield the best of both.

Good luck!!

ROG100

So does ambient temp effect operating temp of car? yes or no?

hacker-pschorr

It should heat up quicker - should not run any hotter assuming your cooling system is in order.

There is my issue again - I have no oil cooler yet

heinrich

Only in that it may affect the ability of the radiator to maintain the engine's optimal temperature. But if you've got air flowing across the radiator, I don't think it does.

ROG100

OK - Then it would appear that the reduced oil pressure in my case is directly related to oil viscosity.
I went from a 15 to a 5 and according to what I have read I would see a differnce in pressure due to the thinner oil particularly at higher operating temperatures.
5 having a viscosity of 4cSt and 15 6cSt at 100C
However now the second part of the oil number comes into play - 40 V 50.
This means that the 5W 40 will have a viscosity of 40 at operating temperature and likewise the 15W 50 will have a viscosity of 50 at OT.
This is due to the added polymers preventing early thermal breakdown.
So this tells me there is not a lot of difference between 5W 40 & 15W 50 in viscosity terms.
SO WHY HAS MY PRESSURE GONE DOWN - head hurts.

the flyin' scotsman

Absolutely...........while we don't have the extreme heat of Texas we have the complete opposite in the winter. At ambient temps well below zero engine warm up times are long and operating temps are seldom reached. During spring/summer engine and transmission temps go to 'normal' levels and above dependant on ambient temp, usage of a/c and driving conditions (speed etc).

The higher the speed, the warmer the ambient temp and usage of other power robbing accesories contribute to higher operating temps.

For the oil viscosity discussion I find that as the oil ages so the viscosity seems to be reduced as does the pressure. Fresh oil aleviates these conditions.

hacker-pschorr

Here is what my owners manual states (bold is from the manual):

I have no idea what the 32V manual says but I'm going back to something on this list. My local NAPA has 20w-50 Royal Purple (what is in my track car) on sale for $6 per quart. My car has never been drivin below 32 degrees much less 5 degrees.

Can someone post this same data from a 32V motor just for comparison sake?

What I'm finding very interesting is a local VW guru informed me ?w-40 was not to be used in my 16V VW motor unless I have an oil cooler. That this engine (the VW) needs someting W-50 (without the cooler). I know, totally different engine, but interesting non the less.

sharkmeister85

My understanding is that the first number only refers to "cold" viscosity and has no bearing on viscosity at normal operating temperatures and higher.
Glenn

anonymousagain

Royal Purple - my Dad is an RP believer and runs it in everything (work trucks to 800hp blown rods), in fact he's now a dealer --> which urged me to inquire with RP about a comparable choice to RotellaT 5w-40, since they didn't list anything on web less than 10w-xx (ie, 0w-xx or 5w-xx).

Reply and graph:

I do plan on trying the RP XPR10w-40 Racing, but I found it interesting that the graph was for non-XPR10w-40 (the "normal" RP stuff) and it was equivalent to M1 0w-40. Wouldn't claim a direct correlation though, where RP 10w is = to M1 0w --> so RP 20w is = to M1 10w... but it is curious whether RP 20w-50 is in fact closer to a 10w-xx, which would make it a 10w-50 full synth.

Dunno

svp928

Much as I like Mark K, I'm going to have to throw some more water on his Mobil 1 fire- I talked with several of my customers in racing, and asked about what type and weight of oils they were using. Here is what they told me: 2 teams which field engines making 800+ hp at 9500+ rpm, run a 70% duty-cycle for 2 to 3 hours at a time- M1 synthetic 0w-20!! (0w-20, not a typo). Engines are designed with clearances and bearing composition to take advantage of this. Some qualify with a straight 0w oil...

Another prominent team in open-wheel racing uses 0w-40 in an engine that runs 10-11K rpm for a couple hours, making 650+hp...This particular team uses M1 synthetic, and the engine manufacturer recommends it. Again, the engine was designed to use this type of oil. They all run oil temps in the 230-260 deg F range, and use the synthetic M1 because it does NOT break down at high temps and shear loads, as Doug Hillary has reiterated.
I guess my point is, Mark may have had problems with M1, but it does not mean something is wrong with the oil. Our engines were not designed or clearanced for an 0w-20 racing oil, and it probably would not work for us, but I have used M1 15w-50 in my car for the last 11 years, on track and off, never had a problem. But, as has been mentioned, all engines are not the same- very small differences in clearances can make a big difference in hot oil flow, and it may mean your oil p light comes on, or doesn't. Hacker, for your sake, I'm hoping this why you are seeing your light come on, not because the bearings are gone! Your engine's clearances may be just enough to make 5w-40 show low pressure at idle.

Sorry Mark, I agree with Doug- Mobil 1 is not the enemy....

Steve