allegretto

This is not ascertainable from the problem as stated. However if we assume that the 40 weight and 50 weight have exactly the same heat transfer characteristics (not an unreasonable assumption) you are not correct, no way no how. Faster flow to the heat "sink" (radiator) will mean faster heat dissapation, regardless of the refrigerant, period.

This is not an analagous example for many reasons, not the least of which is the discontinuity of flow.



The engineers at Porsche apparently do not agree. Your above incorrectness notwithstanding I would tend to give the nod to the Porsche folks. After all they did design the engine and I would think they know at least as much about its characteristics as you do. After all, if I remember correctly you haven't even driven one?

One more point, 4500 mi on 0 W 40 and still haven't added a drop.

texas911

I call BS on this. If that were the case, then racers wouldn't be using something as viscous a water to cool their engines. The flow of cooler liquid far far outperforms slow thicker fluid when trying to get rid of heat.

allegretto

Of course. We'd use something much more viscous than water.

The mistake he's making is comparing finite exposure time with no heat sink (finger over a candle) to a countuous flow closed system with a sink (oil or water cooling). This solution would not get past a sharp high-school student let alone the engineers that Porsche hires.

1999Porsche911

Physics tells me I am correct about the speed of a fluid, it's density and the ability to absorb heat, so if you disagree, you'll have to take it up with the science commnity, and not me. You do know too, that the faster a liquid moves with resistance, the greater the temperature of the liquid will become?

As for trusting Porsche more than God himself.......well, I guess that is your choice, but I wonder why there are oil leaks and oil burnng and seal problems in their engines using the 0W40. Seems to me that many who have switched from the Mobil Water have reduced or eliminated these problems, altogether. Many on this forum, as a matter of fact. And their valves are quieter on startup. I wonder how that is possible?

And then there is some people reading into things that are just not there. Porsche DOES NOT state not to use 15W50 in their engines. As a matter of fact, they used to fill their cars at the factory with this weight oil. It just so happens that it is no longer on their approved list. If you want to interprete this list as a statement that 15W50 is not good for your engine, then I guess you would also have to believe that the godlike engineers at Porsche made a great and costly mistake? You just have to figure out whether it was then, or now. Either way, they DID make a mistake.

1999Porsche911

That is because water is denser than oil. Don't they have science classes in Texas? If speed was not an issue, see what happens when you double the speed of your water pump. If a fluid absorbs less heat, it cannot dissipate as much.

allegretto

Your Physics in Your Universe perhaps. But here in this Universe I'm afraid that Science is most assuredly not on your side. Heat dissapation characteristics are very well known. Please take this question up with an engineer familar with these issues. There is no point continuing this conversation at this level. You are incorrect and your analogy demonstrates your lack of understanding.

You insisting otherwise only worsens your situation. Faster cycling, within reasonable limits means faster cooling. Heat build up in flow is likely little or non-contributory at these levels. Please re-aquaint yourself with characteristics of cooling systems before your hole becomes deeper.

Sorry

allegretto

You once again do not understand. Each unit of fluid does absorb less heat, of course. But more fluid goes by the heat, increasing the energy steal and more fluid goes through the sink, increasing the off-load of energy.

Please stop now. You are hopelessly underwater and repeatedly have demonstrated your lack of understanding.

1999Porsche911

Ok, I will type slowly so you have a better chance of understanding. Let's break it down:

1. The slower a liquid flows, the more heat it will absorb. Agree? (If not, stop here now)

2. The less heat absorbed by a liquid means that more heat was left behind at the source. Agree?

3. The faster a liquid travels in a closed system without an external heat source, the greater the tempertaure of that liquid will become. Agree?

4. A denser liquid, such as water over oil, has the ability of absorbing more heat. Agree?

5. Number 4 is why they do not use 100% oil in the cooling system. Agree?

6. The amount of heat removed from a liquid by a radiator is directly related to how hot the liquid is in a contant ambient temperaure and air movement situation. Agree?

7. If a less dense liquid absorbs less heat from the source than a denser liquid, the source will remain hotter when using the less dense liquid. Agree?

8. There is an optimum speed at which a liquid can move and properly balance it's task of both absorbing heat and releasing it to the air through the radiator. Agree?

9. The slower a liquid passes through the radiator, the more heat that will be removed from the liquid. Agree?

The fact is, if you move a liquid too fast, it will not absorb as much heat and will not dissipate as much heat through the radiator leaving the source (engine in this case) hotter than it needs to be. The liquid's density is exactly why heat is dissipated faster when you run straight water in your cooling system.

Therefore, your statement of "more fluid goes by the heat, increasing the energy steal and more fluid goes through the sink, increasing the off-load of energy" is fundementally wrong as the faster the liquid moves, the less heat it will absorb from the engine and the less heat will be removed by the radiator.



There is also a downside to running a liquid too slow.

allegretto

You are so confused and your suppositions are in places wrong in fact or wrong in particular practice that there is no point in continuing. There is too much you don't know and you are now trying to compensate by just throwing up verbiage. So I will stop right here. You obviously do not undersand heat transfer in a system.

Good thing you don't attempt to design engines or refrigerant systems however, but if you did, you would not be writing what you write. Please speak to someone who does...I'm out, this is boring.

1999Porsche911

So, since you obviously know more than me, please state which of the statements I made are NOT true. Should be funny for all of us to see which ones you disagree with and why, even though they are based in fact, they must not be true?

But, I suspect you will simply continue to challenge me by making general statements rather than having to commit to specifics. Most see right through that approach.

eclou

Water pumps will cavitate past a certain rpm depending on the blade design. Has nothing to do with keeping flow at a certain rate. Cavitation leads to diminished flow rates.

Faster flow will always have a improved ability to remove heat since the exposed surface area at the interface is effectively increased. Same reason why old A/C units would freeze over the evaporator if you kept the fan on too low - not enough flow to transfer the temp differential. The air itself coming out the vent wasn't necessarily any colder up to freezing over, but the evaporator temps were dropping. Same principle of wind chill and wine chillers.

allegretto

I'm going to try to explain, but if all you are going to do is continue to argue this cause, I'm not up for it. And I do apologize for my abrupt tone but you are being a bit thick about this. Here goes;

1) up to a point yes, but depending upon specific characteristics of the fluid, it can only carry so much additional heat

2) Agree

3) Not sure I understand the statement. In an auto the coolant system is effectively closed, the engine IS an external heat source. If you are speaking of frictional heat, then yes but in auto systems those contributions are negligible.

4) Nope, much more complex than simple density. Heat conduction has to do with many possible factors with a given fluid

5) Nope. Water is used because a) it has to vent and water is one of the few substances that is completely safe to do so; b) it is cheap and plentiful; c) it is an excellent solvent and therefore very additive friendly. d) it is a very good conductor of heat.

6) Several other factors at play here. Surface area presented, temp of secondary coolant and of course the conductive properties of both the coolant of the engine and the radiator material and the conductivity of the radiator's coolant. Complex issues at this level. But if you are tring to say that generally the hotter the primary coolant the more a radiator can sink from it, I agree to a point dependant upon the other factors I've mentioned.

7) As I noted above the "density" issue is too simplistic, but if you are saying that the less heat conducted away, the hotter things get...well, yes.

8) Yes, and that "speed" s dependant upon many factors in the system.

9) Depends upon speed of the two coolants as well as surface area of the radiator its conductivity and temps of the coolants.

In theory one can easily solve for many issues of conductance, of heat or other forms of energy, electricity for example. In practice these issues become even more devilish however. I'm afraid you have tried to boil down (pun intended) a complex topic a little too much and coupled this with a couple of incorrect notions about energy flow. That's what engineers make a living doing, taking simple theorhetical issues and go about the difficult task of making them work in the real world.

In theory there is no difference between theory and practice...

Doug Hillary

Hello,
for obvious reasons I don't particularly want to post here but the posts of 1999Porsche911 on lubricants should be viewed with great trepidation. He often makes comments and statements that are simply wrong, they often betray his lack of understanding of the principles of engine lubrication and lubricants and most cannot be substantiated

As an example 1999Porsche911 said;
"That is not true. (BTW: the W indicator is only for cold viscosity). The number before the W is it's flow rate NOT UNDER PRESSURE) at 0F. The second number, without the W is it's flow rate at 212F.

Under pressure, especially using a positive displacement oil pump, the flow of a 15W and a 0W oil is virtualy the same at 20F, so unless you start your engine in a temperature less than 20F, there is no flow benefit to using 0W. However, because the non pressurized flow rate of the 0W is greater than a 15W oil as it begins to cool, you lose more oil film on engine parts and oil in the lifers, etc, with the 0W simply because of gravity. That is why, many engines that sit with a thin oil for several days will make lifter noises more than engines that have a thicker oil."

Much of this can be disputed and his later posts contain much more misinformation!

IMHO Porsche owners should always use Porsche Approved and Listed oils - most of the 100 odd lubricants of various Brands are either 5w-40 or 0w-40 viscosities with only one 5w-50 viscosity lubricant being on their Approved List
Sadly in the USA Mobil 5w-50 is either unavailable or hard to obtain - it is on the Porsche Approved List because of its rather unique qualities - viscosity/Viscosity Index - related

As for lubricants and turbochargers it is significant that only a 0w-40 oil is Approved for use in the twin turbo Cayenne regardless of use and temperature
It is the quality and formulation of the lubricant that has the greatest influence on turbocharger life. Many non Porsche turbocharged engines successfully use 0w-20 or 0w-30 recommended lubricants. The trucking Industry uses 15w-40 or lower viscosities (5w-30, 0w-40 & 5w-40) and have successfully done so for a number of decades - in high power/torque, high speed and high boost turbocharged engines

For maximum design "first life to rebuild" always use the lubricants Approved by the engine's manufacturer. The Porsche factory's engine fill (except for the Cayenne V6 - where the most common viscosity is 5w-30 -VW Spec 503.00 or later) is either a 0w-40 or a 5w-40 - for all World markets

Regards

texas911

You guys should go and do a drag race with his Z06 instead.

mastiffdog

Here we go again...

The usual suspect showed up in this thread. It's sure to become a humdinger!