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Old 10-21-2008, 01:33 PM
desertdriver desertdriver is offline
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Quote:
Originally Posted by franka View Post
I've read that synth is superior in cold starts to dino oil because it will cling to the part for 5or 6 days where the dino is 2 to 3 days max, same conditions.

The main and rod bearings in your engine are lubricated by a process called a hydrodynamic wedge. W/o going into the details this process drags the oil with the rotating component and raises the pressure to 8 to 10,000 psi in the bearing preventing metal to metal contact.

So when you motor is running the crank and the rods are supported by the wedge so no metal to metal contact occurs, even under the pressure of a cylinder firing.

But when the engine is cold and started there is bearing material to crank main and rod journals surfaces. There is metal to metal contact until the hydro-wedge is established. And that takes time for the oil to get to the bearings in sufficient quantity. So the better the oil clings the better it lubricates. This is why you should give your engine a minute to get the oil circulated before you put a load the 'dry' bearings.
the clinging of synthetic oil to metal surfaces is purported to be due to the polarity of ester functional group/and metal parts. the PAO's(mobil one and many others) are not polar, hence the explanation doesnt work there. my problem is that I want to see hard evidence that significant amounts cling to the parts, enough to provide a film. Molecualr polarity and the adhesion energies involved are quite low. Im not saying that some tiny amount might not cling, but to say it is sufficient to provide the necessary film thickness to prevent metal to metal contact is a claim that is made only by the manufacturers, and they have a vested interest to make that claim. Without some kind of independent validation it soiunds like exxon denying pollution from its refineries.

what can be said about the better synthetic oils is that they have lower pour points, meaning that oil is likely supplied to the surfaces in need of lubrication faster than dino oils. this means they will have smaller times where NO lubrication takes place.

In all this discussion oils, not additives are discussed. It is know that additives can stick to parts even better than esters, so the base stock of the oil might not be the only factor. Still starting an engine and running it hard are two different situations. As RPM goes up greater demands are made on the lubrication properties for a given temperature. Its obvious that this is a complex subject, and BMW engineers know their cars as well or better than anyone. If they recommend warming the car up before running it hard, they are likely right. Only a fool would disregard BMWs recommendation vs an oil manufacturers advertisement. After all the oil manufacturer has nothing to lose and is driven by the one upsmanship of advertizing, but BMW has a vested interest in taking care of their cars that they stake their reputation on. If your car wears out prematurely, the oil company will not be blamed.
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