A must read
http://mechdb.com/index.php/Using_hi...sity_oil_myths

 

.....along with:

http://www.supramania.com/aehaas/

 

If ~90% of all engine wear is during cold start up, due to thick oil, wouldn't it be wise to use an oil pan heater every time your car is parked long enough to cool down? Thanks to djb383 for posting that article.

 

Sure seems that way

 

I've wondered the same thing... Along with why pre-lubing systems have not been more popular. I can see the concern with battery draw for hearing systems... But intelligent use of these systems to allow for enough cranking power in reserve seems totally feasible

 

Nothing lasts forever.

Everything eventually wears out.

 

I found one thing that is partially incorrect in the oil 101 section so far. He says

" In fact the relationship between pressure and flow is in opposition. If you change your oil to a thicker formula the pressure will go up. It goes up because the resistance to flow is greater and in fact the flow must go down in order for the pressure to go up. They are inversely related. Conversely if you choose a thinner oil then the pressure will go down. This can only occur if the flow has increased."

If your oil pump is moving let's say 10 gallons per minute of oil, then it should be moving the same amount of oil regardless of its viscosity, but with higher viscosity comes more resistance to move the same amount of oil per minute therefore the pressure increases while the flow stays the same. If you increase viscosity and reduce flow then the pressure will remain the same if you decrease flow proportional to the increased viscosity.

With the design of modern systems it is still better to run thinner oil because of the oil bypass valve which will limit the oil pressure. If you run high viscosity oil you will open the bypass valve at a lower flow than you would with a lower viscosity oil when they both reach the pressure limit of the bypass. He is correct that higher flow provides more lubrication of the bearings so in this case the low viscosity oil is preferred. If though you are not getting any pressure when using the low viscosity oil it means there is too much leakage around the bearings and using a higher viscosity oil will not necessarily fix the problem, only new bearings will.

I'm not an automotive engineer by any means but I am a chemist and do understand fluid dynamics pretty well and this is the only thing I saw that really stuck out as incorrect. It would be correct if the oil was a compressible gas, but not a noncompressible liquid.

 

Try this simple analogy; put a garden hose in a bucket and open nozzle 1/4 turn (good bearings) and time how long it takes to fill the bucket. Now try this with the nozzle full open (worn bearings) and time how long it takes to fill.....hands down the worn bearing (open nozzle) will have more flow. All pressure represents is reserve capability...it has no function other than that. Zero psi is bad because the flow cannot keep up with the demand where it is needed on the higher points of the engine where pressure is NEEDED to lift the oil. If you could measure the pressure of oil at a rod bearings on a healthy engine you might be surprised to see almost zero psi! But you would see enough flow for the bearing surfaces to form a wedge of oil onto the journal so the bearing would act like a surfboard riding a wave.

 

That's only because you're increasing the GPMs.

 

in theory, if you had oil jacks or "pre lubes" on a journal bearing, along with a pressurized oil system, the shaft would never have a chance to touch the journal except at rest. at rest its not moving so you would get close to zero wear. this is common on large compressors and turbines. i think automotive powertrain engineers would probably love to incorporate oil jacks in modern engines, but having engines run forever is not on any shareholder agenda. thats like curing the common cold.

 

Exactly. The was the counter- point I was trying to make to jedijeb.

 

right, and to do that pressure goes down. bernoulli.

 

But above or in one of the links it was stated that the pump's output stays the same regardless of different viscosities. A 1/4" hose (good bearings) and a 1" hose (worn bearings) putting out 10gpm each are going to have very different pressures.

This is how I interpreted it anyways

 

Not true, pumps GPM output is determined by restrictions down stream. As GPM decreases due to restriction pressure inversely increases. The rated GPM of any pump is limited by static pressure on the discharge side. Higher viscosity is the same as higher resistance to flow.

 

That would depend on the type of pump. A centrifugal pump would do this, but a positive displacement pump would not. With a positive displacement pump a restriction would increase pressure while the gpm remained the same, unless the backpressure causes the pump to turn slower which means that its gpm would become less. Things like the water pump in a vehicle are centrifugal, things like a piston hydrolic pump are positive displacement. What would a gear mesh pump like an engine oil pump be? If there is not enough gap between the gears to allow the oil to back flush then the pump will deliver the same gpm at the same rpm regardless of pressure, if there is enough gap that oil can backflush then it could have reduced flow at the same rpm.

The water hose analogy works that way because there is a limited amount of pressure and flow available to the entrance of the hose, which is like the bypass valve on an oil pump, if you restrict the hose flow it will reach a maximum pressure then no more. The point I was making was that as long as you are pumping water through that hose your analogy will hold, but try pumping the same volume (gpm) of molasses through that water hose and what is the difference in pressure? It will be a higher pressure at the same flow rate because of more restriction caused by higher viscosity.