Oil Pressure Does Not Equal Lubrication
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Well if thats the case it would seem that some laws of physics need to be rewritten. Beam me up Scotty.Quote:
That's a big ten-four there good buddy.
Ha Ha very funny. Now about those pesky laws of physics??? Besides I'm not riding in no stinkin alien spacecraft. Enterprise come in.
Pressure doesn't increase in engines as they age because the oil pump doesn't increase in efficiency.
Pressure does NOT mean increased flow. Ever turn on a faucet connected to a hose, then kink the hose? The pressure builds, but, if the kink is sufficient, you can have very little, or even zero flow. If you have molasses coming out of the spigot at 60 psi, it won't flow through the hose as fast as water at 60 psi.
The arterial system of an animal is a good example of what Dr. Haas is talking about. Plaque narrows arteries, and in order to keep the same post-plaque flow as you had before the plaque built up in the artery, you must either increase pressure or DECREASE viscosity.
As we cool patient's blood in cardiopulmonary bypass, it gets thicker, and the pressure required to flow a given volume per minute increases. In a cooling body, that is OK, because the metabolic rate is decreasing. In an engine, that is NOT OK, as the stress of fuel exploding doesn't decrease with cooler temperatures.
This all tells me that to supply the needed flow rate at a given pressure, the thinnest oil that gives adequate protection is the correct strategy to follow on both ends of the spectrum. When cold, the less viscous an oil, the more flow provided at a given pressure. When hot, the less viscous oil flows more unit volume % at a given pressure, which provides more cooling of hot parts.
Pressure does NOT mean increased flow. Ever turn on a faucet connected to a hose, then kink the hose? The pressure builds, but, if the kink is sufficient, you can have very little, or even zero flow. If you have molasses coming out of the spigot at 60 psi, it won't flow through the hose as fast as water at 60 psi.
The arterial system of an animal is a good example of what Dr. Haas is talking about. Plaque narrows arteries, and in order to keep the same post-plaque flow as you had before the plaque built up in the artery, you must either increase pressure or DECREASE viscosity.
As we cool patient's blood in cardiopulmonary bypass, it gets thicker, and the pressure required to flow a given volume per minute increases. In a cooling body, that is OK, because the metabolic rate is decreasing. In an engine, that is NOT OK, as the stress of fuel exploding doesn't decrease with cooler temperatures.
This all tells me that to supply the needed flow rate at a given pressure, the thinnest oil that gives adequate protection is the correct strategy to follow on both ends of the spectrum. When cold, the less viscous an oil, the more flow provided at a given pressure. When hot, the less viscous oil flows more unit volume % at a given pressure, which provides more cooling of hot parts.
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Insert "necessarily" before equal and all your anxieties will be tranquilized.
One must remember that most peoples' perception of pressure is the oil pressure gauge. Low pressure in itself may not be a bad thing, but low pressure in your oil system can be. First there must be a cause. While this could be many things, some can mean less lubrication. For instance, if there becomes a point in the oil system where oil pressure is being relieved, such as a faulty pressure relief valve, excessive clearances, ect, that means that more oil will take this path instead of the more restrictive paths, such as bearings.
In this case low pressure does equal less lubrication. It may not be a direct correlation, but it's real. Saying that lower pressure does not equal less lubrication is misleading when in the context of engines. While I agree with your argument, I think this thread will just lead to people thinking low oil pressure is no big deal. Not good!
In this case low pressure does equal less lubrication. It may not be a direct correlation, but it's real. Saying that lower pressure does not equal less lubrication is misleading when in the context of engines. While I agree with your argument, I think this thread will just lead to people thinking low oil pressure is no big deal. Not good!
Notice how I used the phrase all other things being equal. I Stand by my comments. Rickey
If people pay attention to the context, there shouldn't be a problem. The crux of the matter is that higher oil pressures that come with using higher viscosity oils does not equal more flow or better lubrication in a normally functioning engine.
Anyone remember those sprinkler hoses, that have little holes along them to let a bit of water out? If you reduce the flow at the inlet enough, all of the water leaks out before it reaches the very end. Would using a thicker fluid at the same flow rate restore the flow to the far reaches of the hose, or would the increased resistance to flow along the hose be too much to allow the far end holes to keep flowing?
I don't usually post here, but I agree with Rickey. It sounds like the laws of physics are being repealed. To equalize things, let's assume a GM V8 with a 30 weight oil with an oil temperature of 100C. Under ideal conditions, neglecting heat loss, friction losses, etc, pressure is built due to resistance to flow. The idea here is to maintain an adequate flow rate across the bearings. Again, for the sake of argument, let's assume the engine builds 50 psi of oil pressure at a 3000 rpm cruise. Also for the sake of argument, let's say the pressure relief on the pump is 65 psi, a typical high performance pump. The only resistance to flow is the bearing clearances. Wider clearances mean more flow. Wider clearances also mean lower oil pressure. Since this is a positive displacement pump, the same amount of oil is moved whether the oil pressure is 10 or 60 psi at 3000 rpm. However, at 10 psi, I doubt any oil is getting past the first bearing journal. (All else being equal, I would use a high volume pump in an engine with wider than normal bearing clearances.)
In this case, again with all other things being equal, 50 psi would generally indicate healthy bearings and 10 psi means rebuild time.
As to whether or not there is value to a high volume oil pump, as long as it is not opening the bypass, more oil at a higher pressure will be delivered to the bearings. All else being equal, the bearings will get better lubrication. Even if the pump is in bypass, what is the problem with that? You will still deliver all the oil the engine can flow at 65 psi.
No one rebuilds engines due to high oil pressure at operating temperatures.
Are there advantages to higher/lower viscosity oils? That is a different question.
In this case, again with all other things being equal, 50 psi would generally indicate healthy bearings and 10 psi means rebuild time.
As to whether or not there is value to a high volume oil pump, as long as it is not opening the bypass, more oil at a higher pressure will be delivered to the bearings. All else being equal, the bearings will get better lubrication. Even if the pump is in bypass, what is the problem with that? You will still deliver all the oil the engine can flow at 65 psi.
No one rebuilds engines due to high oil pressure at operating temperatures.
Are there advantages to higher/lower viscosity oils? That is a different question.
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How so? Especially when followed up by this:
Let's say I have 22 lbs at idle with a 20 weight. I have 40lbs with a 40 weight. I have the same flow in spite of higher pressure. This repeals no laws of physics.
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Well, all other things cannot be equal. If the pressure is higher then either the volume or the viscosity must be altered. You do have an unavoidable triangle there. The false assumption is that just because you have good pressure that you're assured good flow and good lubrication. Pressure is a byproduct (of unqualified worth) and not a facilitator of flow.
Unfortunately you are expecting pressure to reflect flow when in fact the action of the oil pump is to move volume, pressure is a product of resistance to flow.
You can have excewllent indicated pressure and have restricted flow to a bearing and not know it until failure occurs.
In the winter with 15w40 HDEO and at temperatures of -30° in a Ford Powerstroke I have instant pressure. Yet there is a nauseating noise when the engine starts and this noise of loud rattles and rocks in a coffe can continues for 5 or more minutes despite the block heater. Does a high oil pressure shown on a gauge indicate lubrication to the bearings? Heck no.
I would rather have a much lower indicated pressure and have that noise and wear go away with real flow to the lubricated parts. How can that be achieved??
You can have excewllent indicated pressure and have restricted flow to a bearing and not know it until failure occurs.
In the winter with 15w40 HDEO and at temperatures of -30° in a Ford Powerstroke I have instant pressure. Yet there is a nauseating noise when the engine starts and this noise of loud rattles and rocks in a coffe can continues for 5 or more minutes despite the block heater. Does a high oil pressure shown on a gauge indicate lubrication to the bearings? Heck no.
I would rather have a much lower indicated pressure and have that noise and wear go away with real flow to the lubricated parts. How can that be achieved??
This has gotten interesting. But I do understand every word the good Doc wrote.
Bryan, it sounds like you need a big oil pan heater. A block heater does a limited amount of good for the oil in the pan.
The crux of the statement like - higher pressure equals more flow, all things being equal, is beginning to be pointed out. Just how is the pressure to change, especially if "other" operating factors are to remain equal?
Some changes that have been mentioned here that could lead to increased oil pressure are an increase in viscosity, increased restrictions in oil passages...which in my mind don't equate to increased flow. Increasing the engine's/oil pump's speed will first increase flow and with line restrictions remain nearly constant (the exception possibly being from bearing bleed-out due to shearing - to what degree?), thus allow for a build-up of pressure.
Some changes that have been mentioned here that could lead to increased oil pressure are an increase in viscosity, increased restrictions in oil passages...which in my mind don't equate to increased flow. Increasing the engine's/oil pump's speed will first increase flow and with line restrictions remain nearly constant (the exception possibly being from bearing bleed-out due to shearing - to what degree?), thus allow for a build-up of pressure.
Wrong, the oil pump pressure relief valve opens quite often in many engines. Most service manuals will tell you the RPM that maximum pressure should occur given a viscosity of oil and oil temperature. Most engines, even when at operating temperatures, will open the oil pump pressure relief valve anytime your acceleration forces the engine above the RPM defined above. At normal highway speeds, the RPMs are generally low enough to be below the threshold.
However, during the period the engine is coming up to temperature, even at moderate highway speeds, many engine's oil pump pressure relief valve will be open.
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