If thick oil offers more protection, then isn't cold oil best?

[OVERKILL]

It's never fully "decoupled". PD pumps with a spring loaded pressure relief do keep building some pressure and increasing output volume, as shown in the post above. You even pointed that out that aspect in post 97. It rolls over pretty good, but it's still building output volume and pressure.

Of course, once the relief is overwhelmed, system pressure, and volume, will continue to rise. My point is simply that the direct relationship between each rotation of the pump and the volume of oil entering the engine decouples, as some of that volume now exits the relief, this is observable on your graphs, where the very straight line folds over and the curve becomes much more gradual. The relationship still exists, but it is no longer the direct relationship it was prior to the role of the relief entering the picture.

 

[ZeeOSix]

Yes, but the relationship between the each rotation of the pump and the amount of oil entering the engine is decoupled was my point. It's a very simple relationship without the relief in the picture. Once you include the relief, then you have to factor in relief behaviour, like, as you noted, its varying capacity as it opens (cracks) until it hits full capacity (fully open), which makes the conversation a bit more complex.

Yes, it's "decoupled" in terms of a direct output wrt the pump's displacement and RPM. But as shown above, even in pressure relief the output volume and pressure still increases some. And the colder the oil is, I'd venture to say the worse the output pressure control there would be because the relief circuit would be overwhelmed easier. Let's throw in pump slip and efficiency to make it even more complex, lol.

On my Jeep for example, with 0W-40, it goes onto the relief (~65psi) on a below freezing cold start, but observed system pressure doesn't rise beyond relief pressure (so volume is being shunted, but that volume is able to be handled by the relief, so observed pressure doesn't increase) unless I increase engine RPM to the point where I overwhelm it. This is different from the SBC behaviour I described where the relief is overwhelmed immediately.

It's just another dimension to the discussion, my apologies if I wasn't sufficiently clear in how I was trying to frame it.

Sure, every engine + pump combination is going to behave in a certain way. Melling's aftermarket pumps also try to focus on better pressure relief control vs the OEM pumps by trying to make the relief valve and circuit as efficienct as possible for a mechanically spring relief valve.

 

[ZeeOSix]

Of course, once the relief is overwhelmed, system pressure, and volume, will continue to rise. My point is simply that the direct relationship between each rotation of the pump and the volume of oil entering the engine decouples, as some of that volume now exits the relief, this is observable on your graphs, where the very straight line folds over and the curve becomes much more gradual. The relationship still exists, but it is no longer the direct relationship it was prior to the role of the relief entering the picture.

Of course any time the pump is in relief whatsoever, it no longer has the direct linear volume output and corresponding pressure vs RPM. Thought that was understood without explaination. But @cheesepuffs2 asked how can a PD still build pressure and volume if its in pressure relief in post 94, and that's what led to this PD pump discusson, with the answer being that the pump can't perfectly control pressure and volume with a spring loaded pressure relief valve.

 

[cheesepuffs2]

with the answer being that the pump can't perfectly control pressure and volume with a spring loaded pressure relief valve.

Like most everything else here, isn't the answer now this black and white, and really more like "it depends on the relief valve in question"? If the relief valve is large enough to shunt off enough pressure, then wouldn't it remain cracked enough to maintain pretty good control of the pressure? I fully understand that in the SBC example, the relief value is insufficient to do that, but if anything the SBC example just shows that there are outliers and circumstances that create variation from powertrain to powertrain.

 

[ZeeOSix]

Like most everything else here, isn't the answer now this black and white, and really more like "it depends on the relief valve in question"? If the relief valve is large enough to shunt off enough pressure, then wouldn't it remain cracked enough to maintain pretty good control of the pressure? I fully understand that in the SBC example, the relief value is insufficient to do that, but if anything the SBC example just shows that there are outliers and circumstances that create variation from powertrain to powertrain.

I'd bet most PD oil pumps with a spring loaded pressure relief valve are going to have very similar operation as those Melling pump curves. It's just a simple spring loaded check valve. I talked to Melling about their pumps, and they said they have tried to make the pressure relief valve as efficient as they can, so their pumps have less creep than the OEM oil pump. But they still have pressure and volume creep after the pressure relief valve starts to open. Melling has been in the oil pump business for decades ... one of the first.

The only way you could make a PD pump have absolutely perfect pressure control at some designated point inside the engine is to have it computer controlled with a closed-loop pressure sensor placed down stream of the pump.

 

[cheesepuffs2]

I'd bet most PD oil pumps with a spring loaded pressure relief valve are going to have very similar operation as those Melling pump curves. It's just a simple spring loaded check valve. I talked to Melling about their pumps, and they said they have tried to make the pressure relief valve as efficient as they can, so their pumps have less creep than the OEM oil pump. But they still have pressure and volume creep after the pressure relief valve starts to open.

The only way you could make a PD pump have absolutely perfect pressure control is to have it computer controlled system with a closed-loop pressure sensor placed down stream of the pump.

But in Overkill's Jeep example, the relief valve can sufficiently bleed off excess pressure is basically any normal operating condition, so wouldn't the spring only open as far as it had to, and then at a certain point remain merely cracked and stabilize the pressure across the curve? Same concept as what you're saying would need to be computer controlled, except it's a mechanical spring, and would operate similar to a turbo wastegate.

 

[ZeeOSix]

But in Overkill's Jeep example, the relief valve can sufficiently bleed off excess pressure is basically any normal operating condition, so wouldn't the spring only open as far as it had to, and then at a certain point remain merely cracked and stabilize the pressure across the curve? Same concept as what you're saying would need to be computer controlled, except it's a mechanical spring, and would operate similar to a turbo wastegate.

In post 100, Overkill said ... note the bold part:
"On my Jeep for example, with 0W-40, it goes onto the relief (~65psi) on a below freezing cold start, but observed system pressure doesn't rise beyond relief pressure (so volume is being shunted, but that volume is able to be handled by the relief, so observed pressure doesn't increase) unless I increase engine RPM to the point where I overwhelm it. This is different from the SBC behaviour I described where the relief is overwhelmed immediately."

Could be that the pump displacement vs RPM is lower than compared to the LS pump. So it takes more RPM to get the volume to start getting it into relief pretty good to where it can been seen. Like said, the system as a whole (engine oiling system, pump design & relief setting, oil viscosity) will determine the operating characteristics as a system.

If you look at the LS pump pressure vs RPM curve above, you can see how the pressure builds exponentially until around 3000 RPM when the pressure relief valve starts to open. That pump puts out quite a bit of volume per rev. If the pump puts out less volume per rev, it's going to take more revs beyond the initial opening of the valve to overwhelm the relief. But just the physical aspect of the mechanical design of a spring loaded pressure relief valve, it can't provide a perfectly constant pressure control because as it starts opening and relieving it needs more and more pressure to keep opening it. So that shows up as a slight pressure increase (and volume output) as the pump increases in RPM while in relief. If the relief valve does open enough to "bottom out", and the RPM then keeps increasing, the relief valve can really became overwhelmed. That's not a situation a PD should be allowed to get to.

 

[ZeeOSix]

Yeah - all over the place - mention of a water tower?
That’s height X 0.052 X 8.33 for pressure at the base. Call that the pump pressure - from there pipe ID is the big parasite - length is decay in psi/foot, and then each bend, etc…

A water system feeding water to a bunch of houses needs to be designed properly to ensure an adequate volume of water gets to all end points. Just like an oiling system needs to be designed to ensure the proper oil volume gets to all required points in the engine. In both systems, the pressure source (water tower or pump) needs to be designed right, as well as the distribution system, to produce the right volume. More pressure at the source means more volume sent down the fixed flow system ... nothing changes that basic law of fluid dynamics.

 

[FTTSHO]

Cold engine oil (no matter what xW-xx it is) is still too thick for engines even while it’s cold.


Using a 50 or a 60 grade oil on any regular passenger vehicle is overkill, because it will just take longer for the oil to exit bearings, and this isn’t a benefit at all. If the oil is too thick for the application, it takes longer to escape bearings, and the longer it takes, it only means the heat in the bearings won’t be transferred to the oil quickly enough, which isn’t ideal.

It’s all about finding the right balance, and on regular cars that never sees excessive oil temps, the oil viscosity the manufacturer recommends is more than adequate.

For example, if 0w-20 was really too thin for engines, it would mean the oil would escape the bearings too quickly because the oil pump can’t keep up, and if this actually happens, a spun bearing will be the result.
It would happen in the blink of an eye. If the crank shaft journals ever touches the bearing, it’s over.

The wear we actually see on bearings are from carbon/metal contaminations in the oil, not from the bearings itself making contact. A thicker oil wouldn’t prevent contaminants from wearing bearings.

Using the manufacturer recommended oil for the right application is perfectly adequate. No need to over think it. And also, changing the oil on a reasonable OCI is the best practice, because removing contaminants from the oil is the only thing that will prevent wear on bearings, not just switching to a thicker oil.

The best practice isn’t using 40 weight oil because you feel the 20 weight the manufacturer recommends for your engine is too “thin”. If it really was too thin, you wouldn’t see more wear on bearings, your engine will just lock up at some point. This just does not happen.

There are millions of vehicles on the road that sees nothing but 0w-20 and regular point a to point b driving, and they are all running fine. Engine failures do not happen because of thin oils, it happens because people don’t change their oil enough, and contaminants in the oil start wearing things down.

There are however rare cases were some engines do fail early, even after using the manufacturer recommended oil viscosity, but I guarantee the engine didn’t fail because of changing the oil too often or because too thin of an oil was used, it failed because of a defective part, and bad QC from the factory.

 

[kschachn]

People really try hard on this one.

A proper 40-grade is perfectly fine.

 

[RDY4WAR]

Contaminants are not a primary cause of bearing wear. Excessive heat, torsional vibrations, corrosion, and (of course) loss of lubrication are primary causes of bearing wear. Contamination is a secondary cause. For example, contaminants often greatly impact aeration/foam prevention which can result in bearing cavitation (loss of lubrication). If you have sufficient contaminants to actually impact bearing wear, you have bigger problems to worry about. It takes a lot to reach that point which is why we have condemnation limits on contaminants. Most won't come remotely close to that condemnation, not in 25k miles much less 5k miles, with a healthy engine.

 

[ltslimjim]

Hot oil is happy oil. Additives, like most things in chemistry, become more reactive with heat. Different additives, including different variants of the same additive, peak at different temperatures. Oils like HPL Euro and Bad Ass Racing oils don't reach peak friction coefficient until 300-305°F.

Thicker is usually (almost always) better to an extent in terms of wear. There is a point where you can overheat the bearings, resulting in fatigue of the soft metals, due to a combination of decreased oil flow and increased hydrodynamic friction. In some engines, high enough viscosity can break the oil pump shaft. Higher viscosity also tends to increase the pressure drop across the oil filter media which makes it less efficient and more likely to have a failure.

Made me think of this video…

Amsoil’s chemistry department guy talking about this subject; in the very beginning of the video.

 

[ZeeOSix]

Contaminants are not a primary cause of bearing wear. Excessive heat, torsional vibrations, corrosion, and (of course) loss of lubrication are primary causes of bearing wear. Contamination is a secondary cause. For example, contaminants often greatly impact aeration/foam prevention which can result in bearing cavitation (loss of lubrication). If you have sufficient contaminants to actually impact bearing wear, you have bigger problems to worry about. It takes a lot to reach that point which is why we have condemnation limits on contaminants. Most won't come remotely close to that condemnation, not in 25k miles much less 5k miles, with a healthy engine.

Good oil filtration is important for journal bearings. Lots of engine wear studies show that better oil filtration does indeed reduce wear. And it's mainly the particles that are small enough to get between moving parts that causes the most 3-body wear.

 

[RDY4WAR]

Good oil filtration is important for journal bearings. Lots of engine wear studies show that better oil filtration does indeed reduce wear. And it's mainly the particles that are small enough to get between moving parts that causes the most 3-body wear.

Yes, but define good filtration. Most any oil filter is going to provide sufficient filtration to make wear rates indiscernible within a margin of error and it takes a lot of contaminants to actually move that needle. The bearings will see a good bit more wear from cold starts than it will with contamination unless that contamination is just through the roof. In which case, like I hinted to above, something else is already terribly wrong if that's the case.

 

[kschachn]

Contaminants are not a primary cause of bearing wear. Excessive heat, torsional vibrations, corrosion, and (of course) loss of lubrication are primary causes of bearing wear. Contamination is a secondary cause. For example, contaminants often greatly impact aeration/foam prevention which can result in bearing cavitation (loss of lubrication). If you have sufficient contaminants to actually impact bearing wear, you have bigger problems to worry about. It takes a lot to reach that point which is why we have condemnation limits on contaminants. Most won't come remotely close to that condemnation, not in 25k miles much less 5k miles, with a healthy engine.

What is contamination?

 

[RDY4WAR]

What is contamination?

My definition, in the sense of this discussion, is any particle larger than the MOFT (or minimum clearance under load at the wedge) that is harder than the bearing material.

 

[ZeeOSix]

Cold engine oil (no matter what xW-xx it is) is still too thick for engines even while it’s cold.

Not really ... if it was that detrimental, there would be millions of per-maturely worn out engines that live in very cold climates. That's not the case if they are using the correct W grade oil for their start-up conditions.

Using a 50 or a 60 grade oil on any regular passenger vehicle is overkill, because it will just take longer for the oil to exit bearings, and this isn’t a benefit at all. If the oil is too thick for the application, it takes longer to escape bearings, and the longer it takes, it only means the heat in the bearings won’t be transferred to the oil quickly enough, which isn’t ideal.

Tell that to Ford that specifies 5W-50 on their track focused cars that are also street driven to the grocery store.

For example, if 0w-20 was really too thin for engines, it would mean the oil would escape the bearings too quickly because the oil pump can’t keep up, and if this actually happens, a spun bearing will be the result.
It would happen in the blink of an eye. If the crank shaft journals ever touches the bearing, it’s over.

No journal bearing, even all of them at redline RPM, cumulatively don't pump and leak enough oil and have a side leakage volume great enough for the oil pump to not "keep up".

The wear we actually see on bearings are from carbon/metal contaminations in the oil, not from the bearings itself making contact. A thicker oil wouldn’t prevent contaminants from wearing bearings.

Bearing wear can be severe if the film thickness goes to zero because the viscosity was too low. Go run an engine at the track with too thin oil and see what happens.

The best practice isn’t using 40 weight oil because you feel the 20 weight the manufacturer recommends for your engine is too “thin”. If it really was too thin, you wouldn’t see more wear on bearings, your engine will just lock up at some point. This just does not happen.

Not true ... engine parts can have more wear over time from too thin of oil for the operating conditions, and that engine would never "lock up" or blow-up as a result of more wear. I've seen really worn out engines that still seem to "run fine" from the driver's seat. Even seen engines with rod bearing so worn that they make knocking noises, yet the engine still runs pretty good.

There are millions of vehicles on the road that sees nothing but 0w-20 and regular point a to point b driving, and they are all running fine. Engine failures do not happen because of thin oils, it happens because people don’t change their oil enough, and contaminants in the oil start wearing things down.

Engine failure certainly could happen if the oil was too thin and the operating conditions were harsh. Go put some 0W-8 in your engine and go race it at near redline for 30-40 minutes. In a worse case scenario, the lack of film thickness could overheat the bearings, cause one to lock up and spin, and then lock up the rod to make it crash through the engine block. It can happen. Running and engine with too thin of oil causing the film thickness to go to zero basically falls in to the category of "lack of lubrication".

 

[ZeeOSix]

My definition, in the sense of this discussion, is any particle larger than the MOFT (or minimum clearance under load at the wedge) that is harder than the bearing material.

It's the smaller particles that can get between moving parts that caused the most wear - wear studies show that. Particle larger than that can get crushed and broken up into smaller particles, which in turn then have a better chance of getting between tight clearance parts.

 

[ZeeOSix]

Yes, but define good filtration. Most any oil filter is going to provide sufficient filtration to make wear rates indiscernible within a margin of error and it takes a lot of contaminants to actually move that needle. The bearings will see a good bit more wear from cold starts than it will with contamination unless that contamination is just through the roof. In which case, like I hinted to above, something else is already terribly wrong if that's the case.

Better filtration is better than not ... higher filtration can make a difference over the long run. Every engine wear study concludes that cleaner oil results in less wear. Yes, "dry starts" are also a factor on the relatively soft (sacrificial) bearings, an also is low MOFT conditions. Low and zero MOFT conditions will wear bearing more than any other factor ... hence why adding some more MOFT headroom is benificial. All of it adds up to causing more wear.

 

[cheesepuffs2]

Every engine wear study concludes that cleaner oil results in less wear.

Not disagreeing with this, but then how come we try to push the limits of OCIs? Why not change more often? New oil is clean oil, and a filter can't get the oil cleaner than draining out the dirty oil right out of the sump.