0W20 vs 5W30 in 1999 E46 323i

[Trav]

There are so many reasons for main and rod bearing wear that may occur on some bearings more than other on the same crank. Block and crank rigidity, rod flex causing the deformity of the bearing making the lower one tighter and the upper looser. A bunch of other things can be going on, with manual transmissions the thrust bearing can be taking even greater longitudinal stress causing more crankshaft movement. Of course a lot of this also depends on how the engine is operated. This is a BMW inline engine with a long crank. By design it is much more susceptible to flexing then a L4 or V8 even though it has a greater number of main bearings.

Quote:

Due to the length of the crankshaft in an inline 6 engine, extreme harmonic vibrations can happen under high RPM and power use. This causes the block to flex, causing severe main bearing wear or even a broken crank. Reinforcing the block is a necessity for these extreme applications. This girdle kit uses a 1/4” steel plate to bolt on the underside

This is why ideally it would be better if oil pressure could be monitored at each bearing but thats not possible so all we have to go on is the oil galley pressure. IMHO this approach is flawed. A oil meeting manufacturers spec should be use, running 20w in this engine is IMO just asking for trouble that the oil pressure gauge possibly isn't showing till the damage is done.

 

[OVERKILL]

Originally Posted By: turtlevette

There are 2 bypasses. One in the oil pump and one in the filter mount or filter itself.

Yes, but with very different functions. One bypasses oil back to the sump (or the feed side of the pump) regulating system back-pressure, the other just bypasses the filter media when a differential is present to prevent the media from collapsing due to flow limitations. It has very little affect on the system oil pressure.

 

[OVERKILL]

Originally Posted By: turtlevette

I'm glad that you've finally accepted my argument that auto oil pumps are on bypass through most of the operating range. We had some good arguments about a year ago.

I think that was me mostly, not Shannow. And I cited a few examples of engines that weren't on the relief most of the time (like the SBF and a stock SBC) and some that were, like many recent Mopar engines. It seems very manufacturer dependant. I believe the engines with the gyrator-style crank-driven pumps tend to lean on the relief earlier than the older style camshaft-driven pumps from what I've seen. Of course one can swap in an HV pump into either of the two examples I cited and have it on the relief just off idle. But I fail to see the point in doing so given the longevity of those designs operating as intended

 

[OVERKILL]

BTW, this is a great BITOG discussion guys! Let's keep it civil like it has been

 

[Garak]

Originally Posted By: OVERKILL

I think that was me mostly, not Shannow. And I cited a few examples of engines that weren't on the relief most of the time (like the SBF and a stock SBC) and some that were, like many recent Mopar engines.

I can confirm that with the average, stock SBC, too, over the years.

 

[CATERHAM]

Originally Posted By: Trav

There are so many reasons for main and rod bearing wear that may occur on some bearings more than other on the same crank. Block and crank rigidity, rod flex causing the deformity of the bearing making the lower one tighter and the upper looser. A bunch of other things can be going on, with manual transmissions the thrust bearing can be taking even greater longitudinal stress causing more crankshaft movement. Of course a lot of this also depends on how the engine is operated. This is a BMW inline engine with a long crank. By design it is much more susceptible to flexing then a L4 or V8 even though it has a greater number of main bearings.

Quote:

Due to the length of the crankshaft in an inline 6 engine, extreme harmonic vibrations can happen under high RPM and power use. This causes the block to flex, causing severe main bearing wear or even a broken crank. Reinforcing the block is a necessity for these extreme applications. This girdle kit uses a 1/4” steel plate to bolt on the underside

This is why ideally it would be better if oil pressure could be monitored at each bearing but thats not possible so all we have to go on is the oil galley pressure. IMHO this approach is flawed. A oil meeting manufacturers spec should be use, running 20w in this engine is IMO just asking for trouble that the oil pressure gauge possibly isn't showing till the damage is done.

If you're routinely thrashing an 6 cyl M series engine then sure maintain the OP 10 or 15 psi higher than spec' minimum which will still of course be below the oil pump relief setting. So you're increasing your self imposed minimum operational viscosity which may still be achievable with a 20 grade oil if the oil temp's remain low such as during cold winter use. Seemingly off topic but actually related, it also pays to maximize the VI of the oil your using because it will lower the OP at low normal operating temp's for a given HTHSV oil rating. This will allow you maximize the HTHSV of the oil used for whatever minimum OP value you want to use.

 

[Shannow]

Originally Posted By: OVERKILL

Originally Posted By: turtlevette

I'm glad that you've finally accepted my argument that auto oil pumps are on bypass through most of the operating range. We had some good arguments about a year ago.

I think that was me mostly, not Shannow.

Nah, I'll fess up it was in the relief versus controller discussion. As to power output waste on relief http://www.advancedfluidsystems.com/tools-resources/fluid-power-calculator/ 4gpm, 70% pump efficiency, and take a 20psi difference between operation on relief and off relief as a round number, 0.07hp, or 32 watts.

 

[Trav]

Originally Posted By: OVERKILL

Originally Posted By: turtlevette

I'm glad that you've finally accepted my argument that auto oil pumps are on bypass through most of the operating range. We had some good arguments about a year ago.

I think that was me mostly, not Shannow. And I cited a few examples of engines that weren't on the relief most of the time (like the SBF and a stock SBC) and some that were, like many recent Mopar engines. It seems very manufacturer dependant. I believe the engines with the gyrator-style crank-driven pumps tend to lean on the relief earlier than the older style camshaft-driven pumps from what I've seen. Of course one can swap in an HV pump into either of the two examples I cited and have it on the relief just off idle. But I fail to see the point in doing so given the longevity of those designs operating as intended

+1 Some of the SBC had a hard enough trying to make enough pressure to keep the engine alive never mind blow the relief. Buick's with the cam driven pump mounted in the front cover were much worse, they couldn't make enough pressure to lift your hat off when new. When slightly worn bearing wear was a real issue. The crank driven gyrator style tend to make a lot more pressure and is more dependent on the relief as you say.

 

[turtlevette]

Originally Posted By: Shannow

As to power output waste on relief http://www.advancedfluidsystems.com/tools-resources/fluid-power-calculator/ 4gpm, 70% pump efficiency, and take a 20psi difference between operation on relief and off relief as a round number, 0.07hp, or 32 watts.

I'm not following your calcs here. The way I think about it is that it takes 4+ hp at max rpm to drive the oil pump, on a real engine, not some little foreign 4 or 6 popper. Just take 1/3 of that and you have the waste effort. Any of you put a drill on an old cam driven pump? You'll get smoke if you stay on it for more than 10 seconds. I know that's cold oil but its at a really slow speed too.

 

[turtlevette]

Originally Posted By: CATERHAM

If you're routinely thrashing an 6 cyl M series engine then sure maintain the OP 10 or 15 psi higher than spec' minimum which will still of course be below the oil pump relief setting. So you're increasing your self imposed minimum operational viscosity which may still be achievable with a 20 grade oil if the oil temp's remain low such as during cold winter use. Seemingly off topic but actually related, it also pays to maximize the VI of the oil your using because it will lower the OP at low normal operating temp's for a given HTHSV oil rating. This will allow you maximize the HTHSV of the oil used for whatever minimum OP value you want to use.

You've been saying the same thing here for years. Let me see if I can boil it down to a few sentences. 1. Run a thin oil to minimize oil pump bypass. 2. More oil volume circulating is better for the engine. 1. This saves waste energy but may put you closer to design minimum as the engine wears, so you have to constantly look at oil pressure. And it depends. Is it a bottom up oiler? Where are you measuring the pressure? Preferably at the end of the circuit. Too much leakage may leave no flow reserve at the end of the circuit. I don't think its possible to run a thin enough oil to keep the pump totally out of relief. Well, you'd have to run WD-40 maybe. Remember that some designs are very robust, such as an SBC running a HV pump or a big block pump. 2. Maybe and only to a point. Too much oil in the rings leads to a smoking engine especially with a thin oil. Think about this as equivalent to having excessive side clearance on rods with a thicker oil. A large oil volume hitting the bottom of a piston wastes energy too. To me a high quality oil would be better than a higher flow of a thin oil.

 

[camrydriver111]

Legendary thread! It all starts with a simple question.

 

[Shannow]

Originally Posted By: turtlevette

Originally Posted By: Shannow

Only design that I've done that I'm embarrassed about (serves as a good example when mentoring 'though) was a turbine jacking system, where I matched pump flow to system resistance perfectly. Problem was that once the oil thinned at temperature, the internal leakage of the pump increased (thinner oil pumps less in Positive Displacement pumps), I lost flow through the releif/pressure controller, and the system couldn't meet minimum pressure to lift the bearings.

You are fallible. That's a huge f up. That must have cost someone a ton of money. Good engineers always provide a healthy margin in their designs.

Replaced a reciprocating piston pump in a shut down with the same volumetric flow rate gear pump, when the piston pump failed during maintenance...and found out that gear pumps move CONSIDERABLY less thin oil than they do thick. By thick, I mean ISO32 cst worked up until about 70C, when it's viscosity dropped to around 12, and internal leakage reduced the flow that the pump actually moved...upped size from a PN150 to PN180 for less than a grand, getting the machine away, while engineering a more permanent solution for down the track...still an F-up, I agree...LOL, some here posit that a gear pump moves MORE thin oil than thick.

Originally Posted By: turtlevette

Originally Posted By: Shannow

As to power output waste on relief http://www.advancedfluidsystems.com/tools-resources/fluid-power-calculator/ 4gpm, 70% pump efficiency, and take a 20psi difference between operation on relief and off relief as a round number, 0.07hp, or 32 watts.

I'm not following your calcs here. The way I think about it is that it takes 4+ hp at max rpm to drive the oil pump, on a real engine, not some little foreign 4 or 6 popper. Just take 1/3 of that and you have the waste effort.

Assuming that the LS1 isn't a dinky foreign 4 or 6 popper... At 6.8gpm, and guessing that the stocker relief is set at 65psi (10psi per 1,000 RPM, and 6,500 RPM)... Pump drive power is 0.42hp (at a very low 60% efficiency to make the numbers bigger)...put in an extra 10psi of relief valve pressure, and the power rises to 0.49hp...32 watts different...put in the higher volume 10296 pump, with it's 10psi greater relief, and the pump drive power jumps to 0.58hp at 6,500 RPM...another 72 watts over stocker. So if the thin oil, in a stocker, drops the oil pressure by 10psi, there is less heating effect difference than shining a single low beam at the sump...through the relief, which is the point being countered. Realistic revs, on the highway...much less. (Losses in the bearings are another matter)

 

[KrisZ]

I also wonder how much of that pressure drop using a thin oil can be attributed to the oil pump leakage. The pump might be out of relief because it's leaking internally more than on a thicker oil.

 

[OVERKILL]

Originally Posted By: turtlevette

Any of you put a drill on an old cam driven pump? You'll get smoke if you stay on it for more than 10 seconds. I know that's cold oil but its at a really slow speed too.

Many times. Need a good drill with a stock pump. Need a much stronger drill with an HV pump. My cordless wouldn't do it, but a larger chucked old B&D would do it. IIRC, with an SBF, we could get around 10psi on the gauge with the (big, gear reduced) drill maxed, can't remember what we got out of the SBC. An air drill worked a lot better than an electric unit. The SBF was easy to rig up too, due to the hex drive. An extension and a socket taped to it with a 3/8th's adapter on the drill. I remember the first time I did it and wasn't expecting the "hit" of oil pressure, nearly buggered my wrist! LOL!

 

[turtlevette]

Originally Posted By: Shannow

[ some here posit that a gear pump moves MORE thin oil than thick.

Well, the pump moves more oil through the connected network. Right? You're not going to argue with that. That's what they mean. The pump is a little less efficient because of internal leakage, but connected network leakage is much greater. A thinner oil will cavitate at a higher rpm which is a good thing. The hp numbers you're coming up with have to be too low. But I can't prove you wrong calc wise. We're missing something. I'll keep pondering on it. I enjoy busting on you about your design mishap. I've done far worse. I put half a city in the dark for a few minutes testing a diff relay. This is why they don't give screwdrivers to engineers.

 

[Shannow]

Here's an interesting chart, the name of the book is inserted in the picture, and can be found here , and attempt at cutting through the "technical obfuscating nonsense" if you will. Particularly interesting and pertinent, as they chose an engine that they could isolate the number 4 main bearing from the rest of the oiling system, and provide a direct feed, of their chosen viscosity oil, at the temperature that they decided (132C)...and used a constant supply pressure, in this case 60psi. Chart on the left is the time taken for 250ml of oil (at 60psi) to be drawn through the bearing, versus some Newtonian oils, and includes a multigrade with a "KV" value versus it's "apparent", or "bearing" viscosity as some posit. As I have stated previously in the past, the bearings take only what they need...60psi is a fair pressure, and the oil is still not pushed through the bearing. 250ml over a minute or three minutes is tiny...but it's only one of 5 main bearings and 4 big ends....and maybe in a modern design a couple of fixed orifice squirters for piston cooling, chain lubrication, or valvetrain lubrication. The oil pressure is the artifact of the bearings not needing, or drawing all of that flow that the pump can provide...A pump going into relief is not starving the bearings, nor anything else...they just do not need the oil volume pure and simple. Flow does not equal lubrication. As to starving "other" parts of the lubrication system, squirters are typically orifices, and their behaviour is pressure and density related...more pressure equals more flow...hardly starving. Back to the Minimum Oil Film Thickness chart... If load is the same, the bearing diameter and length is the same, the RPM is the same, the only variable change is viscosity...less viscosity is less MOFT...can't have it any other way. Again, using a manufacturer's minimum oil pressure for condemnation of an engine based on parts wear on their recommended viscosity as a tool to find the minimum viscosity that you THINK they meant on a good engine is a fool's errand. Lack of catstrophic failure is not evidence of correct lubrication.

 

[Shannow]

The upper right part of the chart shows what I have been saying forever about the oil pressure not telling you anything about what's taking place on the loaded side of the bearing. The oil feed holes are in the upper side of the bearing, where the clearance is at it's widest...it doesn't give the effect of the 10^6 shear rate until a couple of thousand RPM. You can see that the "apparent viscosity" is being affected by the shear rate, up until the "second newtonian" period at 2,500-3,000 depending on the shear stability of the oil. Problem is that the oil film at the location of MOFT is only microns thick, and is already operating in the high shear regime. So the "apparent" viscosity measured by oil flow rate (or pressure in the engine viscometer case) is not what the bearing MOFT is seeing on the loaded side....it's seeing the high shear viscosity... As we know, lower speed results in even lower MOFT...your oil pressure is telling you nothing about the bearing MOFT behaviour at lower revs.