TheSamba.com :: View topic

Sat Jan 12, 2013 10:28 am

Wildthings wrote: nemobuscaptain wrote: Wildthings wrote: VW recommended 15w40 for any temperature that they recommended 20w50 for. Modernize a bit and go to a synthetic oil and anything between 0w40 and 15w40 should be just fine for a WBXer engine. Sufficient oil pressure is great, more than sufficient just causes the pump to do more work and creates heat that must be dumped.

Since the viscosity of a synthetic (or even a dino oil) with a wide spread changes less with temperature, you might even have higher oil pressure with a 0w40 synthetic at say 240° than you would with a 20w50 oil while being less apt to send the engine into relief at lower engine temperatures.

Most WBXer engines seem to die from either water leaks or rod bolt stretch, it doesn't appear to me that wear is really that much of a problem.

I notice that despite your near religious devotion to oils that aren't listed on the VW application charts, you never post anything written from any authority (ie the factory) that supports your propositions.

You seem to think that any oil that has "40" as the top number is good enough, yet that simply isn't the case. If that were the case, VW (and pretty much every other manufacturer) wouldn't list different operating temps ranges for 5w30 and 10w30.

You just don't have a clue about oil viscosity and what the numbers mean.

Maybe my eyes have just gotten bad, but it looks to me likke VW listed 15w40 in their application charts. My authority is VW as per the '85 owners manual, have you ever looked at yours?

I think you will find that VW didn't change their viscosity recommendations much over the Vanagon years, in fact they have been recommending either 15w40 or 20w40 at all temps they have recommended 20w50 for since the mid '70s. As for 5w30 and 10w30 I have stated that I used to run those oils when I used to make seasonal oil changes before switching to synthetics 15 years ago. No problems with running them today if you can find one that hasn't had the ZDDP levels reduced. Note that oils with a second number greater the 30 are not required to run reduced ZDDP and whence one of the reason I run and recommend an oil with a second number of 40, while most --w30 are going to have reduced ZDDP.

if this manual is your authority, why is 0W-40 not listed as acceptable? maybe it is invisable, just like wear in the wasserboxer is invisable?

Sat Jan 12, 2013 10:37 am

If you really, really want a thick oil use this German Castrol 10w60 synthetic as BMW recommends for the "M" engines.

At $15 a liter it is a waste. The valve train in a WBX engine is not very stressed unless you installed a high lift camshaft and very stiff valve springs. The 50w or 60w are overkill for a stock WBX engine application.

Some of the "M" BMW engines had rod bearing problems which is why BMW went to a 10w60. That was a patch solution..some engine bearings still failed.

If you think you must have a high oil pressure reading when driving and want some cold start-up protection, this is your oil.

If you want to keep engine wear down..your piston ring packs clean use a good synthetic engine oil. Your WBX will live for many miles. a good xxw40 is fine.

Sat Jan 12, 2013 9:00 pm

if this manual is your authority, why is 0W-40 not listed as acceptable? maybe it is invisable, just like wear in the wasserboxer is invisable?

No 0w40 or 5w40 synthetic engine oils were commercially available till long after Vanagons were out of production.

Mobil1 had been around since 1976 but not accepted as a generally approved engine lubricant in the automotive industry till around 1995. Mobil1 (and others) did not offer a Xw40 till much later than that.

Mon Jan 14, 2013 2:25 pm

Two comments:

1. With regard to oil pressure bypass in the filter, remember that your oil pressure is created by the oil pump and resistance to flow ahead of the oil filter, not behind. Therefore at cold start, the resistance to flow created by the bearing clearances, oil squirters etc. is after your filter, not before it. Given that situation, it is pretty unlikely you'd be seeing the bypass on the filter opening as the pressure differential across the filter is likely small as flow rates on cold oil are much lower (as evidenced by high cold oil pressure) Not sure if the tests cited (oil flow/temp vs oil filter differential) used a live engine?

2. 0w-40 is just fine, as long as you're not running a van at 80+ temps under heavy load. If you stick to 5w50 you're covered in all situations.

Regardless, oil viscosity choice should be dictated by your oil pressure. If you're seeing ~ 2 bar at 2000rpm, under the heaviest heat/work loading your van will see during the oil change interval, then whatever you're using in the crank is fine. Running the van in both -20C and +35C, and only doing 1 oil change/year, I leave 5w50 in there based on what I'm seeing on the gauges.

Mon Jan 14, 2013 6:32 pm

denwood wrote: Two comments:

1. With regard to oil pressure bypass in the filter, remember that your oil pressure is created by the oil pump and resistance to flow ahead of the oil filter, not behind. Therefore at cold start, the resistance to flow created by the bearing clearances, oil squirters etc. is after your filter, not before it. Given that situation, it is pretty unlikely you'd be seeing the bypass on the filter opening as the pressure differential across the filter is likely small as flow rates on cold oil are much lower (as evidenced by high cold oil pressure) Not sure if the tests cited (oil flow/temp vs oil filter differential) used a live engine? Having the filter go into bypass really doesn't hurt much, if you remember Type 1 engines filter their oil at all and lasted long enough.

The flow rate is determined by the pump volume and the engine rpm, and the flow rate determines the pressure drop across the filter and thus when the bypass open. The actual pressure against the pump has a relatively minor effect on the pump flow rate and thus little effect on when the bypass opens. The filter is most apt to go into bypass when the viscosity and rpm are both high, pretty much right after a start on a cold winter morning when you are first revving the engine to pull out into traffic.

I agree that one oil can be run year around. The first/lower number determines how easy the engine will crank on a winter's day, and the second number the oil pressure at 212°F. A 5w-- will cover most of the northern tier of the US during the winter months and 10w--, 15w--, or 20w-- oils as you go further south. I have been running primarily 5w40 synthetics year around for years at this point in all my engines. They typically go a year or more before I change them out, for my truck which sees low miles this may mean the same oil stays in the crankcase for 2 or 3 years. On my Bay which runs 12-15,000 miles a year and most years has gotten just one oil change I figure the quart of makeup oil it gets every 1500 miles is quite sufficient to keep the additive packages in prime shape. But as I am now wintering in the arid SW and seeing way more dust the Bay will now be seeing at least two oil changes a year.

Tue Jan 15, 2013 9:19 pm

Agree 100% on the oil thing, however a few observations on your comment: Quote: The actual pressure against the pump has a relatively minor effect on the pump flow rate

The oil pump spec and bypass valve setting is a fixed number dictated by mechanics..so once installed is not a variable, assuming normal wear. The resistance to oil flow however is dictated primarily by the bearing clearances, filtration, piston squirter specs, etc. if the pump just spilled out into a bucket you would see great flow but near zero pressure at the pump exit.

If flow (GPM) is described as below, then the working variables that we can easily adjust would boil down to temp, and oil viscosity. Pump volume specs increase with rpm, which is logical.

Oil flow=3.5 GPM @ 2000 RPM @ 30 PSI using 5W-50 oil @ 212 F

Increase bearing clearance and pressure drops, flow increases.
Increase oil temperature and viscosity drops, pressure drops, flow increases.
Decrease oil viscosity and pressure drops, flow increases.

Given the cold oil pressures we tend to observe (high), a 0wXX oil is always going to be best for max flow at cold start. So assuming the oil pump and internal engine bits are within spec, the only thing left to worry about is the max engine oil temp (add an external cooler/thermostat) and the XX in the 0wXX. Without an engine oil pressure gauge, you can't be sure if 0w40 or 0w50 is best. 0w50 is not stocked anywhere here, so 5w50 was the only choice. I just fired up the van at -15C with 5w50 (it's not on the road during winter) so I could use the man cave tonight. Fired right up instantly after sitting for 2 months :-). Since sorting out injector vacuum leaks and setting up the Digifant properly the van seems to start/idle at all temps flawlessly...finally.

Tue Jan 15, 2013 11:20 pm

denwood wrote: if the pump just spilled out into a bucket you would see great flow but near zero pressure at the pump exit.

If the pump just spilled into a bucket the flow would be only slightly greater than if it first had to pass through an orifice that caused 80 PSI of back pressure on the pump. The oil pump is a constant displacement pump there is no variability to it's output except as caused by rpm and internal leakage. If you block off the outlet of the pump the pressure will go through the roof as the pump tries to pump its normal volume, but since it can not do this something will have to fail, typically the drive key.

The relief in the filter only responds to the pressure differential across the filter which is much lower than the pump outlet pressure. For a Fram PH-8a filter the bypass should open when the pressure differential exceeds 12 psi, most other filters have similar bypass pressures.

http://www.framcatalog.com/PartDetail.aspx?b=F&pn=PH8A

Quote: If flow (GPM) is described as below, then the working variables that we can easily adjust would boil down to temp, and oil viscosity. Pump volume specs increase with rpm, which is logical.

Oil flow=3.5 GPM @ 2000 RPM @ 30 PSI using 5W-50 oil @ 212 F

Increase bearing clearance and pressure drops, flow increases.
Increase oil temperature and viscosity drops, pressure drops, flow increases.
Decrease oil viscosity and pressure drops, flow increases.

Given the cold oil pressures we tend to observe (high), a 0wXX oil is always going to be best for max flow at cold start.

The pump flow at cold start is going to be the same for a thick oil as a thin oil right down the to the minimum cold pumping temperature, which for a 20wt oil is 0°F and for 0wt oil -40°F. The pump is constant displacement and it not much at all effected by temperature so long as the temperature is above the minimum cold pumping temperature. Yes the regulating/relief valve may dump oil but the oil pump is still going to be pumping the same volume for the same rpm.

Wed Jan 16, 2013 9:28 am

Look at this technical data for BSM rotary gear pumps: http://www.bsmpump.com/pdf/Section14_Engineering_Data.pdf

The friction loss multiplier used in their GPM formula can vary from .3 at 32ssu (reading off 5GPM section) to 2.7 at 500 ssu.

So to determine flow, BSM at least is very much concerned with oil viscosity and operating temperature in spec'ing a hydraulic rotary gear pump :-)

I'd say that your previous post would be true if the gear pump was 100% efficient.

Wed Jan 16, 2013 11:00 am

denwood wrote: Look at this technical data for BSM rotary gear pumps: http://www.bsmpump.com/pdf/Section14_Engineering_Data.pdf

The friction loss multiplier used in their GPM formula can vary from .3 at 32ssu (reading off 5GPM section) to 2.7 at 500 ssu.

So to determine flow, BSM at least is very much concerned with oil viscosity and operating temperature in spec'ing a hydraulic rotary gear pump :-)

I'd say that your previous post would be true if the gear pump was 100% efficient.

What is "ssu"?

Wed Jan 16, 2013 2:39 pm

Not sure why BSM chose SSU...however that was their choice in the tech data. From:

http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html

Quote:
Other Commonly used Viscosity Units
Saybolt Universal Seconds (or SUS, SSU)

Saybolt Universal Seconds (or SUS) is used to measure viscosity. The efflux time is Saybolt Universal Seconds (SUS) required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer, under carefully controlled temperature and as prescribed by test method ASTM D 88. This method has largely been replaced by the kinematic viscosity method. Saybolt Universal Seconds is also called the SSU number (Seconds Saybolt Universal) or SSF number (Saybolt Seconds Furol).

Kinematic viscosity versus dynamic or absolute viscosity can be expressed as

ν = 4.63 μ / SG (3)

where

ν = kinematic vicosity (SSU)

μ = dynamic or absolute viscosity (cP)

SG = Specific Gravity

Wed Jan 16, 2013 3:24 pm

denwood wrote: Not sure why BSM chose SSU...however that was their choice in the tech data. From:

http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html

Quote:
Other Commonly used Viscosity Units
Saybolt Universal Seconds (or SUS, SSU)

Saybolt Universal Seconds (or SUS) is used to measure viscosity. The efflux time is Saybolt Universal Seconds (SUS) required for 60 milliliters of a petroleum product to flow through the calibrated orifice of a Saybolt Universal viscometer, under carefully controlled temperature and as prescribed by test method ASTM D 88. This method has largely been replaced by the kinematic viscosity method. Saybolt Universal Seconds is also called the SSU number (Seconds Saybolt Universal) or SSF number (Saybolt Seconds Furol).

Kinematic viscosity versus dynamic or absolute viscosity can be expressed as

ν = 4.63 μ / SG (3)

where

ν = kinematic vicosity (SSU)

μ = dynamic or absolute viscosity (cP)

SG = Specific Gravity

ah, that expalins it, thanks! I am used to Centistokes as a unit of viscosity. by the way viscosity is oft measured by a machine that spins a rod or cylinder in the liquid to be tested, the resistance to the spin is indicated on the machine. Different diameter rods or cylinders on the rod are used for different reading ranges.

Thu Jan 17, 2013 4:20 am

denwood wrote: Look at this technical data for BSM rotary gear pumps: http://www.bsmpump.com/pdf/Section14_Engineering_Data.pdf

The friction loss multiplier used in their GPM formula can vary from .3 at 32ssu (reading off 5GPM section) to 2.7 at 500 ssu.

So to determine flow, BSM at least is very much concerned with oil viscosity and operating temperature in spec'ing a hydraulic rotary gear pump :-)

I'd say that your previous post would be true if the gear pump was 100% efficient.

Your link doesn't seem to work so I can open in an see what it says, but it probably supports my statement

Quote: The oil pump is a constant displacement pump there is no variability to it's output except as caused by rpm and internal leakage.

If you dead head your pump and try and get it to put out 2000 psi then yes you are going to have high losses in the moment before the drive key shears, but under normal operating conditions the flow losses are going to be fairly minimal, and as far as the opening pressure of the bypass valve in the filter is concerned will not cause the effects you state. The bypass valve operates off of the pressure differential across the filter and doesn't much care what the back pressure is in the system. The same flow that allows the bearings to create back pressure is also going to cause a pressure drop across the filter, that is just the way it is.

Thu Jan 17, 2013 9:33 am

Of course output must be defined, as flow rate is an output as is pressure an output of a pump.

In a constant volume pump, pressure can vary a good deal at a given rpm based on viscosity (which has a temperature variable component)

most pumps are not ideal, some can have more internal leakage than others, ( this can vary with viscosity/temperature).

A worn pump may be have a lesser flow rate when given a large back pressure than with no back pressure, because of internal leakage. The more worn the pump, the more this effect comes into play. The thinner the oil, the more leakage will occur in a worn pump, thus reducing valume and pressure output. the more worn the pump, the greater the effect.

Mon Jan 21, 2013 2:35 pm

Wt, the friction loss mulitipler does not support your argument. We have BSM using the friction loss multiplier, as a function of viscosity to calculate GPM, as linked : http://www.bsmpump.com/pdf/Section14_Engineering_Data.pdf (so they use a friction loss multipler in their calculation).

Alternatively, these folks offer up a few curves to calculate GPM on a gear pump: http://www.pumpscout.com/articles-expert-advice/gear-pump-sizing-tips-and-advice-aid245.html

Note the image (Curve 3) below which at 75psi and SSU of ~380 has a GPM slip value (loss) of 1 GPM, however take this viscosity to 30 SSU and you have a slip value of 6.5 GPM. This clearly indicates that given a rotary gear pump, GPM changes with viscosity..and indeed for a stationary pump, you must increase RPM as appropriate to compensate. So in the situation where a cold engine and oil are warmed up from 32F to 190F, the chart below could be used to approximate the difference in oil flow (GPM). For reference, a few SSU values as well:

SAE 10 -> at 150F=150 SSU vs 210F=43 SSU
SAE 20 -> at 150F=330 SSU vs 210F=51 SSU

Mon Jan 21, 2013 6:39 pm

I don't see where Graph #3 proves me wrong at all. First off it doesn't say what the displacement of the pump is or the rpm. That graph doesn't say or even imply that the slip lossages are more than a few percentage points at most. Pretty trivial in my opinion. It certainly doesn't prove your incredibly erroneous assertion that there is no pressure differential across the filter when the oil is cold because there is so little flow. If anything it shows just the opposite, that the flow is still quite high. When the oil is cold there is very little slippage at all so there is a full flow of oil trying to force its way past the filter and then because the pressure is still so high much of the energy spend pumping a viscous fluid is just going to be lost as the oil spills through the relief.

His statement just above chart #5 implies that during the worst conditions the pump will likely work with an efficiency of just around 50%, but this is almost all pumping losses due to stirring around a viscous fluid and not losses due to slippage. The pump output volume when the oil is cold and viscous is still high as there is little slipage

Quote:
Notice that with the last two curves, if you are running your gear pump at higher speed and viscosities, the viscous horsepower can equal or exceed the input horsepower.

Mon Jan 21, 2013 7:58 pm

Of course there is pressure differential across the filter...no disagreement there. Read the rest of the data on the curves, rpm chart is provided..I'm only linking one of them to avoid copying in the entire doc. My point is simply to provide several technical references on gear pumps which demonstrate that a rotary gear pump output is not constant. GPM varies at a given rpm based on viscosity (or temp) and the pressure it's running at. The pump is not 100% efficient (slip) increases with pressure and decreased viscosity. Therefore a cold engine is flowing less oil than when it is warm. Pretty hard to argue this unless you ignore the technical pump data I've linked.

Further, the oil pump with oil at 0C has likely nearly zero slip (loss), and resistance to flow is also very high aft of the filter (based on the data from BSM, friction loss multiplier at high SSU)...so pressure at idle easily exceeds 75psi, and the bypass is required. This speaks to the importance of correct weight oil for cold weather starts...making a very good argument for 0w40 or 0w50 oil in the van.

In any case, hope at least someone else finds the thread interesting :-). To plagiarize Forrest Gump, "That's all I've got to say about that.."

Cheers,
Dennis.

Wed Jan 23, 2013 1:33 pm

I had to add it:

So, as you can see a 5W20 doesn't have the same visco as 5W40 when cold.
So, saying a 5W50 will fit all isn't really accurate. It isn't going to destroy the motor in a short time but doesn't really do the job up North.
I really prefer to use a 5W20 during the winter for cold start as at 40C, a 5W40 is twice thicker as a 5W20. I don't even want to imagine what is the diference under 0C....

Wed Jan 23, 2013 6:41 pm

Ok, so you piqued my interest there :-) That chart is interesting. Not seeing it before I would have assumed cold that 5w is 5w. I have noticed the pour point thing with synthetic in my garage at cold temps given dino vs synthetic of the same grade...and certainly the synth guys market this fact. I would guess the oil in the chart you posted is not synthetic? Just a random google search and some amsoil data.

So big difference even across the same grade Dino?? vs synth 10w30 tested at -25C. If you compare the 10w30 in your chart at 12000@-30C vs amsoil 3500@-25, there is a huge difference.

5w20 makes complete sense for cold start but once the oil is at 100C, hot oil pressure (at least in my setup) would be a real issue. Would be very interested to see the chart you posted, but with a synthetic tested..

This article is a good read:
http://www.carcraft.com/techarticles/synthetic_vs_conventional_oil/
Suggests the 10psi drop in oil pressure testing 20w50 vs synth 0w30 may be just fine. They picked up ~2.5% in terms of HP as well.

Incidentally, fired up the van and left it outside the unheated garage at -27C last night to free up some workspace. Fired up first crank (with 5w50 synth in there) this am to be put back to bed. I didn't plug in the block heater intentionally to see if would start. Can't say the same for the power steering which was stiff like crazy at those temps. 2 nights ago, -37C plus wind chill...-45C. No one without block heaters was moving anywhere..

Wed Jan 23, 2013 9:33 pm

denwood wrote: Of course there is pressure differential across the filter...no disagreement there. Read the rest of the data on the curves, rpm chart is provided..I'm only linking one of them to avoid copying in the entire doc. My point is simply to provide several technical references on gear pumps which demonstrate that a rotary gear pump output is not constant. GPM varies at a given rpm based on viscosity (or temp) and the pressure it's running at. The pump is not 100% efficient (slip) increases with pressure and decreased viscosity. Therefore a cold engine is flowing less oil than when it is warm. Pretty hard to argue this unless you ignore the technical pump data I've linked.

Further, the oil pump with oil at 0C has likely nearly zero slip (loss), and resistance to flow is also very high aft of the filter (based on the data from BSM, friction loss multiplier at high SSU)...so pressure at idle easily exceeds 75psi, and the bypass is required. This speaks to the importance of correct weight oil for cold weather starts...making a very good argument for 0w40 or 0w50 oil in the van.

In any case, hope at least someone else finds the thread interesting :-). To plagiarize Forrest Gump, "That's all I've got to say about that.."

Cheers,
Dennis.

You seem to have gone to a lot of effort to disprove you own post.

denwood wrote: it is pretty unlikely you'd be seeing the bypass on the filter opening as the pressure differential across the filter is likely small as flow rates on cold oil are much lower

Thu Jan 24, 2013 7:52 am

bluefirefly wrote:

So, as you can see a 5W20 doesn't have the same visco as 5W40 when cold.
So, saying a 5W50 will fit all isn't really accurate. It isn't going to destroy the motor in a short time but doesn't really do the job up North.
I really prefer to use a 5W20 during the winter for cold start as at 40C, a 5W40 is twice thicker as a 5W20. I don't even want to imagine what is the diference under 0C....

The reason that you are seeing such a difference in viscosity between various 5w-xx oils at 40°C is that 40° is way above the temperature a 5w-xx oil is rated at. The viscosity of a 5w-xx oil is supposed to be around 3500cP at -25°C. See the blue chart in this link:

http://www.upmpg.com/tech_articles/motoroil_viscosity/