For anyone who really wants to know how this works in order to diagnose or improve a system or even make a decision on "if" or "what" to buy regarding this subject- the actual facts and proper methods need to be presented to show what is and is not realistic or even possible. Then address the claims and see how they measure up against proven and accurate industrial technologies and techniques
Put this in conversational English and light on technobabble for ease of reading and understanding without a copy of Mark's handy. (so some technical accuracy may be sacrificed)
The claim made (as based on the Banks video) is basically this particular cover is "best" because it
Controls Foaming
Lubricant Aeration
Reduce Temps
Improve Mileage
"Look Biochin"- can't really define this in terms of established engineering standards so will have to skip it and leave it open to the interpretation of the buyer. ( looks nice to me personally)
Got have some background (table of standards) for the evaluation baseline and these are easily reviewed in Marks, Gear design manuals, books on tribology and are industry standards.
This is the basic premise how any industrial gear system would be done to verify the claims on a part. It would have to be highly controlled or the results would not be able to be validated in any meaningful way.
Going to put aeration and foaming together since they are in the same family.
Air gets into oil in basically 4 ways.
Free Air - Entrained unbonded atmosphere that is mixed in the oil and tries to get to the surface depending on the viscosity etc. (aeration) This comes in gears basically from pockets of air getting trapped as the tooth breaks the surface. (not unlike a paddle wheel) Other sources can come from sloshing, air entering, vortexing and all kinds of things. Basically, it's a mechanical capture. (Also, in hydraulics and other closed systems, "free air" is like a bubble or pocket trapped in the system that can cause spongy actions and "entrained air" is in the oil but in sumps- free air is generally the atmospheric air that's inside the sump with the oil- it doesn't get "entrained" until worked- just to avoid any confusion)
Cavitation- This comes from low pressure vapor shear (no different than in a pump or propeller) so its air "from" the oil as opposed to external air trapped in it. Cavitation seldom breaks the surface and is usually absorbed back into the fluid unless excessive volume is produced.
Dissolved Air- It's a form of precipitation where the air chemically breaks down and bonds with the oil molecules. Almost invisible in most cases but in vanillas can appear "cloudy" or waxy. This is a natural occurrence usually to a point but various things like pressure, depletion and other reactions can greatly enhance it. This one really goes beyond the available data in the video or advertising claims and requires detailed analysis to comment on further so its just mentioned as a reference.
Foam- Foam is basically "air" on top of oil that has a meniscus and gets thinner as it comes up until it pops based on dispersants, surface tension etc. qualities of a given oil. Foam is only a mechanical problem if and when it gets sucked into the parts because then you are lubricating with literally nothing but air. In most cases aeration leads to foaming proportionally.
The typical differential gear is a helical spiral bevel class gear. This is significant in gearing because unlike spurs and some volute gears that literally "hit" at the pitch line and slide- the "helical" design is more like a worm (for visualization) that has a leading contact moving to a true load zone with a trailing edge so it transfers power along a gradient.
Therefore, when you set them you have a contact patch usually slightly off center toward the leading edge in terms of feed and rotation. This type of mechanical "wipe" creates more cavitation induced action due to the "slide" than a typical spur or helical straight gear.
However, this specific design, since it "squeezes" oil along the contact patch generates a "degree" of EHD lubrication along with the boundary lubrication. (said degree varies greatly with contact profile, tooth dimension and other factors from virtually none to it becomes a significant damper and lubricator) This is why some surface spalling is considered normal in this type of gearing and its still considered a boundary lubrication regime by classification.
Since it "squeezes" the oil, it does increase exit velocity (Bernoulli and Poisson) and spraying it against a wall will aid in dispersal ( a critical part of the cooling process) but that process doesn't "generate" or entrain air itself although when observed visually can give the "illusion" of said effect except in the most extreme of cases like in a centrifugal pump at high RPM)
This short blurb establishes that aeration from both entrained air and cavitation (percentages not assigned) is a direct result of the proper design and operation of this class of gear. Degrees of both are directly related to RPM, load (defined as tooth deflection and distortion relative to the load) lubricant selection, cooling, stabilization (how long fluid can relax before being worked again) and a few other factors.
The presence and effects are properly measured by vibration analysis in terms of gear frequencies with RPM and tooth count and bearings with type and ball count. If desired a reference scratch can be put on a specific tooth and the gears can be referenced through a hunting tooth frequency for pinpoint accuracy.
The set up would be similar to the following to control all external variables to specific performance parameters to a specific cause.
For loading changes, the brake motor (dyno in this case to add measured resistance) would be attached to the output shaft/PTO (in this case the tires removed to eliminate any tramp inputs) and a direct couple put to the input shaft (in this case driving the differential directly and no other drive components) Overall backlash would also be measured so it can be accounted for as thermal growth to duty dimensions is recorded. (that's a critical thing)
Cooling would be pretty much a fan as simulated in the video. (cfm at simulated velocity at ambient conditions is pretty much the standard)
Variations in load, lubrication, mechanical looseness, spin etc. will be identified and measured with greater than 99% accuracy. This is the standard and well recognized gold standard on how this is done. Other techniques such as ultrasound and thermography can be used but with lesser accuracy in the critical measurements in terms of frequency and time domain analysis for the items in question.
That's a basic set up to assess a gear train in the areas mentioned.
To measure impact of the item on the fluid- you would have to have in service working samples taken and analyzed in real time visually and with other tests depending on the information desired- since this was not done nor part of any claim it will just be mentioned but not pursued.
Cooling- To measure cooling, there would have to be contact probes installed at the point of excitation (as close to the engagement line as practical on the gears) then in the sump right at it, and the farthest end. This is to establish how much energy is being put into the fluid (and by volume relative to load/rpm) to serve as the baseline.
Then there must be both contact probes and thermal imaging along the entire radiant surface of the conducting housing. (the entire housing is a heat transfer device; the cover is only a small part)
The design of these housings is where the front edge starts the transfer so dead air at the end in the dead zone (the back side) is a secondary cooling area.
The only way to legitimately determine the % contribution of the claimed cover will be to know and measure all the heat as indicated and then remove the contributions of other elements. Whatever is left is the direct contribution of the cover and its design.
In short, with nothing but industry standards proven to deliver accurate results and the claims in the video- the following claims made can be realistically validated with a high degree of legitimate accuracy.
Controls foaming and aeration:
No proper testing was performed to address this claim in any manner so any claims along this line are not supported by anything. Logically a rear cover (inspection port in any other type of gearbox) would play little to no part in either because it has nothing to do with the generation of the aeration at the gearing where it happens and equally as little with the removal.
It could be argued that some of the dimpling and internal finning "could" create a dead zone allowing fluid to relax and release some entrained air but given the overall volume and internal area of a typical pumpkin type differential, this amount would be statistically insignificant.
Reducing Temps:
This design clearly increases surface area and creates a unique air flow which will enhance thermal transfer. Of that there is no question. The degree of cooling and percentage of contribution cannot be accurately measured, differentiated claimed by the tests demonstrated in the video.
Improve Mileage:
Nothing in the tests as performed in the video can legitimately claim any contribution related to any savings, improvement or other change in mileage SPECIFICALLY AS A RESULT OF ADDITION OF THE DIFFERENTIAL COVER ONLY. Too many uncontrolled variables included combined with "data" not directly linked to mileage which cannot be separated and assigned to the cover specifically.
So, the cover will contribute to fluid cooling (even in static air as it would rise over the fins removing some heat) to an unknown degree that would be situation specific. Beyond that is just typical marketing hyperbole not much different than the average infomercial.
