Ring Gear Rotation and Optimum Temperature Sensor Location

[CarbonSteel]

I have a couple of Metal Cloak axle covers that I will be drilling and tapping for a temperature probe soon. The rear axle I have fully figured out and know where to install the probe for a good temperature reading while the axle is in operation.

Note: these photos are for representation purposes only (these not my axles, though I do have a high pinion in the front and low pinion in the rear as shown).

Taking into account the ring gear rotation direction of the rear axle, the arrow on the bottom photo is typically the path the oil takes from the bottom of the housing and over the top of the ring gear. The temperature sensor is located in the axle cover about where the end of the red arrow ends and the temperature reading is steady while the axle is in motion.

The front axle is where I am scratching my head a little. Part of the problem is there is a front axle disconnect which prevents the ring gear and driveshaft from spinning while in 4x2 mode. I have not been able to get out and into 4x4 mode for any length of time since C19 hit. The few times that I have been in 4x4, the temperature gauge seems to read, but I want to be sure that where I have the sensor located (same place as the rear) is optimum.

My question is this—does the oil in the front axle follow the same path (but in reverse) as the rear axle? In other words, I am assuming the oil goes under the ring gear and under the bottom of the pinion gear, but is there enough that carries over to splash consistently on the upper part of the axle cover?

I searched for a front axle YT video that had a clear cover, but could not find one.

Thanks in advance for any insight.

 

[ABN_CBT_ENGR]

I have a couple of Metal Cloak axle covers that I will be drilling and tapping for a temperature probe soon. The rear axle I have fully figured out and know where to install the probe for a good temperature reading while the axle is in operation.

Thanks in advance for any insight.

I do this all the time for gear systems but the location depends on exactly what data you want and what you want to do with it because there are multiple "correct" locations ( each with a different reading) for a different state of operation.

So, what specifically is your desired outcome or data point for the reading?

 

[CarbonSteel]

I do this all the time for gear systems but the location depends on exactly what data you want and what you want to do with it because there are multiple "correct" locations ( each with a different reading) for a different state of operation.

So, what specifically is your desired outcome or data point for the reading?

ACE - I am just looking to monitor the average temperature of the fluid and not to dive too deep into the various areas of temperature difference (ring gear versus pinion versus bearings). I found a number of clear cover videos of the rear axle and thus my choice for its sensor location. The area is constantly covered in fluid while the axle is turning and is a good spot.

I am less sure for the front since the oil is first directed under the pinion gear. I am trying to keep the sensors fairly high on the cover so that I do not have to work about an off-road obstacle hitting them. The front is the most vulnerable since it is going head on into everything. I may fabricate an skid plate extension to add to the axle cover skid plate to further protect it.

I am just trying to understand if the upper part of the front cover is also bathed in oil as the rear one is.

PS... I have sensors in the OEM covers now and the rear works just fine. I could probably go in 4x4 off-road for about 5 miles and I would know if the front is also in a good spot.

 

[ABN_CBT_ENGR]

Then ideally you want to use a long neck probe and drill/insert is as close to center of where the ring and pinion engage. ( better from the side through the housing rather than the cover despite whats commonly sold)

Here's why you want it there and a long necker ( this comes from Emerson/Rosemount who I partner with for my instrument packages)

You want the average temp of the fluid- that location is where the most energized fluid ( hottest) is that has not started convecting to the inner skin thus artificially lowering the process temperature.

You want the long necker ( as opposed to the stub) because at the point of release by the gear set you will have aerated and densified fluid flow ( just got compressed, heated, mixed with air then jetted out) so it will still be 'releasing" heat- the long neck will average and totalize and give you a more accurate reading over the sump.

That's for the best most accurate online temp

 

[CarbonSteel]

Then ideally you want to use a long neck probe and drill/insert is as close to center of where the ring and pinion engage. ( better from the side through the housing rather than the cover despite whats commonly sold)

Here's why you want it there and a long necker ( this comes from Emerson/Rosemount who I partner with for my instrument packages)

You want the average temp of the fluid- that location is where the most energized fluid ( hottest) is that has not started convecting to the inner skin thus artificially lowering the process temperature.

You want the long necker ( as opposed to the stub) because at the point of release by the gear set you will have aerated and densified fluid flow ( just got compressed, heated, mixed with air then jetted out) so it will still be 'releasing" heat- the long neck will average and totalize and give you a more accurate reading over the sump.

That's for the best most accurate online temp

Unfortunately, that is not practical. I am using ISS Pro gauges and the probe is about 1-1/2" inches long. I also do not want to drill and tap the axle housing so I have to make the best of the cover location.

While the "splash zone" may not be the hottest oil, I have to think there would be minimal temperature loss from the gear mesh area to the sump--especially at highway speeds where the oil is being moved at a high rate.

 

[ABN_CBT_ENGR]

Unfortunately, that is not practical. I am using ISS Pro gauges and the probe is about 1-1/2" inches long. I also do not want to drill and tap the axle housing so I have to make the best of the cover location.

While the "splash zone" may not be the hottest oil, I have to think there would be minimal temperature loss from the gear mesh area to the sump--especially at highway speeds where the oil is being moved at a high rate.

Fair enough. I custom design everything and a kit does limit things a bit so back to the cover.

On the splash zone, you really want to avoid that- here's why

That's aerated oil hitting a probe from one side and direction. That throws the internals ( whether gas, bimetal or direct resistance) out of balance and will eventually render the sending unit out of calibration- possibly damage it. Also, that oil will change velocity on the probe and the overflow on it will wick away some heat making it read lower than it is.( you never want a thermal probe in a splash or stream except in a pipe large enough for forces to equalize.

You will still get close readings but don't take them as the gospel and you should do fine.

 

[CarbonSteel]

Fair enough. I custom design everything and a kit does limit things a bit so back to the cover.

On the splash zone, you really want to avoid that- here's why

That's aerated oil hitting a probe from one side and direction. That throws the internals ( whether gas, bimetal or direct resistance) out of balance and will eventually render the sending unit out of calibration- possibly damage it. Also, that oil will change velocity on the probe and the overflow on it will wick away some heat making it read lower than it is.( you never want a thermal probe in a splash or stream except in a pipe large enough for forces to equalize.

You will still get close readings but don't take them as the gospel and you should do fine.

Yep; I am looking for average fluid temperatures and this should give that to me. Without installing a clear cover that exactly replicates the contour of the metal cover I am not able to know how much oil is hitting the probe from all sides and if I see the temperature trending in a different direction with no apparent reason, I can always replace the probe.

Back to my original question--how can I tell if enough oil will hit the probe area on the front axle since the oil flow is "reversed"?

 

[wpod]

Could you look at some covers that have bungs for a temp probe and just copy the location?

 

[CarbonSteel]

Could you look at some covers that have bungs for a temp probe and just copy the location?

I found plenty for the rear axle, but I have not found any for the front. In the end, I think I am going to have go 4x4 for some miles to see if the location I chose in the OEM covers gives a good reading and thus will work in the Metal Cloak ones.

 

[ABN_CBT_ENGR]

Back to my original question--how can I tell if enough oil will hit the probe area on the front axle since the oil flow is "reversed"?

The only way to know accurately is to build what amounts to a "container" sleeve ( shield, pan, runoff collector, etc.) because for the bimetal to work properly it must have a saturation period.

The problem with these after market kits is that often the people who make them up don't properly engineer them ( in terms of components and application) in the first place so they never deliver the proper information.

Now, on the front you are limited ( by the overall design) as to where it can be reasonably put but just understand what's going on.

In generic systems- the sub sump temp is considered the working process temp and the discharge stream is used to determine if additional loads are encountered by the delta of the two. ( the theory is that additional resistance and load imparts more energy in the form of heat into the fluid)

Then the sump is where the hot fluid stabilizes and convects against the surface area then the properties of the shell convect it against ambient.

Either set up will give you a number but don't make decisions based off of it without other information

 

[Zaedock]

Is this is the same axle from back in May? Gear oil flies everywhere in the diff, thrown by the ring gear and the carrier.

You're going to pick up the heat of the oil, carrier, and air inside the diff. I don't think it will be too far off wherever you place it.

Then the sump is where the hot fluid stabilizes and convects against the surface area then the properties of the shell convect it against ambient.

Either set up will give you a number but don't make decisions based off of it without other information

There really isn't a sump as the oil is constantly churning and thrown everywhere. A 1 1/2" probe in a Jeep axle is definitely going to be hit by hot oil.

 

[CarbonSteel]

Is this is the same axle from back in May? Gear oil flies everywhere in the diff, thrown by the ring gear and the carrier. You're going to pick up the heat of the oil, carrier, and air inside the diff. I don't think it will be too far off wherever you place it.

It is, but the focus is now the front axle. Since the oil flow is "reversed", it goes under the pinion gear instead of over the ring gear and since the probe is in the upper part of the cover, the question was will the oil consistently hit the probe.

To further complicate matters, the ring gear and driveshaft only turn in 4x4 mode since there is a front axle disconnect in the system. I have not been able to find any sources that show typical oil splash patterns on a high pinion front axle. Before I tap and drill the Metal Cloak cover, I want to know for sure. I plan to take it on a extended drive in 4x4 and see if I have consistent readings on the probe that is in the OEM cover now.

 

[Zaedock]

Install it under the fill plug and it will be fine. I've seen many enthusiasts replace the fill plug with a bung as well.

I hope the extended drive is off pavement. Street use in 4x4 will wear the chain in your 241 'case - although you probably know that.

 

[CarbonSteel]

Install it under the fill plug and it will be fine. I've seen many enthusiasts replace the fill plug with a bung as well.

I hope the extended drive is off pavement. Street use in 4x4 will wear the chain in your 241 'case - although you probably know that.

I am trying to keep it high on the cover. If that does not work, then the fill plug would be the next location, but I would have to fabricate an extension on the axle skid plate to protect the probe.

No highway 4x4 will be done; Texas has miles of beach that I can drive to check the function.

 

[ABN_CBT_ENGR]

There really isn't a sump as the oil is constantly churning and thrown everywhere. A 1 1/2" probe in a Jeep axle is definitely going to be hit by hot oil.

That is correct that the oil is constantly worked and thrown but the sump is still there and does have an effect.

This is more in line with the fluid density and specific weight ( which is where you want your sample pulled if you want accurate numbers from the probe)

In relative terms, the sump is where the volume of oil moves least and starts to equalize and totalize ( as opposed to being in various states of working)

Granted this is a true lesser reading than say when the vehicle stops and sits for 5 minutes ( where the temperature would normally climb a few degrees and you see what latent heat is really there)

The OP did specify he wanted the most accurate and that's how to get it. To your point and others, a few degrees off really will make no difference in the grand scheme of things and I agree.

The caution is when people start imagining problems and chasing solutions for them ( and spending money) that it becomes a problem.

 

[Zaedock]

That is correct that the oil is constantly worked and thrown but the sump is still there and does have an effect.

This is more in line with the fluid density and specific weight ( which is where you want your sample pulled if you want accurate numbers from the probe)

In relative terms, the sump is where the volume of oil moves least and starts to equalize and totalize ( as opposed to being in various states of working)

I don't think it would be a few degrees off because the oil is always mixing and the ring gear is only 1/4" +/- from the housing.
A sump is a reservoir of fluid. There isn't enough oil volume to be a "sump"as it is replaced in milliseconds.

A good analogy would be what the temperature of your egg yolk is as you mix it with your fork in a bowl. The entire volume is constantly moving.

Granted this is a true lesser reading than say when the vehicle stops and sits for 5 minutes ( where the temperature would normally climb a few degrees and you see what latent heat is really there)

The OP did specify he wanted the most accurate and that's how to get it. To your point and others, a few degrees off really will make no difference in the grand scheme of things and I agree.

The caution is when people start imagining problems and chasing solutions for them ( and spending money) that it becomes a problem.

Agreed. I think it would be interesting to throw a 10K thermistor strap on sensor on the housing and compare temp readings and also review how the unit/fluid cool over time. Man, we could go nuts thinking about this.

All the while the next guy is out wheeling his Jeep.

 

[ABN_CBT_ENGR]

I don't think it would be a few degrees off because the oil is always mixing and the ring gear is only 1/4" +/- from the housing.
A sump is a reservoir of fluid. There isn't enough oil volume to be a "sump"as it is replaced in milliseconds.

A good analogy would be what the temperature of your egg yolk is as you mix it with your fork in a bowl. The entire volume is constantly moving

Probably not in a pumpkin but I can show dozens where it can be slightly north of 50F different in 2 inches.

The problem is people don't understand instrumentation and thermal transfer. And it does start happening in fractions of a second ( depending on a host of variables and conditions)

The distance of the gear to the housing doesn't mean anything because its not radiating the heat- the fluid is.

That fluid ( fully charged the exact second it leaves the loaded tooth) picks up extreme relative velocity and changes surface area the nanosecond it leaves and starts thinning in terms of dimension.

So it "paints" the probe ( similar to an aerosol)- a bimetal probe cannot react that fast (instrument hysteresis) and is hit with a constant change of the fluid.

So, even in a "churned" ( or churning in real time) sump- even with fluid dropping on top ( forcing old liquid down in relative terms), you will see an element of normalization where fluids self totalize.

Granted that's still not fully accurate but we cant account for the insulation quality of the housing which will hold the latent heat while it is convecting to atmosphere).

That's a short version of thermal properties of a fluid.

But we don't need absolute or laboratory accuracy for the average off-road vehicle but when people want to compare numbers, they need to be aware that the numbers they see on that gauge are significantly different than what the true numbers really are.

That's all, I was just making a point of awareness.

 

[Zaedock]

Yeah I hear you. I do building automation for a living and work with RTD's and thermocouples often.

In regard to the distance of the ring gear to the housing, I was referring to the lack of space for a sump to exist. I agree that temp measurements can vary greatly. In an ideal world, an averaging probe would be better suited if it would fit and was practical.

Good discussion here though. - On an axle that will likely be used <5% of the vehicle life, unless he wheels often.

 

[CarbonSteel]

Yeah I hear you. I do building automation for a living and work with RTD's and thermocouples often.

In regard to the distance of the ring gear to the housing, I was referring to the lack of space for a sump to exist. I agree that temp measurements can vary greatly. In an ideal world, an averaging probe would be better suited if it would fit and was practical.

Good discussion here though. - On an axle that will likely be used

Lots of time in WY/CO/MT so it will see quite a bit of 4x4 action as have my previous 4x4's--C19 put a damper on it for 2020 or I would have already been out there. While the axle type I have (a D44 ELD) has not had any issues, Jeep has a in the D44 LSD axles with many of them failing before 20K. For me, the low capacity of the axles and that I already had the gauges is why I am pursuing installing them permanently into my Rubicon.

The rear axle hits 205°F on the open road and is a data point that I would not have had if I had not installed the temperature gauges.

 

[ABN_CBT_ENGR]

Yeah I hear you. I do building automation for a living and work with RTD's and thermocouples often.

In regard to the distance of the ring gear to the housing, I was referring to the lack of space for a sump to exist. I agree that temp measurements can vary greatly. In an ideal world, an averaging probe would be better suited if it would fit and was practical.

Good discussion here though. - On an axle that will likely be used

Ahh, a kindred spirit.

The whole thing is ( like my comments about UOA)

Any temp that the bearings and gears can withstand ( and the seals) is acceptable provided the lubricant is within that tolerance.

Since automotive gearing isn't always manufactured true to AGMA, you cant always use those standards.