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"Rear Axle Differential Temp Increased, Decrease Speed" warning

Brent Dalton

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I wanted to consolidate this information as it's floating in a few different places currently and I believe this issue will show it's ugly head to more owners in the future.

On the 3rd day of an HPDE back in February at Circuit of the Americas, I heard a ding and I looked down and saw a "rear axle differential temp increased, reduce speed" or something close to that. It was roughly 80 degrees outside. I had just ran a full 30 minute session, took a 30 minute break, and then went back out and was about 15 minutes in when I got the warning. My car was also on 295 Hoosier R7's. I was also on stock ford fluid.

So my first question was:

What temperature does this message trigger at? I was hoping that it came on earlier rather than later. The answer thanks to a forum member and mechanical engineer at Ford : 293 degrees Fahrenheit.

As soon as I the message popped up, I backed off and drove around outside the track to cool everything down. I changed the fluid to amsoil since. I did drive the car 12 hours home, ran an AutoX, and daily driven the car for several weeks now as I've had other stuff to do that has taken me away from finishing up the work on my actual daily driver. There is no noise and everything appears to be in order. Maybe I reduced the life of the diff. Who knows.

So the 2016 mustangs have a diff temp sensor. The 2015 Mustangs DO NOT have the diff sensor. I have been unable to find a way to tap into the computer to be able to monitor the diff temp. Obviously it is not something you can monitor through the dash. I tried an OBD II reader with the torque app and did not have any luck. I'm trying not to void my warranty so I have not hooked up vcm suite from hptuners on it. Has anyone been able to pull up the differential temp via an ngauge or some other source? Does anyone know if it shows up in hptuners?

So I think mitigation:

-better fluid
-a way to monitor the diff temp
-diff cover with increased fluid capacity. Non exist currently, but I think there might be a market for this.
-if the diff cover with increased fluid capacity doesn't work, the next step would be an external diff cooler.

Would love to hear thoughts/feedback/etc... from the other track guys or anyone who has also experienced this.
 

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On my 15 Ecoboost I would use a infrared gun and it was "hot" well over 220+

I'm thinking that these high temps is what made my rear end noise get really bad over time.

My plan was to have a billet finned diff cover made with provisions for a diff cooler.

If anyone is interested in this I could make something happen but it won't be cheap.

600-1000 would be the range.
 

Brent Dalton

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I'm also looking into a cast diff cover with an extra quart or two capacity with the ports for the diff cooler. It's what I run on my rx7. Just doing the initial brainstorming right now. Like you said, it won't be cheap.
 

OppositeLock

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Has anyone tried an aftermarket diff cooler? Or maybe a gt350 TP one? Luckily never run into a problem at an autox, but generally theres a bit of cooling time between runs.
 

Brent Dalton

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Great point. So that's what the mech engineer at ford just brought up(GT350 set up). He said it's a slick set up, but thinks it would be hard to source the pump and diffuser possibly. I just asked if he knew if it was a bolt on solution. Waiting to hear back, but if anyone knows, please post up.
 
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It would bolt up pretty easily.

You'd want to get the gt350 rear diffuser for sure. Next step would be wiring.

I think the most cost effective solution would be to get a mocal pump, get npt to 10an adapters. Then get a 5 row cooler and mount it behind the swaybar.

I'd wire it to a switch for sure.

On the gt350 it shows axle temp under afrs, the red zone is 300f or higher.
 

Gatorac

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Gaining IRS meant we lost all the additional metal around the rear diff to absorb the heat. Putting together a diff cooler shouldn't be to hard. I would steer away from the Mocal/Tilton fluid pumps. I've used those before. Noisy and not the most reliable. Another member came across this pump. http://www.rbracing-rsr.com/oilsystems.htm Looks like a lot of thought went into it. It shouldn't be affected by the high temp of the fluid like the Mocal one can be. Haven't really looked for mounting locations yet but it's a big car so there should be a suitable place for pump and cooler. The spare tire well might work as a last resort. Keeps everything nice and safe from flying debris.
 

jpilone

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I got this as well. I attributed this to my magnaflow exhaust routed directly under that sensor. I have exhaust wrap for it now that I will install before my next track day, and will change the fluid to royal purple too.
 

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jpilone

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yeah, mine are fairly close to that little sensor (which is at the very bottom of the diff case, close to the exhaust! duhh!).

Thanks on the congrats. I can't wait for it... hopefully by xmas
 

Optimum Performance

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P188A Differential Oil Temperature Too High / Too Low:

This DTC sets in continuous memory when the differential oil temperature exceeds 145° C (293° F).

Brent, I don't know if you scanned your car after the warning came up but I am looking everywhere in the service manual but nothing is mentioned for the Diff Temp other than Shelby Temp Warning. Maybe it is the same but they do not appear to have a gauge for it like we do for EOT in the GT. I'm not sure what threshold voltage is used for turning the GT350 cooler pump on. If your Ford friend could enlighten us we would appreciate it.

Normal Operation and Fault Conditions

"When the differential oil temperature reaches a predetermined level, the PCM grounds the differential oil pump relay which activates the differential oil pump. Once the oil temperature is reduced to another predetermined level, the PCM stops grounding the relay. While the relay is activated, the PCM continues to monitor the differential oil temperature and expects to see a reduction in the temperature. If the PCM does not see a reduction in the temperature or if the temperature continues to rise, a DTC is set. Blocked air flow through the oil cooler, a blockage or restriction in the cooling hoses/tubes or an inoperative oil pump all contribute to poor cooling system performance."

We have an "R" model rear cover on order to see what we need to plumb it. We plan on designing it around a commonly available pump. We like the RB gear pump. Short of large pieces of metal passing through it, it will always pump oil. While running on track, pump noise is not really a concern. We thought about incorporating the GT350 parts completely but that cooler only has air moving over it at speed and would require body work changes. It is controlled through the PCM so we would still have to incorporate a temperture curve to operate it. We like switches and relay's, they either work or don't.

It also only adds about 400mL of fluid capacity. Total System Capacity is max about 1.9L vs. 1.5L for the non-cooled cars. We will incoroporate a separate temp switch so the factory sensing system is not effected.

We intend to incorporate a fan/cooler package so we know it has airflow and run it off a temp switch with a manual override. This way a heat soaked car can cool down the fluids between sessions.

It's coming but we need to make sure it works and is plug and play. Hope to release it this summer.
Rear Diff Cooler.jpg
 

GTBOB

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In the "A Faster Horse" documentary movie about the 2015 Mustang design and testing, the engineers talked about the rear diff had elevated temperatures to sort out. Ford knew about this from the get-go.
 

Niz55

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Little off topic. I jave 2016 gt non pp. I do have the slot on the diff to add the sensor but I couldn't find the harness under the car. Are the harness different from a pp and non pp?
 

steveespo

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'16 GT PP covers are tapped and plugged for the cooler lines. I am in for a kit when available. Does anyone know the part # for the Ford cooler matrix?
Steve
 

Brent Dalton

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P188A Differential Oil Temperature Too High / Too Low:

This DTC sets in continuous memory when the differential oil temperature exceeds 145° C (293° F).

Brent, I don't know if you scanned your car after the warning came up but I am looking everywhere in the service manual but nothing is mentioned for the Diff Temp other than Shelby Temp Warning. Maybe it is the same but they do not appear to have a gauge for it like we do for EOT in the GT. I'm not sure what threshold voltage is used for turning the GT350 cooler pump on. If your Ford friend could enlighten us we would appreciate it.

Normal Operation and Fault Conditions

"When the differential oil temperature reaches a predetermined level, the PCM grounds the differential oil pump relay which activates the differential oil pump. Once the oil temperature is reduced to another predetermined level, the PCM stops grounding the relay. While the relay is activated, the PCM continues to monitor the differential oil temperature and expects to see a reduction in the temperature. If the PCM does not see a reduction in the temperature or if the temperature continues to rise, a DTC is set. Blocked air flow through the oil cooler, a blockage or restriction in the cooling hoses/tubes or an inoperative oil pump all contribute to poor cooling system performance."

We have an "R" model rear cover on order to see what we need to plumb it. We plan on designing it around a commonly available pump. We like the RB gear pump. Short of large pieces of metal passing through it, it will always pump oil. While running on track, pump noise is not really a concern. We thought about incorporating the GT350 parts completely but that cooler only has air moving over it at speed and would require body work changes. It is controlled through the PCM so we would still have to incorporate a temperture curve to operate it. We like switches and relay's, they either work or don't.

It also only adds about 400mL of fluid capacity. Total System Capacity is max about 1.9L vs. 1.5L for the non-cooled cars. We will incoroporate a separate temp switch so the factory sensing system is not effected.

We intend to incorporate a fan/cooler package so we know it has airflow and run it off a temp switch with a manual override. This way a heat soaked car can cool down the fluids between sessions.

It's coming but we need to make sure it works and is plug and play. Hope to release it this summer.
Good info. I'll see what I can find out about what temp triggers the cooler to turn on.

In the "A Faster Horse" documentary movie about the 2015 Mustang design and testing, the engineers talked about the rear diff had elevated temperatures to sort out. Ford knew about this from the get-go.
I need to watch that. When I was back home at easter, my dad turned it on, but my daughter was having a rough night and didn't get to watch.

Little off topic. I jave 2016 gt non pp. I do have the slot on the diff to add the sensor but I couldn't find the harness under the car. Are the harness different from a pp and non pp?
You might check the parts schematics on someone like levitown's site to see.

'16 GT PP covers are tapped and plugged for the cooler lines. I am in for a kit when available. Does anyone know the part # for the Ford cooler matrix?
Steve
Nice! I've been busy with other stuff and haven't really dug into any of this yet. I have an time trial this coming weekend and will need to change my fluid out at some point this week. I figured I'd start trying to figure stuff out then. I'll snap some pictures and post them in this thread if no one else has by then.
 

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