"Rear Axle Differential Temp Increased, Decrease Speed" warning

[NightmareMoon]

There is a setting in the config for "Rear Diff Temp" which is enabled by default. I'm wondering if turning that 'off' would disable the limp mode, basically by making the car ignore the sensor.

Someone would have to get their diff overheated to try it though, and they'd need fast access to a laptop, the OBDLink MX, and FORScan. Mine has yet to overheat, so IDK.

Let us know if you figure out if its due to NGauge or some issue with the sensor. It would be interesting if these sensors turned out to be flakey.

Sponsored

 

[pstoppani]

My understanding is that the car does NOT go into limp mode.

 

[Impulsed7]

Only way I have gotten "limp mode" was from a DTC for oil overtemp, when the ecoboost doesn't even have an oil temp sensor. Its inferred from the coolant temp and other variables. Even then, my limp mode was a 6K rev limiter for less than 15 seconds or so

 

[Brent Dalton]

My understanding is that the car does NOT go into limp mode.

It does go into limp mode. You get the first warning at 293 degrees to give you the heads up. If you continue to push, I think it's 300 degrees that it goes into limp mode(don't remember off the top of my head, but it's close to that). Only th 16+ GT performance package cars and track package GT350 have the sensor. Not an issue on the track pack GT350 as it has a cooler from the factory. So 8ts only really on 3.73 torsen diffs... so it makes some of us wonder... is it overheating due to the torsen and the regular type diff's don't suffer the same? A few guys like plimmer are working on the answer.

 

[steveespo]

Brent are you sure it goes into limp mode? I have run through both warnings on track and haven't lost power. Wrench comes on with "see Owners manual" warning but keeps power. I have gone into limp due to CHT temp of 245, that shuts it down to a crawl.
Steve

 

[EXP Jawa]

So 8ts only really on 3.73 torsen diffs... so it makes some of us wonder... is it overheating due to the torsen and the regular type diff's don't suffer the same? A few guys like plimmer are working on the answer.

A couple of comments - LSD's are friction devices. The higher the TBR/locking effect, the more friction it generates. So, the Torsen in this car, with a TBR of around 2.8:1 (versus 1.8:1 for Traction Lock), does create more friction.

However, with all of that said, friction only creates heat when you force slippage of those friction surfaces under high load. I think that if you could actually watch wheel speeds during track events, you'd be surprised by how little differentiation occurs, at least under load. At that TBR level, the Torsen isn't allowing the wheels to change speed much, even if it continues to bias torque side to side as required.

In general, in track use under high torque loads, the TBR level is sufficient to prevent most differentiation. If you have a plug-in system that's interacting with the vehicle CAN, see if you can pull the rear wheel speed sensors and see what actually goes on during a hot lap. You might find it interesting.

Anyway, the differentiation level is low, and even when it does, the differential rate (referred to as delta-N) is also quite low, on the order of 15-20 RPM difference from side to side. So the frictional heating that the differential contributes to the axle oil is pretty low, compared to the system as a whole. You get a lot more heat generated by the ring and pinion due to the hypoid mesh, and that is running constantly, at high speed. Past that, most of the heat probably comes from external sources - like the proximity of the exhaust, as already discussed. Combine that with the fairly small colume of oil available to absorb heat, and you get the situation you're in.

IMHO, the biggest reason that Ford monitors axle temp on PP cars isn't because the Torsen creates more heat, but rather because they see a greater need on those cars due to the perceived (track) usage. In their minds, the non-PP GT models are much less likely to be on the track, so they don't need to spend the extra couple of bucks to fit those cars with the sensor.

Just my $0.02...

Incidentally, I think I may repeat this question/answer on our blog once its up & running, with your permission Brent.

 

[Brent Dalton]

Brent are you sure it goes into limp mode? I have run through both warnings on track and haven't lost power. Wrench comes on with "see Owners manual" warning but keeps power. I have gone into limp due to CHT temp of 245, that shuts it down to a crawl.
Steve

Steve,
I'd say you are right. I thought GTF1 reported it going into limp mode on the secondary warning, ending his day at Road Atlanta. Sounds like I am rembemering incorrectly.

 

[Gatorac]

Brent are you sure it goes into limp mode? I have run through both warnings on track and haven't lost power. Wrench comes on with "see Owners manual" warning but keeps power. I have gone into limp due to CHT temp of 245, that shuts it down to a crawl.
Steve

Is CHT a regular issue with an otherwise stock car?

 

[steveespo]

Jim
It only happened once at Road America, we ran open track on a Thursday and I put in about 4 hours that day, 90 degrees and was chasing Nick in the 350R (not catching, but chasing) car just got hot and pulled power along with a drivetrain protection warning. I just coasted down to turn 5 and exited for the garage, car was back under normal power by the time I got off track. I am adding an additional air to oil cooler to help take the load off of the stock heat exchanger.
Steve

 

[Gatorac]

Jim
It only happened once at Road America, we ran open track on a Thursday and I put in about 4 hours that day, 90 degrees and was chasing Nick in the 350R (not catching, but chasing) car just got hot and pulled power along with a drivetrain protection warning. I just coasted down to turn 5 and exited for the garage, car was back under normal power by the time I got off track. I am adding an additional air to oil cooler to help take the load off of the stock heat exchanger.
Steve

I did some more searching and saw the RPM's your running. Now I understand why your car sounded like a GT350 down the front straight at MO.:hail:

I'm very close to pulling the trigger on a 2nd GTPP. One for myself to replace my BRZ. Just making sure I've covered all the basis on the weak points of the car on track.

 

[steveespo]

I did some more searching and saw the RPM's your running. Now I understand why your car sounded like a GT350 down the front straight at MO.:hail:

I'm very close to pulling the trigger on a 2nd GTPP. One for myself to replace my BRZ. Just making sure I've covered all the basis on the weak points of the car on track.

Wait till you hear it at the Glen, American Racing 1 7/8" long tubes and full 3" exhaust. I will be wearing earplugs under my helmet.:ford:

 

[Gatorac]

Wait till you hear it at the Glen, American Racing 1 7/8" long tubes and full 3" exhaust. I will be wearing earplugs under my helmet.:ford:

I'm there dude. If I do pull the trigger, I'll be picking my new GTPP up the day before Pitt and then driving it to WG. It will be very stock...

 

[Optimum Performance]

Brent are you sure it goes into limp mode? I have run through both warnings on track and haven't lost power. Wrench comes on with "see Owners manual" warning but keeps power. I have gone into limp due to CHT temp of 245, that shuts it down to a crawl.
Steve

Steve,
I'd say you are right. I thought GTF1 reported it going into limp mode on the secondary warning, ending his day at Road Atlanta. Sounds like I am rembemering incorrectly.

You should only get this:

P188A Differential Oil Temperature Too High / Too Low
This DTC sets in continuous memory when the differential oil temperature
exceeds 145° C (293° F).

And it applies to all 3.73 cars. Over in the Shelby threads someone got their cooler equipped car to 300+ on the rear axle. Pretty sure they should just put the old 75W-140 back in the 3.73 cars from the factory.

 

[ANGST]

Anyone catch this thread ? Pretty interesting , and related ?


http://tinyurl.com/zjgelc7

 

[Optimum Performance]

It appears BG Products is Recommending 75W-140 for our cars as well...but the BG Service Centers also offer Lifetime Driveline Services so that may have something to do with it along with meeting the Ford Spec.

LINK to my post in another thread.

Sponsored