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Discussion Starter · #1 ·
Hello,

My first post here, we got an Ascent last week and took out our camper for a weekend trip. The "rdiff temp" light came on almost every 100 miles. Each time it came on I would pull over and let it sit for 10-15 minutes to cool off.

Tow info:
Coachmen Clipper 17bhs @ 3500lbs empty, 4300 pounds max (I plan to verify loaded weight before next trip)
Tow speed 65-70 mph on flat Nebraska interstates.
Weight distributing hitch
TV tires at 35 PSI
Trailer tires at 65 PSI

We took it to the dealer, and they said the differential fluid was dark (duh) so they changed it and told me to have the trailer weighed fully loaded. Considering the fluid was discolored I think that rules out a faulty sensor.

I searched and saw this has happened a couple other times, but no resolution has ever been shared. Thoughts?
 

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Weight distributing hitch
You need to stop using the WDH...Subaru prohibits them on the Ascent. Please read the extensive thread sticked at the top of the Towing discussion section.

You shouldn't be having that issue with the r-dif at all. I don't recall anyone else mentioning it, but I obviously could have missed it. Something is amiss and hopefully your dealer service folks can figure it out.
 

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Did you purchase your Ascent brand new or used (how many miles if so)? If brand new, I wouldn't expect the differential fluid to be dark / or causing any issues.

If used, it's possible that the differential fluid was at the end of it's service life which caused the increased temperatures under the stress of towing.
 
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Discussion Starter · #4 ·
You need to stop using the WDH...Subaru prohibits them on the Ascent. Please read the extensive thread sticked at the top of the Towing discussion section.

You shouldn't be having that issue with the r-dif at all. I don't recall anyone else mentioning it, but I obviously could have missed it. Something is amiss and hopefully your dealer service folks can figure it out.
I read the towing section in the manual before towing with it and didn't see anything regarding the WDH mentioned in the documentation. I'll look into that thread.

Did you purchase your Ascent brand new or used (how many miles if so)? If brand new, I wouldn't expect the differential fluid to be dark / or causing any issues.

If used, it's possible that the differential fluid was at the end of it's service life which caused the increased temperatures under the stress of towing.
Brand new. It had ~600 miles on it when we started the trip and ~1000 when we got back.
 

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I read the towing section in the manual before towing with it and didn't see anything regarding the WDH mentioned in the documentation. I'll look into that thread.



Brand new. It had ~600 miles on it when we started the trip and ~1000 when we got back.
Hi, some tips and possible answers...

Break In
You needed to complete the break in before towing. That was important. Do not tow until you complete a brand new 1,000 mile break in. Differential service restarts the thousand mile clock.

Causes of Diff Overheat:
Trailer brakes that are stuck, or an improperly calibrated brake controller.


The WDH thread is here:
 

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Discussion Starter · #6 ·
Hi, some tips and possible answers...

Break In
You needed to complete the break in before towing. That was important. Do not tow until you complete a brand new 1,000 mile break in. Differential service restarts the thousand mile clock.

Causes of Diff Overheat:
Trailer brakes that are stuck, or an improperly calibrated brake controller.


The WDH thread is here:
Thanks for the info.
 

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Hello,

My first post here, we got an Ascent last week and took out our camper for a weekend trip. The "rdiff temp" light came on almost every 100 miles. Each time it came on I would pull over and let it sit for 10-15 minutes to cool off.

Tow info:
Coachmen Clipper 17bhs @ 3500lbs empty, 4300 pounds max (I plan to verify loaded weight before next trip)
Tow speed 65-70 mph on flat Nebraska interstates.
Weight distributing hitch
TV tires at 35 PSI
Trailer tires at 65 PSI

We took it to the dealer, and they said the differential fluid was dark (duh) so they changed it and told me to have the trailer weighed fully loaded. Considering the fluid was discolored I think that rules out a faulty sensor.

I searched and saw this has happened a couple other times, but no resolution has ever been shared. Thoughts?
Yeah something isn't right. I towed my Mustang on a flatbed trailer (4,530lbs total) from Phoenix to Joshua Tree pretty much non stop in much higher temps and never had the light come on.
 
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I got rid of the WD hitch, double checked my brake controller (which seems to be fine), and had the trailer weighed per dealer instructions. Trailer is 3800 pounds loaded.

Waiting for 1000 miles to try it again.
Make sure you calibrate it with the trailer hooked up. We find a parking lot or straight stretch of road to get it right.
 

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Discussion Starter · #11 · (Edited)
Problem persists.
Steps I have changed since the issue first started:

Waited another 1,000 miles for the break in.

Got rid of the WD hitch and using a standard drop hitch with the riding trailer level.

Calibrated brake controller with trailer loaded. Appears to be operating correct and the same as any vehicle I have used before.

Reweighed trailer and adjust load to balance the trailer better. Weighed 3600 pounds this time (I left my fishing gear at home 🤣)

Last time I took it in they replaced the dif fluid and said it was dark. This time they are saying they might bring a corporate tech in to look at it and they want the receipts from the scales.

Anyway, not happy with this purchase so far. Two ruined weekends and losing my last long camping weekend of the year really sucks.

trying to fix typos on mobile.
 

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Discussion Starter · #12 ·
Could this be caused by excessive tongue weight? I have had this trailer weighed many time by now, and Subaru isn't going to be any help regardless of me being far below the allowed weights.

The only weight that is even close is the tongue weight at 480 pounds.
 

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If I were to speculate, I'd doubt it. While I have a lighter tongue weight (even with my heavier trailer, because the water is balanced between the two axles), I am sure others tow with near that, like @Kevin Williams.

Are you leaving the car in full automatic? No ACC, no manual shifting, no X-Mode, VDC on? Are your tires the same brand and size and inflation?

A rear differential generally overheats due to the following causes:
  • Different size or inflation tires (different types/brands of tires of the same number code size can be different circumferences, btw).
  • Bad wheel speed sensor causing improper VDC operation (really really rare - the wheel speed sensor is usually detected as bad, and a code will be thrown - and in the really rare cases, you'd usually get a lot of "VDC active" flashes on the dash board.

Has Subaru of America been involved?

Could this be caused by excessive tongue weight? I have had this trailer weighed many time by now, and Subaru isn't going to be any help regardless of me being far below the allowed weights.

The only weight that is even close is the tongue weight at 480 pounds.
 

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Could this be caused by excessive tongue weight? I have had this trailer weighed many time by now, and Subaru isn't going to be any help regardless of me being far below the allowed weights.

The only weight that is even close is the tongue weight at 480 pounds.
I don't think that having the tongue weight close to the max but still under would have caused the rear diff temp problems.

I think towing before break in is the likely cause. Gears really need time to mesh together before applying heavy loads.
 

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Discussion Starter · #15 ·
If I were to speculate, I'd doubt it. While I have a lighter tongue weight (even with my heavier trailer, because the water is balanced between the two axles), I am sure others tow with near that, like @Kevin Williams.

Are you leaving the car in full automatic? No ACC, no manual shifting, no X-Mode, VDC on? Are your tires the same brand and size and inflation?
Full Automatic.
Don't know what ACC is...
Stock tires all @35psi cold.
VDC on.
A rear differential generally overheats due to the following causes:
  • Different size or inflation tires (different types/brands of tires of the same number code size can be different circumferences, btw).
  • Bad wheel speed sensor causing improper VDC operation (really really rare - the wheel speed sensor is usually detected as bad, and a code will be thrown - and in the really rare cases, you'd usually get a lot of "VDC active" flashes on the dash board.
Has Subaru of America been involved?
Subaru of America said they don't cover vehicle malfunctions due to towing, even if it is within the weight limit. The Dealer told me to talk to them and they won't talk to me.
 

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Discussion Starter · #16 ·
I don't think that having the tongue weight close to the max but still under would have caused the rear diff temp problems.

I think towing before break in is the likely cause. Gears really need time to mesh together before applying heavy loads.
Fair enough the first time, so unless the diff was ruined why is it still happening at 2,000 miles?
 

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Discussion Starter · #17 ·
They are saying the following factors are causing this:
Close to GVWR weight limit (close, but not over)
Wind Resisitance (7ft wide camper)
90 degree ambient temp
Slight Uphill Slope

Weights are as follows:
Front axle: 2460
Rear Axle: 2720 (Includes 480 pounds of tongue weight)
Trailer Axle: 3240

This leaves 820 pounds for family and dog in the car and 1700 pounds for food and clothes in the trailer.

I also had it weighed full (trailer only) and it was 3620 with all of our shit in it. We don't pull it with water.
 

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Subaru of America said they don't cover vehicle malfunctions due to towing, even if it is within the weight limit. The Dealer told me to talk to them and they won't talk to me.
That does not make sense. If you are within the manufacturer's requirements for towing it should be covered.

Fair enough the first time, so unless the diff was ruined why is it still happening at 2,000 miles?
The gear teeth could have been damaged / galled while towing before they had a proper breakin.
 

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Discussion Starter · #19 ·
That does not make sense. If you are within the manufacturer's requirements for towing it should be covered.



The gear teeth could have been damaged / galled while towing before they had a proper breakin.
That's what I said but, from Subaru of America:
“Subaru warranties do not apply to vehicle damage or malfunction caused by trailer towing. If you use your vehicle to tow a trailer, more frequent maintenance will be required due to the additional load. Under no circumstances should a trailer be towed with a new vehicle or a vehicle with any new powertrain component (engine, transmission, differential, wheel bearings, etc) for the first 1,000 miles of driving.” pg. 396 Section 8-12 of the Owner’s Manual
It doesn't say improper trailer towing, it just says trailer towing.
 

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That does not make sense. If you are within the manufacturer's requirements for towing it should be covered.
Per the Owner's Manual, the warranty specifically excludes damages caused when towing. Most warranties seem to for such classes of vehicles.
 
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