Let's talk S550 rear differential temps

[Jwodon]

Happy Wednesday everyone. The weather is getting warmer here in the Northeast and we are about to begin the 2019 track season and I couldn't be more excited!

One thing that has been on my mind since last year has been the rear diff on my car. It is a '17 GT PP car with the 3.73 Torsen. Last year was my first year participating in track day events, so I had very few mods done to the car. After a few hot laps, I had an alert pop up on my dash saying "Rear Axel Differential Temp Increased, Decrease Speed." After this warning came up, I simply cut my session short and came in, experiencing no issues on future sessions or really any issues with my rear diff since. This warning popped up multiple times last year.

What have others done to compensate for the high temps in the rear diff? I know Full Tilt offers a differential intercooler kit, but this being only my second year tracking my car, I would rather use that $1000 on consumables (tires/brakes) and more events.

I also have read that others have simply just swapped the stock rear fluid out with 75W140 which is more sustainable under high heat.

Any info is appreciated

 

[docs302]

Hi Jake, and welcome! I'm in Downingtown so I may be running into you this season at some of the local venues. Although I have a 13 Boss and the tried and true stick axle the diff overheating is a common problem if you search other posts. The least expensive options are fluid upgrades as you mentioned and catch cans/breathers. I had a Bob's breather kit for last year but have now switched to a similar type of system made by Cortex as I have their Watt's link and diff cover. They also make systems that are mounted in your rear trunk like the race cars but that may not be desired for a street car. They are not expensive (under $200) and easy to install. They will at least keep the boiling fluid from getting all over your car and the track. A finned diff cover (if you don't have one already) can also add a little bit of heat dissipation. I have not had overheating issues yet but I also have not run much more than 20 min sessions. If it became an issue even after all of these fixes then I would have to look at the cooler.

 

[Jwodon]

Hi Jake, and welcome! I'm in Downingtown so I may be running into you this season at some of the local venues. Although I have a 13 Boss and the tried and true stick axle the diff overheating is a common problem if you search other posts. The least expensive options are fluid upgrades as you mentioned and catch cans/breathers. I had a Bob's breather kit for last year but have now switched to a similar type of system made by Cortex as I have their Watt's link and diff cover. They also make systems that are mounted in your rear trunk like the race cars but that may not be desired for a street car. They are not expensive (under $200) and easy to install. They will at least keep the boiling fluid from getting all over your car and the track. A finned diff cover (if you don't have one already) can also add a little bit of heat dissipation. I have not had overheating issues yet but I also have not run much more than 20 min sessions. If it became an issue even after all of these fixes then I would have to look at the cooler.

Thanks Doc! Hoping to see you out at a few events this year.

I am not aware that anyone makes a catch can or finned diff cover yet for S550's. I may just take my chances, swap the fluid out and maybe heatwrap the exhaust that hugs the rear dif? (not sure how effective that would be, but alas another cheap prevention measure).

Obviously as you mentioned the best solution would be the intercooler. Guess I will see how it is after my first event!

 

[venom52]

Lots of GT members here just bit the bullet and got the FTBR kit. If i had bought a GT that kit would have been my first purchase as it will only benefit the car and track time. I'm sure it's fine to run a couple of sessions without one but as you know the heat problem will only stay and keep your sessions short and possibly keep them getting shorter as ambient temps go up during day.

I know Vorschlag added the aluminium housing but they will eventually add the cooler to keep temps firmly in check.

 

[JDee]

I have '16 PP1 with 3.73s, I get it on hot days at Mosport. I have the BG 75/140 fluid which some folks think is a big help but it's not a solution IMHO. Only solution is to cut sessions short, I tend to only do 5 laps at a time on those days, in fact on most days that's what I do now. And also change the fluid a fair bit, though I think I am overdoing that, what comes out now looks like new fluid.

Heat soak between sessions is a big problem, the temp never comes down much and I don't believe the exhaust wrap is much help. A big fan blowing air under the car might help but I haven't tried that yet. I was thinking the FTBR kit but really don't want to add weight to an already porky car, even if it's at the lighter end. For now, shortening sessions is the best solution for me.

 

[Jwodon]

I have '16 PP1 with 3.73s, I get it on hot days at Mosport. I have the BG 75/140 fluid which some folks think is a big help but it's not a solution IMHO. Only solution is to cut sessions short, I tend to only do 5 laps at a time on those days, in fact on most days that's what I do now. And also change the fluid a fair bit, though I think I am overdoing that, what comes out now looks like new fluid.

Heat soak between sessions is a big problem, the temp never comes down much and I don't believe the exhaust wrap is much help. A big fan blowing air under the car might help but I haven't tried that yet. I was thinking the FTBR kit but really don't want to add weight to an already porky car, even if it's at the lighter end. For now, shortening sessions is the best solution for me.

As Mad302 mentioned above, seems to be one of the only solutions is to install the rear diff cooler. Unfortunately for me I will not be doing that until next year.

 

[Nvrfinished]

My differential suffers from the same issues. The higher weight fluid and wrapping my exhaust did help, but all it did was buy a few more laps. As has been stated, the only fix is the cooler kits. A finned differential cover is not going to do much because the differential does not hold that much fluid to begin with.

What's interesting is that I have yet to hear of anyone who has suffered seal failure or other problems due to the excess heat. I don't know if it's because everyone is being careful about it or something else. There are a lot of people with the 2015 S550's who track their cars without knowing when the rear differential over-temps.