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I'm all but converted to the GRC from my previous GR86 preference. The only thing I am having trouble predicting is the GR-FOUR systems possibility of overheating on track. I'll be wanting to use this car for everything, including ~6 track days a year. Now, I know there's a lot of predicting and speculation about specifics on the GRC some members don't like here, but if the GRC is unable to run on 15-20 minute track sessions in California weather, I'll likely have to go back to the GR86.

I was hoping to find at least a somewhat definitive answer on the GRY forums, considering the AWD system is the same on the GRC, but I am finding conflicting answers. Many report the overheating issue coming up after donuts and drifting, which I don't care about. Some members say they have no issues with tracking, others also report overheating after a track day. There are plenty of videos on youtube of the overheating message on the screen it just has me worried.

Some remedies I've read about are the larger Cusco diff backing plate, which increases capacity from 500cc to 750cc. Another is heat wrapping a section of the exhaust pipe nearest to the diff/clutch system. And the last is comments from toyota during the unveiling that air will be better routed to aid cooling.

With the above aids, do you think the overheating will be a nonissue? Do we think a cooler might be developed? What do you guys think?
 

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I currently have a 22' GR 86 and have done three track days with it. Falcon RT660, Ferodo DS 1.11 pads, camber and good fluids and she has been great even for 30 min sessions at a test and tune day with a race team at full pace. The 86 platform is really solid for a track car that is also a decent little street car.

I have the #1 spot at my dealer for a new GRC, and instead of a track car that is a decent street car I believe it will be a great street car that can also survive limited track use. The engineering behind the GR-Four awd system is that the clutch coupling is always slipping since the rear diff is 1% overdriven. I suspect going to the 30/70 split most of us would prefer for track use is done by clamping the clutches tighter which in turn generates even more heat?

In the GR Yaris the problem seems to vary in severity, I believe because of the variables with how hard the car is being driven, wide and sticky tires seem to make it worse, and certain track configurations may contribute.

Either way I believe the aftermarket will eventually come up with a solution. It seems an external cooler for coupling or differential is the logical choice but since they are not widely available for the GRY yet makes me think it isn't just as easy as slapping an air to oil cooler on the back (space limitations, need for pump, access to fill/drain holes to get access to fluid, etc).
 

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We can't know for sure. We know the GRY suffered from overheating, and we've got video evidence of it time and time again. That said, I trust Toyota has seen the issue and worked to resolve it in the GRC.

Even if they don't, you can almost guarantee that the aftermarket will.
 

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I'm all but converted to the GRC from my previous GR86 preference. The only thing I am having trouble predicting is the GR-FOUR systems possibility of overheating on track. I'll be wanting to use this car for everything, including ~6 track days a year. Now, I know there's a lot of predicting and speculation about specifics on the GRC some members don't like here, but if the GRC is unable to run on 15-20 minute track sessions in California weather, I'll likely have to go back to the GR86.

I was hoping to find at least a somewhat definitive answer on the GRY forums, considering the AWD system is the same on the GRC, but I am finding conflicting answers. Many report the overheating issue coming up after donuts and drifting, which I don't care about. Some members say they have no issues with tracking, others also report overheating after a track day. There are plenty of videos on youtube of the overheating message on the screen it just has me worried.

Some remedies I've read about are the larger Cusco diff backing plate, which increases capacity from 500cc to 750cc. Another is heat wrapping a section of the exhaust pipe nearest to the diff/clutch system. And the last is comments from toyota during the unveiling that air will be better routed to aid cooling.

With the above aids, do you think the overheating will be a nonissue? Do we think a cooler might be developed? What do you guys think?
Isn’t the overheating issue with the center Coupling not the rear differential exactly? Unless they share fluid (I don’t think they do) I’m not sure How increasing the fluid capacity of the rear diff benefits the Coupling?
 

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Preliminary "Google Foo" results of my searching this morning for "GR Yaris AWD overheating". Some folks point to the problem being the temperature sensor in the clutch housing that's in front of the rear diff. The recommendation is to wrap the exhaust near the clutch housing, and it lowers the temperature of the clutch packs. The 2nd recommendation is to install a Cusco rear diff cover that allows more fluid to be added.

Here's a video of the cheap fix.
 

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I mean if your doing AWD axle spins then that's on you haha. I wouldn't be too concerned about regular grip driving overheat issues. From what I can tell, they don't seem to lead to GRY mechanical failure. Some heat blocking addons and a higher volume diff cover sound like great easy solutions.
 

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I mean if your doing AWD axle spins then that's on you haha. I wouldn't be too concerned about regular grip driving overheat issues. From what I can tell, they don't seem to lead to GRY mechanical failure. Some heat blocking addons and a higher volume diff cover sound like great easy solutions.
There’s people on the GRY forums who have said it happens in daily driving as well. Just one of the things you have to deal with.

They do have cooling options like you’ve stated.
 

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I've also started researching the overheating issue on the GR Yaris and my findings so far are related to those running much wider wheels and tires (265+). I've only spent an hour or two reading through forums so far, but it could be something to keep an eye out for during your research. If people are reporting overheating front or rear diffs, I would question their wheel and tire setup.
 

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I haven't directly searched for it, but I've read build threads from a few GRY owners who have done a fair bit of track driving with no mention of overheating issues or making any changes to avoid having them.
 

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I'm all but converted to the GRC from my previous GR86 preference. The only thing I am having trouble predicting is the GR-FOUR systems possibility of overheating on track. I'll be wanting to use this car for everything, including ~6 track days a year. Now, I know there's a lot of predicting and speculation about specifics on the GRC some members don't like here, but if the GRC is unable to run on 15-20 minute track sessions in California weather, I'll likely have to go back to the GR86.

I was hoping to find at least a somewhat definitive answer on the GRY forums, considering the AWD system is the same on the GRC, but I am finding conflicting answers. Many report the overheating issue coming up after donuts and drifting, which I don't care about. Some members say they have no issues with tracking, others also report overheating after a track day. There are plenty of videos on youtube of the overheating message on the screen it just has me worried.

Some remedies I've read about are the larger Cusco diff backing plate, which increases capacity from 500cc to 750cc. Another is heat wrapping a section of the exhaust pipe nearest to the diff/clutch system. And the last is comments from toyota during the unveiling that air will be better routed to aid cooling.

With the above aids, do you think the overheating will be a nonissue? Do we think a cooler might be developed? What do you guys think?
Curious about this as well. I don't plan on making it my main track car, but I'd like to take it on a circuit occasionally and really let loose with it. What I expect tho, is overheating just like what other comparative hot hatches have experienced after a 20-30 minute session. These awd hatches are motorsport enough, but they're just too weighty and complex to handle the stress as well as the GR86 would. I'd keep that car on your list in case the GRC goes into limp mode sooner than preferred.

Aftermarket will provide solutions though, just like it did with the RS. Just need some patience and optimism haha
 

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Isn’t the overheating issue with the center Coupling not the rear differential exactly? Unless they share fluid (I don’t think they do) I’m not sure How increasing the fluid capacity of the rear diff benefits the Coupling?
I think they are shared, the coupling is bolted right on the diff.
 

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Preliminary "Google Foo" results of my searching this morning for "GR Yaris AWD overheating". Some folks point to the problem being the temperature sensor in the clutch housing that's in front of the rear diff. The recommendation is to wrap the exhaust near the clutch housing, and it lowers the temperature of the clutch packs. The 2nd recommendation is to install a Cusco rear diff cover that allows more fluid to be added.

Here's a video of the cheap fix.
If this is an issue on the GRY, I hope they address this on the GRC since it's heavier and a new car. I hope they have a bigger cover, some type of heat sink or additional ducting.

Wrapping it is a good option but temporary. If this is going to be an issue, I'd recommend getting the exhaust pipes coated.
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Discussion Starter · #14 ·
If it turns out the only real remedy toyota employs is the redirected air, the first thing I'll be doing is wrapping the exhaust around the differential area. I'll also be leaning towards trying to pick up the cusco large capacity diff cover. Something about my AWD system overheating, with some reporting through typical driving, has me wanting to be more safe than sorry.

I wonder if anyone has tried a heavier weight oil in the AWD system than factory, similar to how ND Miata guys, myself included, chose to forgo the stock 0W-20 engine oil (emissions/fueleconomy) for 5W-30 oil if tracking.
 

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They designed a cooler for the RS for the PTU/RDU. I sold my car and quit following the R&D in the aftermarket but one company made it. The RS’s I drove at their track day all had simple air scoop type coolers on the PTU and we beat those cars to hell all day long on the track and not one went into limp mode. And that setup they had on those was a couple hundred bucks and pretty simple. If the GRC succeeds as well as we think I’m sure someone will address it. I’d worry about something else.
 

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With stock sized (or close to it) sticky street tires I doubt it'll be an issue on track. R comps, however, you never know. But if you're taking that step there's a lot of items that should be modified on the car.
 

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With stock sized (or close to it) sticky street tires I doubt it'll be an issue on track. R comps, however, you never know. But if you're taking that step there's a lot of items that should be modified on the car.
It’s a issue that happens randomly for some or competitively for others with proper track setups. It’s been pointed out more in Japan from why I’ve seen by tuners and things
 

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It’s a issue that happens randomly for some or competitively for others with proper track setups. It’s been pointed out more in Japan from why I’ve seen by tuners and things
I'm just concerned because I track in 105-110F ambient temps through the summer. I feel like large capacity covers and cooling might end up becoming a necessity!
 

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I wonder if anyone has tried a heavier weight oil in the AWD system than factory, similar to how ND Miata guys, myself included, chose to forgo the stock 0W-20 engine oil (emissions/fueleconomy) for 5W-30 oil if tracking.
I will not be running 0W-20 oil out here, no need for it the winter temps are not low enough and not interested in a fraction of a percent fuel economy if 5W-30 is better for the engine life. We have a much better range of 5W-30 oil as well as that's what pretty much everything has been running for the last 20 years. We get super high end 5W-30 full synthetic oils from Mobil and Castrol that meet the highest spec for the Euro cars. If I was on the track with it I would lean towards even a 5W-40 oil.
 
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