Gearbox Overheating & Clearance Issues with T4R 21 TRD Off-Road in Desert Conditions

Hey everyone,

I’ve got a 2021 4Runner TRD Off-Road, and I've done a few mods to enhance performance. Here’s a rundown of what I’ve added:

• Airaid intake
• Larger throttle body
• Modified Intake Air Surge for bigger intake air flow
• Upgraded exhaust system
• Heavy-duty gears
• C4 bumper

While it runs great on highways, I’m hitting some issues when I take it off-road, especially on desert terrain here in the Middle East. When driving at higher speeds, my gearbox tends to overheat—even with two gearbox coolers, it reaches around 91°C. I'm worried that this could damage the gearbox over time.

Also, on rough terrain, the C4 bumper clearance causes it to hit pretty hard, which is a concern.

Has anyone experienced similar issues or found solutions for these problems? Any advice would be much appreciated!

 

91 C is 195.8 F, I don’t think that’s too high at all for transmission/gearbox temperature.

I think the warning comes on at a (too high?) 300 F.

Don’t worry about that temperature reading. If you’re in the mid-200’s then think about dialing it back or using 4Lo if you aren’t.

Regarding clearance, if the bumper is scraping at low speed consider picking different lines or maybe the vehicle is too low overall.

Your description is pretty vague so it’s hard to offer input since your bumper doesn’t look particularly low.

 

Yeah. Everything I'm finding gives a generic range of 175-200 F. So you're right there.

 

You actually don't want it cooler. A quick google

 

Thanks for the insights!

I usually drive in 4Lo when I’m off-road, and on regular streets, the transmission temp stays around 185°F. The overheating mainly happens when I’m pushing it on rough terrain.

As for the bumper clearance, I’m noticing more scraping when I hit dips at moderate speeds, especially on uneven ground. It seems to be the bumper hitting hard in those spots.

 

You shouldn't be in 4lo unless you need to. Same with the locker or 4hi.

Yes. Especially with i creased speed the force downward in a dip or bump can overpower your springs.

 

Sorry, usually I drive in 4Hi but not all the time.


Thanks for the advice!
I usually drive in 4Hi, but not all the time. I hadn’t thought about how increased speed over dips might overpower the springs, which makes sense. I’m currently using King springs—any suggestions on adjustments or ways to fix the clearance issues?

 

By clearance issues you need dips and bumps in the road at higher speeds?

No way around that except for like baja race truck.

4runnet and regular vehicles just aren't meant for it. They will bottom out when you go too fast over rough road. And sometimes that's still pretty slow depending on the road. Just gotta slow down for bumps and dips.

Very cool looking 4Runner tho. I've seen some posts on reddit from people in the Middle East. Are these getting more popular over there?

 

a few degrees difference is nothing in this case, you’re fine, I promise.

Are you saying that the scraping did not happen before the bumper was installed in the same driving conditions?

 

Thanks for the info!

In the desert terrain here, high speeds are sometimes necessary, especially for climbing steep sand dunes, which makes dealing with clearance issues important. Slowing down isn’t always an option if I want to keep momentum in those situations.

And yes, the 4Runner has really gained popularity in the Middle East! There are a lot of off-roading groups and events now because it’s such a fun vehicle to take on rough terrain.

 

Thanks for the reassurance!

Here in the midday heat, temperatures can reach up to 140°F, which definitely seems to add to the gear temperature.

As for the bumper, it was fine before, but installing the C4 required adjustments and cutting part of the bumper. Now, on rough roads, that cut area hits and scrapes more frequently, causing quite a few collisions.

Any thoughts on how to minimize the impact or adjust the setup?

 

I believe you are describing the plastic body panel rubbing against the metal viper cut bumper. That would be caused by body mounts relative movement compared to frame mounted bumper. Also, frame flex could push the two against one another.

 

Thanks for confirming. It does seem like the plastic body panel is rubbing against the metal bumper due to movement between the body mounts and the frame-mounted bumper.

Has anyone found any effective solutions to this problem? I would really like to find a solution if possible. Thanks

 

Do you air down in the sand, might help in not needing so much speed, particularly in deep soft stuff. But then you do loose a little ground clearance, but not much

 

Normally, we air down to 20 or less when driving in the sand. It helps with traction, but as you mentioned, it does sacrifice a bit of ground clearance.

Thanks for the suggestion!

 

Nice 4R and looks great.

A few comments, once you start cutting the bumper (viper cut), the black fender flares you have, and other things, the remainder will flex. From one of the Pictures you can see there is a little gap so probably on the reinstall clips were damaged or shifted. Temp solution is to reinforce sections and you can DIY with zip ties or get a big boy bumper.
On the gears and the temp, this is more critical, I am lost on the upgrade etc. What exactly did you upgrade to from stock? What were the changes and what oils were used after the upgrades. I offroad in south Texas all the time, of course not sand or as hot as the ME, but it could get pretty hot here. I have a scangauge...and I never get over 220F on the transmission which is the one I worried about. I am always in 4Lo when out there in the sand or rocks.

 

I would air down even more. Try 15 psi. If you are spinning a lot in the sand this could contributing to the overheating you are having.

 

Thanks for the tips! I may need to fill those gaps with silicone and reinforce any loose sections to reduce the flex. I’ll look into a more permanent solution down the line, but that should help for now.

For the upgrades, I modified the air intake and exhaust for higher airflow than stock (keeping the headers stock), so there's a bit more back pressure in the exhaust, which may be limiting performance. For oils, I used Toyota oils and added Lucas anti-squawk oil.

 

You need ti stiffen up the compression on those coilovers somehow

 

good point. Are the coolers getting clogged up and decreasing cooling effect?

 

Are you running stock bump stops front/rear? If yes, that is contributing to you bottoming out

 

Manually shift the shifter over to the 4 instead of leaving it in overdrive. If you are pushing hard like in the sand at higher RPM maybe even shift to 3 manually. This keeps the trans from shifting in the higher gears. Being in a higher gear ratio, under loads, generates higher trans temp. This is the same when towing, if you are towing on the highway and its flat, you MIGHT can run overdrive but if you are towing and there are constant rolling hills, you need to run in a lower gear ratio. The hill climbs in higher gears generate tons of load and tons of heat. Example, while running flat ground towing in normal overdrive you might see 185degrees trans temp but on a hill climb where its just enough load that you bog down a little, but not enough to make the trans downshift, you will see the trans temps climb from 190 up to about 220-230 degrees on a bigger climb. Bogging down in a higher gear will generate tons of load and lots of temp quickly. You can manually slap the shifter down into a lower gear ratio to reduce the gearing and reduce the load. If you are somewhere that is pretty sandy that presents a high load, try manually shifting the shifter in a lower gear to keep the RPM up, and the load off the trans.
Also for the bottoming out, yes in higher speed large whoops the front end cant control itself adequately and you will bottom out, maybe look into the slapper bump stops Camburg makes, this helps slow things down on the big G-outs.

https://www.camburg.com/products/ca...2-5-camburg-series-bump-stop-kit-cam-310172-2
https://www.youtube.com/watch?v=hlkeEJ6BZeI&ab_channel=CamburgRacing

 

Oh. Running hard in the sand and dunes. That makes a lot of sense. That's really cool you're running your 4Runner that hard!

People that do that usually run bumpers like this
https://www.4runnerlifestyle.com/products/c4-4runner-2014-current-hybrid-front-bumper

And as someone else suggested, stiffening your shocks.

Or a long travel set up would help a lot. Replacing the a-arms. I don't know much about that.

 

Just realize that you can air down to the point the center of the tread can concave in toward the rim and pull on the bead seal. Then sharp turns and spinning can break the seal. Have seen it happen twice, once on 2 tires at same time.

Rule of thumb I learned from some desert rats decades ago, works for radials, not sure about others

With tires at recommended street pressure, loaded as it will be on the sand including people and on level pavement. Measure the height from pavement to bottom of rim.
lower pressure until height is 3/4 of street pressure. This gives the best flat footprint. Going lower provides only marginal improvement and raises risk of bead failure

 

From the pic it looks like OP is already on long travel in front. Agree on the suspensionadvice. Kings have lots of potential if set up cortectly.
@Khusaibi did you have your new suspension set up by a local specialist that knows your local terrain and how you run it? If not it’s probably worth the time and expense to have it set up correctly. You may need bump-stops to match as well, maybe even hydraulic bump stops.

 

I install the cooler less than one month and they are working fine in the street

 

I use after mark bump stop around 6 inch

 

Thanks for the detailed explanation!

I usually shift manually into 3rd gear when driving in the sand to keep the RPMs up and manage the load on the transmission. I might need to look into adjusting my King suspension too, as the bottoming out can get pretty rough on larger dips. I’ll also check out the Camburg slapper bump stops you mentioned—they sound like a good option for handling those big G-outs.

Appreciate the tips!

 

Thanks! I actually only drive at medium speeds on the sand, not too high. Unfortunately, those bumpers are not allowed here, but I really like the look of the C4 bumpers, so I went with that.

As someone else suggested, I’m considering strengthening the shock absorbers. For the arms, I’m currently using Total Chaos.

Appreciate the suggestions!

 

Thanks for the tip! I usually keep my tires at 15 psi to maintain their condition, and I’m using Mastercraft tires. I hadn’t thought about the risk of the tread concaving in too much or pulling on the bead seal—good to know.

I’ll try checking the height from the pavement to the bottom of the rim as you suggested and see if adjusting it to 3/4 of street pressure helps. Thanks again for the advice!