I am running a supercharger, about 1200 pounds in aftermarket add-ons (bumpers, winch, roof rack, skids, yeti 1000, drawers, fridge... maybe more than 1200 honestly). When fully loaded for going out on trips I am assuming I am near 2000 pounds or more with myself, son, dog, a bunch of gear and usually 12 gallons of extra fuel and 10 gallons of water.

I installed CSF's radiator which got my engine temps to be between 190-198 at all times (used to run higher) but they claimed their system will lower my tranny temps. It did not and there is no one to talk to there as they don't design their systems nor have anyone with technical knowledge (I've called them)... they just order from China and put their sticker on.

In addition to CSF I installed a tranny cooler which dropped everything by about 10 degrees. I then added a fan to cool down the tranny faster when taking breaks offroading.

So my tranny temps are as follows:

180 - 205 daily driving with no gear.

220 - 230 highway driving on passes.

200 - 240 fully loaded on trips. Driving from Upland to Needles to jump on Mojave trail this weekend I basically stayed between 220 - 240 the entire trips after climbing the first pass near Cleghorn... basically those temps maintained for 3 hours or so. Please keep in mind I was averaging 83 MPH... so I KNOW I can slow down... but I'm trying make it so I don't have to.

220 - 250 when offroading at speeds. Between 45 - 65 MPH in sand or on dirt (basically most of the Mojave trail)... I'm up to 250 in no time. I ended up being in 230 - 250 for about 3 straight hours day 1 on my last trip and 5 straight hours day 2.

My question is how bad is this? Are these temps going to beat up my tranny and do I need to find another solution or is this OK? I am cool to change out tranny fluid every 10-20K miles as a solution?

BTW... please keep in mind that this is not my daily driver rig. 80% of my miles are either fully loaded going to trails or on trails. Therefore it seems like 60% of my miles will be between 220 - 250 at this point as I can't figure out how to get tranny cooler (other than slowing down... but if I wanted to drive slow... I would have stuck with my Jeep).

I just put my 34's on this past weekend, and monitored my temps up in the hills as it was a concern of mine coming up from a 3rd gen. It never went over 200 degrees but besides the suspension I'm still stock in terms of added weight. You've done just about everything you can to help out with temps. I've never had a vehicle with that much weight, but it was my understanding that temps over 230 would basically fry the oil. I didn't mind changing the oil out all the time in my 3rd gen, but it would get up to that just from hill climbing up in the mountains(high mileage tired engine and tranny). After every track day in my cars I would change out the tranny fluid because it would be in those temp ranges for the race day. Don't know if this helps any, hopefully the fully built overlanders with the weight can chime in. To me I'd think it would wear down the life of the tranny if you weren't going to change out the fluid every 10k at least.

Are you just leaving it in Drive when you're going up and down hills? Usually if I control what gear I am, I can prevent it from unnecessarily shifting and shooting the temp up. I can stay under 200 degrees while driving the passes in Colorado.

No... try to go lower gear but it’s a battle as I’m already getting 11 MPG so going in lower gear when it’s flat is tough mentally. I’m usually only in lower gear uphill.

But off-road is a bigger issue....

I used up a full tank plus 8 gallons out of spare 12 gallons that I took out on a three day trip this weekend (all off-road). If I’d be in lower gear when tranny was hot... I’d probably run out of fuel.

So I put in the csf when I did my supercharger. I also added a tranny cooler with fan. I have a steel rear bumper with swingout. Roofrack. Fridge. Dual batteries. Winch with steel front. I have full aluminum skids. I am on 33s. I am in so cal and see 170s in the morning. The last week I have been around 190, it has been in the high 90s to 100. When I tow my adventure trailer I am in the low 200s. I am very mindful of my gear choices when loaded or towing and it helps a ton. I am glad to hear I dont get as hot as you but I too hoped the new radiator would keep my Temps under 200.

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For my taste, those temps are high.. meaning I'd stick to the scheduled ATF fluid swap every ~62k miles or whatever the funny figure was in the manual..

Being in Kuwait and sand off-roading (modded 4runner with tires, steel, bumper, jerry cans, roof rack, trip gear...etc) I do see 210F and above frequently on my longer trips.. unloaded I'm around 190F to 205F most of the year (except summer since it's stupid hot out here)

Did the ATF swap and made a world of a difference!

I also stick only with the Toyota ATF and change the metal mesh filter while I'm at it.. $$ but worth it IMO

At the risk of sounding like a jerk...

... If you are really carrying a full ton (2,000 pounds) of added gear and accessories, you're waaaayyyy over GVWR for your 4Runner. My guess is that the transmission torque converter isn't able to lock up much, if at all, with the added weight... which will cause your tranny fluid to run hot like it is, and contributes to poor fuel economy - not to mention way more general wear and tear on the other drivetrain components. Especially if you are pushing your overloaded 4Runner at those highway speeds.

A larger auxiliary transmission cooler might help... but I might first suggest you figure out a way to jettison some of the extra weight you're carrying. And you might want to slow it down a bit, especially with being so far overweight.

Please be safe.

Personally 220F is where I get concerned. I'm not concerned about 220 assuming it is for limited time, but I wouldn't want to be at 240 or 250 for extended periods of time.

It's worth mentioning that transmission fluid manufacturers are comfortable up to 280 degrees, and so is Toyota as I don't think the transmission temp idiot light comes on until about 300 F

When off-roading if you're in 4hi I'd try dropping into 4lo. On occasion when sand is really soft here my temps will start to creep up in 4hi but I drop into 4lo and they drop right back down. I've never had high trans temps on trails in 4lo, even in stop and go crowded trail conditions in summer.

Basically what I expected to hear. Thanks for everyone’s input.

Will just deal with it and when it blows up... will see about putting a v8 into this thing. ;)


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How about 2 trans coolers and a 160* engine thermostat, instead of the stock 180* stat.

sounds like you need a vehicle along the lines of a power wagon

I'd definitely run a AUX cooler.

I have debated running the fluid only through the tranny cooler instead of the radiator and tranny cooler. Not sure if it would make much of a difference though.

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Your temps seem unusually high. There seems to be a correlation between supercharger and transmission temp/heat soak problems. - you're not the first person on here to have transmission temp issues after adding a supercharger.

As an example I tow a small camper - but it has a fairly high wind profile. Two weeks ago I went into a 25-30mpg headwind headed to southern Utah. For periods of time I was literally pedal to the floor and only able to maintain ~70mph WOT. I do have a medium size transmission aux cooler, but I never really thought it was necessary - mostly an extra precaution. I've never been able to get the temps on the transmission or engine to climb out of the typical operating ranges.

I can take random guess about the supercharger tune and the transmission's torque converter that has a intermediate "partially locked" option and where it might generate a lot of heat with more input torque than it thinks it's getting, but that's just a guess on my part. This might be a case where regearing the diffs could help reduce the torque in the transmission and lower temps.

Didn't want to do that to be honest (or even add a second tranny cooler) as it goes both ways. On the streets and flat ground it warmed up normally (time-wise). Once I added aux tranny cooler it took longer to warm up. But tranny cooler didn't really help it jumping from 190 - 230 in minutes once I hit passes or ride hard offroad. Tranny cooler just helped cool down faster.

So I figure if I add 160 thermostat, second tranny cooler, or run fluid only through aux coolers and not radiator... It may take 20 minutes of driving to get it up to temps and may not do much better on passes when I go from 190 - 230.

I think it's a bandaid that may hurt me more than help (but maybe I'm wrong)...