High transmission temp.

Saturday I was heading up the WABDR section 2.5, temp was 73, rig was loaded for a few days camping.

as I got to the top of the first big hill I got a high temp on transmission. I parked and went on a walk.

It’s a steep rocky hill a few miles long. In 4h, second gear the last mile as it over babyhead rocks. Rig has 108k on it. It’s new to me. Had local shop do transmission fill and drain, transfer case and radiator. Had paperwork that both front and rear diff were done at 100k. I did oil myself.

Turned back as I was 4 hours from home. Rig did fine.

What would be the logical thing to check? The shop that did my work has been around for decades and highly recommend.

Should I ad an external cooler?

 

Yeah I would get a cooler. My stock sr5 4x4 in south Florida, unloaded in 2wd pan temps get around 185 and TC can reach 200-205 easily in stop and go traffic. To give you a baseline unloaded truck in traffic.

for the temp light to come on, it means the atf got hot, I think it’s 280? It comes on it? I’m not sure it could be higher, BUT, what I would do would be a couple “cold mornings” drain and fills with WS… just to get the cooked fluid out of there and to add some new fluid to circulate it around.
Do you have a Scangauge 2 or 3? Or just a regular obd2 scanner than can read temps? If so, you can do this in your driveway in under 1 hour. Depending on ambient temp.

drain cold, refill + 1/2 quart, start truck and monitor at pan temp. @ 104 open 5mm hex, drain excess WHILE truck is running, and fasten check up once you get the dribble /drip break in the stream to set the level. Repeat drain and fill every 750-1000 miles.

but you don’t want to overdue it. It comes with some friction modifier, but you need some grit from the “old fluid” so it doesn’t prematurely slip on you


Edit; I see you have your shop you like. I’m sure they would install a atf cooler for you, and do a drain and fill for you. But the life expectancy of ATF fluid drastically decreases with heat. Especially if the light came on

 

OP, I am confused. What units are you using degrees C or F? What temperatures have you seen before? What tire size are you running? Are you regear?

 

Fahrenheit.
ive only put a few thousand miles on it, some fire roads, mostly pavement before this. No re gear. 285/70/17

 

Recommendations on a specific cooler?

 

Well, a few things come to mind, did the shop use the correct transmission fluid, this is a touchy issue, ATF is what these trannys like and others sometimes don't do well. When you were pulling up, were you in 4H or 4Lo? If you were on 2wd and going up and heavy loaded....the tranny will work more. I don't think you need to run a cooler on these units. Find first details on what was used on fluids etc and then re-evaluate. Many of us run with many heavy loads and even pulling trailers and dont have tranny issues.

 

Unless you got a warning, I wouldn’t worry too much. Iconic FJ sells bolt in brackets for coolers that you have to plumb into the stock lines.

 

In 4H. I’m not 100% sure what tranny fluid they used. But they are a reputable shop so I’m assuming they used the right stuff.

 

I will look them up, thanks.

 

Ah you did. Definitely look into that and check out those coolers. Also downshift if it’s hunting. I haven’t hit the high temp myself.

 

Get an Ultragauge or Scangauge so you can monitor the temperature. Even with an external cooler, you can still get above 200 if you're putting extra load on the transmission.

With the gauge, you could have seen the temps rising earlier and downshifted (or even gone into 4Lo). The TC will still be open, but the fluid will be doing less of the work in a lower gear (i.e. building less heat).

 

Could you have used 4L in this situation?

If it works and this isn't a common problem, you could just take is easier going up and not spend the extra coin.

 

Just add a

$78 Derale 13504 Series 8000 Plate and Fin Transmission Oil Cooler , Black

Derale 13504 (or any similarly large cooler)

Should lower those temps by 15-30 degrees. Use Toyota ATF WS and be sure to check the level at the correct temperature after purging all air out of the cooler.
Super easy install.

TBH idk what temp that warning goes off at but I'd consider a drain and fill before you add the cooler. Then a level check after install. I've had mine over 260 and that warning never came up. I assume to get that message your system got very hot and would now benefit from some new fluid.

 

At least for the 2020, the service manual indicates the warning comes on at 302F

 

Soo it’s an idiot light?

Like the low oil pressure light on a lot of modern cars. It’ll let you know after the damage is done…

 

Exactly right. If I started gear hunting on the freeway I’d see my TCT start shooting up quickly on the scangauge.

This will be the time to shift into S4 and let the trans cool down for a bit.

If I’m wheeling, I’d park for a bit, pop the hood and let the engine and trans cool down before continuing.

Temp monitoring is huge for longevity. Depending on your use and region, some additional cooling is certainly an option worth considering.

 

So does driving off road in 4wd keep the trans temps lower? Thank you

 

The warning is for safety (i.e. pull over as soon as possible so you don't lose propulsion in the middle of the road).

@Derf external cooler is not necessary. Just use 4low more often off road. Easy rule of thumb is if you air down, run in 4low. It's better to be in 4low and keep the revs up - the radiator fan spins faster, the water pump spins faster, and the transmission fluid pump spins faster.

 

It isn’t 4WD itself, it’s the lower gearing of 4L that can reduce how hard the transmission is working.

 

I was always told that 4L is for low speed, short distance.

 

Yeah, that makes sense for safety. Although it's damn high I'd be worried that the fluid in the trans is pretty broken down now by the time that warning comes on.

Just re-read OP's post... Definitely shift into 4low next time. I can't imagine you would have overheated in 4low with it being 73 degrees outside.

For reference when I hit >260F it was 120 degrees outside on a "black" level trail which took at least six hours to complete with a big convoy. Every rig was overheating at that point. Texas heat is no joke so most of us added external coolers. I don't think most people are using their rigs in that sort of environment.

Low speed being less than 30mph. Loose surface (ie dirt, mud, rocks.) There is no distance limit on 4low.

Generally speaking keep it off pavement and under 30 mph and 4low is good to go.

 

You’re not the first to think that 4Lo is only for short distances. Maybe there’s a reason where that advice comes from, but I can’t really think of any reason for it.

Like anything I suppose, you should use 4Lo as long as necessary as the conditions require.

To me, a long, slow, uphill slog on a loaded 4runner with upsized tires is the perfect condition to use 4Lo to maintain cool transmission temps. Same goes if it was downhill, to keep brakes cool.

 

Good advice here.
I would do the drain&fill procedure and make sure to use Toyota WS fluid.
Then monitor the two transmission temperatures with a scan gauge. Or get a Carista dongle for the OBDII port and monitor it with a cell phone app like “Car Scanner OBD2” for iPhone. Get a baseline for your normal operating temperature and keep an eye on it while 4Wheeling.

 

You were given wrong information. There is no added harm to any of the vehicle components in 4low vs. 4hi. There's no limit on duration; it's not uncommon to keep in 4low for a week on longer wheeling trips.

You overheated due to low airflow through the radiator (which is also the ATF cooler), combination of low vehicle speed and low engine rpm, so the fan was spinning slowly. Upping the rpm in 4low increases the fan speed.

 

the fan speed makes sense.

 

The breaks did get hot as well. Going to add power stop bug brake kit this fall.

 

^That's the other benefit of 4low, vastly more effective engine braking, so you aren't riding the brakes (and transferring more weight to front wheels) on steep descents.

 

Install scangauge to monitor trans and tconvert temps
Install trans cooler
Put into 4Lo
*I manual shift and use engine breaking