I noticed that my T4R was running hot, at idle, yesterday. Coolant Temp approx 205 deg F and Trans Temp Spiked to 210 deg F. While driving coolant temp 190-193 degF and trans temp 180 ish degF.
Checked coolant and needed to add about a quart or a little better, reservoir was empty so topped it off. This morning after arriving at work the reservoir seems to have lost about 1 1/2" of coolant.
No puddles and no milkshake (if I am understanding "milkshake" correctly) signs that I saw.
I did notice that there seems to be signs of coolant at the bottom drivers side of radiator. I seem to remember that being discussed before.
With the long weekend approaching I am contemplating just replacing the Rad, Trans fluid ( I have not checked it yet....got home way late from work last night) and adding a trans cooler.
I can get a Denso Rad from Napa locally or a Spectra from AZone locally today as well as a hayden cooler locally.
Thoughts from those with more experience than me.
Thanks in advance.

You have a pretty good size leak if you're loosing that much coolant in a day.

A picture of the radiator would help. Is this the original radiator? How many miles on the truck?

From what you have given, I would go ahead and swap out the radiator and put new fluids in your tranny(if you haven't done that recently).

Swap radiator and flush your fluids.
Better safe than sorry.

Couple of things:
- My '06 V8 runs at 203 degF engine temp all the time after warmup, pretty much independent of speed, outside temp, whatever. I don't think your 205 degF coolant temp is out of line.

- As far as the overflow tank level, it fluctuates with engine temp. It will be lowest at cold temps, as the system sucks coolant back into the radiator, and fullest at operating temp, when the coolant expands and pushes out through the overflow tube into the tank. So, it's important to check the tank level under the same conditions every day. Usually in the morning when it's completely cooled down is a good time to get consistent results.

- A transmission cooler certainly won't hurt, although occasional excursions to 215 deg are not much cause for concern. My pan temp runs around 180-190 under normal cruising, and the torque converter fluctuates anywhere from 0 to 15 degrees above that, depending on how much torque converter slipping is going on. I hit 235 in the torque converter and 220 in the pan last week pulling a 2500 lb trailer up an 8 mile 7-8% grade in 70 deg temps. Since that only lasted 10-15 minutes, I wasn't at all worried.

It's also possible that you were more than a reservoirs worth low and when the vehicle cooled it sucked the rest in to the radiator causing it to be low upon next inspection. If there was still coolant in the reservoir the radiator should be full now. Refill to the appropriate hot or cold mark, then check again. If there's a coolant leak, the crystallized pink should be pretty well indicated.

For some more data points, my coolant runs between 185-195 and my trans runs 165-180 at the pan. The only time I saw it get near 200 was on the 3 mile ascent coming south into flagstaff which is about a half mile increase in elevation.

Even if you topped up the radiator and the reservoir, there is still some trapped air that will work its way out of the system during the next few hot/cold cycles, so it's normal to see coolant loss like that after bleeding the system (basically what you are doing). For me it usually levels out after a couple days. If the level continues to drop after that then you have a bigger leak.

The transmission fluid is heated and cooled next to engine coolant in the radiator. So if the engine coolant is running hot, the transmission fluid will run a bit hotter. There is also heat conducted from the engine to the transmission directly, so same thing.

Every automatic transmission I know of runs the transmission fluid through the radiator like that, so an additional external cooler is not always necessary. It is a good idea if you're towing.

Go with the Denso and NOT the spectra. Denso is OE for Toyota.
Don't 4runners come with transmission coolers?

Thanks for the input folks!
My temps were much cooler today than yesterday and the ambient outside temps were about the same.
I realized that I filled the overflow reservoir while the T4R was on an incline ( burping the system) so my guage of the fluid level was not at all accurate....I did mention getting home from work waaayyy late right? Brain fart.
I have noticed some pink crystallized coolant around the drivers bottom of the rad and if I recall correctly from reading on here that that is a common failure/leak point.
At the least I will do a few drain/fills as I am sure it has never been done.
Heck, when I changed the plugs a few months ago the heads still had the 2 different makes of plugs (Denso on one side and ? on the other).

Another question....
Is the Mlkshake issue not really an issue for the for the 4th gens like it is on the 3rd gens ? Most of my searching results in 3rd gen's with the problem.

Thanks again everyone.

Coolant for me in Houston's VERY bipolar weather is between 185-195


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So according to multiple sources including sonax who makes repair/upgrade parts for the Toyota transmissions, 215° is way too hot for the transmission to be operating at on a regular basis. Ideally you want the temperature to be below 180.

Between 150° – 160° is where you ideally want it to be. At 215 degrees you'd want to be changing that atf out every 20-25 at the most to make sure the fluid can do its job correctly.

Mine runs at around 180 most of the time in 90 degree temps while moving at low speeds. On the highway I'm at around 150 or so after about 10 minutes time. Stop and go in the mid 90's puts my torque converter output temps around 195-200. Hard acceleration after stop and go in the same temps, I'm at 210-215 easy. Repeated hard acceleration puts the temps up around 225 or higher.

I have the factory aux trans cooler. 2005 v8. I intend to put a small spal pusher fan in front of my stock aux cooler on a switched relay to combat stop and go scenarios this fall.

I change my fluid every 25k or so. Cheap insurance.

My v6 2004 T4R coolant runs 184f-190f, scanguage2.

Reviving rather than starting a new thread...i got an OBDLink BT scanner and set it up with OBD2 Fusion app today. My 2006 V8 2WD engine temp has apparently been running at 200-210, because that was the reading today after 2 short 4 mile/10 minute drives with the new scanner hooked up. My engine/water temp dash gauge has been steady and consistent since i got it last month...just below half when warmed up, and sticks there (except for the time couple weeks ago when upper (original) radiator neck cracked, coolant gushed out and temp rose up towards but not quite into red/danger zone. I have since replaced radiator and flushed/filled coolant system with about 85% Zerex 50/50 pink and 15% distilled water).

This water temp seems high to me. Today it was 70 degrees, and like i said i've only had it for a month. I live in TX so imagine the temp will go up a bit in the summer? Like i said, the dash gauge normally just sits there at just below halfway, whether it's been 30 degrees or 70.

Curious to see what is does tomorrow on my 25 minute 50/50 city/hwy commute. Today was all city.

Is it possible the Fusion app needs a calibration? I wouldn't think so, as it's pulling it from the ECU.

I have yet to set up trans temp gauge, but looking forward to what that will show.

I had changed my radiator out and was running in the 200-210 F until it fully burped itself. After that .. ~190 - 205 range. (Torque Pro)

I had replaced the 180 degree thermostat, and placed the jiggle valve at 12 o'clock. The OEM Jiggle valve was set at 10 o'clock, within tolerance per the factory manual.

ok, guess i need to do what i thought about doing when i changed radiator...change the thermostat, just to cross that off.

I set up Fusion to show oil temp last night, i'll see what that looks like today.

How are you guys getting transmission temperature readings?