This is my first summer with this 4Runnner. 2002 Limited, 2WD, factory everything (no mods). Got a bluetooth ODBII reader and the Torque app for Android and I'm seeing temps of the transmission peaking between 205-F and 215-F in stop-and-go driving (about 198-F on the highway) while the engine coolant temperatures are pegged at 199.5-F.

Time for a transmission cooler?

How long have you been monitoring temps? Trans temps can swing wildly, and believe it or not, stop and go driving, and low speed driving, leads to the highest temps except for climbing grades. The reason being is the torque converter is unlocked, which causes the fluid to heat up inside it. Once at speeds above 50MPH when the torque converter locks up again on flat ground you should be seeing temps drop down into the ~160-170F range though.

BTW, your coolant temps might also be a bit on the high side. Normal is more in the 185-190 range.

EDIT: just noticed you're in Phoenix and seeing 100F+ heat...that might account for the high temps too...

If you haven't done any maintenance on the truck, it might not be a bad idea to refresh the trans fluid, coolant, and make sure your thermostat is oriented correctly with the jiggle valve at 6 oclock. You may also want to check your cooling fan clutch for proper operation.

Forum contributor Timmy has videos that cover all that and more. YouTube

Couple things:

If you are regularly seeing 200*F temps for coolant, your thermostat is upside down. It should sit right around 190*F +/-3*F or so.

Trans temps with the stock cooler setup are generally around 100*F above ambient, a little warmer when the AC is on. Expect a ~20*F jump above that when the torque converter is unlocked (most of the time around town).

Those numbers sound normal for Phoenix in the early summer. I would expect you'll see trans temps over 200*F for most of the hot weather months. Its up to you if you want to cool it more (it did make it 17 years fine so far... so...). Keep up on the regular trans fluid changes (drain and fill every 15k-30k miles with quality fluid).

Of course, everyone else on here will tell you your transmission is about to blow up as soon as you see 200*F.

-Charlie

Good questions, I was a little light on the details.

I've only been watching temps for a couple weeks. Prior to Phoenix being 105+ I was 5-10 degrees cooler with the transmission. Engine coolant temps are always the same once warmed up.

I have only done a drain and fill of the oil and transmission (not a flush of the trans. I wanted to see if I'd see slipping after a change and just eject this T4R and get another rather than replace the trans.) I have not flushed the coolant. Looks like a flush, thermostat check/replace, and cooling fan op are my next 'to do list' items.

Thank you for the detailed reply and excellent advice!


Thank you Charlie, I agree that I'm running hot for the coolant, I'm going to do a system flush and see if that doesn't get both temps down. Thanks for the note about trans temps being generally 100-F above ambient, I've been looking for that kind of info!

For reference if this helps:
I have a transmission cooler. I'm in Georgia and just completed a trip pulling my 1850 lb camper trailer. overdrive off. Midday outside temperatures of about 94. Transmission temps averaged 195 on the open highway at 60 mph. About the same as my radiator temperature. Stop and go through towns saw it peak a few times to 218 but quickly back to lower temps when up to speed again. As I said, was pulling a trailer of about 1800 lbs. Without the trailer am running just a little cooler and my overdrive on.

All that said, this isn't a "don't drive your car!" situation. Those temps are not overly alarming. A bit higher than ideal, perhaps, but not a sign of impending doom.

When I got my 4Runner I put my ScanGauge in and saw my coolant temps were regularly 195-205+. When I replaced the thermostat and found it upside down, I also noticed it was dated 2007 manufacture. So it's quite likely my 4Runner had been running those temps for over 10 years and ~100k miles with no issues. As you know, at those temps, the coolant temp gauge is still reading normal because it's heavily buffered.

So, just a sign of some recommended maintenance and steps you can take to ensure you're giving it the best chance of lasting a bunch more miles.

Use and OE thermostat and make sure the jiggle valve is at 6 o'clock when installed (upside down from most all other engines). OEM coolant is best, but there are plenty of other options. Since you don't see temps much below freezing, I would suggest running ~60% water / ~40% coolant for better heat transfer from the engine. If you do go mountains (below maybe 10*F), run 50/50 like normal.

You should never need to do a flush of the trans. Just a regular (ish) drain and refills. If it has a questionable service life before you got it, do a few drain/refills spaced out over a few oil changes.

-Charlie

Sorry for the delay, busy month with lots of heat and driving.

I did a THOROUGH coolant system flush on 7/13/2019 (drain current coolant//fill w.distilled water//drive for 20 minutes//thoroughly drain//refill... three times, then filled up with Valvoline pre-mix Toyota-spec Red (burped it, removed, cleaned, and properly filled the overflow tank). The Toyota OEM stuff is going for $32-gal (concentrate) which is absurd.

I then promptly drove a 650-mile round trip, followed by 250-mile round trip. Temperatures seem to be lower but not by a large margin like I was hoping. Seems the coolant that the PO had in there, despite being yello-green Ethylene glycol was doing a decent job.

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I'm using TORQUE for Android and a bluetooth ODBII module** to constantly monitor temps of the engine coolant and the transmission temperatures. Here is what I am seeing now:

Ambient temps here in Arizona are 100-116-degrees daytime. Its the summer.

Coolant temps are pretty static, between 195.8 and 199.6, averaging 197.6.

Transmission temps (after engine warmup) range from 176.0 to 226.4, averaging between 198 and 219. Still way too high in my opinion.

I do note that the vehicle being in Overdrive, unless at a constant highway speed on flat surfaces, makes the transmission work harder. I am making an effort to remember turn it off when I am driving around town. Transmission temps stay lower. Also, sitting at stop lights and in traffic is a killer. In the time it takes for a stop light to change the transmission temperature can fluctuate as much as 15-degrees.

I think I'm going to add a transmission cooler. Suggestions?







** I'm using the BAFX Products BAFX3127 ( Amazon: https://www.amazon.com/gp/product/B005NLQAHS ) this is the best ODBII reader I've owned out of the half dozen I've gone through. Recommended by Timmy the Toolman on one of his vids. Thanks man!

Being out in AZ I would opt for either the Tru Cool 4589 or Hayden 678.

98 degrees and 30mph driving behind a combine for 10 miles and then city driving my trans pan temp was 151f. It’s a 32 mile drive. I have an aux cooler I snagged at the junkyard. It’s not as big as the truecool. You put the truecool on and it should be good to go. The puppy hauler has that 4589 bypassing the rad and it does great.

The 97 Limited Puppy Hauler thread has the install. It’s big you will need to space out the horn some.


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Thanks fellas. @19963.4lsr5 I found your post here, thanks!
https://www.toyota-4runner.org/1851716-post31.html

Ordered. $75.50 on Ebay. ($12 less than Amazon)

I know what I'm doing this coming weekend!

Keep us up to date with your temps.

Also make sure your fan clutch is up to snuff as well to move enough air over the radiator, condenser, and soon to be cooler.

Will do, thanks!

I'm debating doing the transmission filter at the same time. I did a simple trans drain and fill about a month ago. The fluid smelled burnt but wasn't black and I did not have too much particulate matter in the drained fluid. Just thinking about this being a "while I'm under the car, may as well..." kind of thing.

Think of it as more of a strainer than a mesh filter. I’d drop the pan more to see what material the magnets are holding. But if you do drop the pan, then by all means change it.

I’d also consider one of these while installing the cooler. It keeps all the unwanted gunk out of the valve body. I personally can recommend them again now that they have gone back to an aluminum housing:
http://https://www.magnefinefilters....8M-3810000.htm