Toyota Tundra Forums banner
1 - 6 of 6 Posts

· Registered
32 Posts
Discussion Starter · #1 ·
So yes I am OCD and I own scanguage that reads transmission temp.
It appears that tranny temp likes to stay around 200F even with 75F outside. Of course seeign 210F on my scanguage for first time I went into WTF mode.
So here are some findings
1. Some retard designed external transmission cooler in the place where there is no airflow unless truck is moving. Air actually goes around the tranny cooler while truck is idling (confirmed by cigarette smoke).
2. Most likely the same retard decided to put thermostat that does not send tranny fluid to external cooler, unless temp reaches ...... drum roll here..... 200F. Yes that's right that stupid things does not open until 200F :td:
3. Radiator internal cooler for tranny fluid must be complete crap because it can not keep up with (non towing, regular driving)

WTF Toyota.
So now I have to figure out how to relocate that external cooler somewhere with airflow, and I am thinking about disabling thermostat permanently. Any ideas why not to do this.?

I own 2007 Tacoma and my tranny does not reach 200F when I am towing backhoe behind it. Not sure what the hell somebody was thinking when they designed new Tundra Sequoia towing package system.
Now I live in New England so anybody south of me is probably running transmission hot. You may want to check your fluid.
I did check mine and it is discolored despite the fact I told Toyota to replace it 300 miles ago. I am guessing service F me and they just charged me for replacement and did nothing. There is not even a wet spot on transmission oil pan so they either miracle mechanics or just flat out liars.

· Registered
32 Posts
Discussion Starter · #2 ·
I am goign to park this info here from Tundra thread
I thought I might share a mod I have done to my '08 Tundra 4.7, adding an auto transmission oil cooler radiator to our non OEM tow package vehicle, bringing the towing capacity to max available for the Tundra.
When we purchased our Tundra 2nd hand, it did not have a tow hitch, so it also did not come with the transmission oil cooler. We had the dealer add a tow hitch as part of our purchase package, but to add the oil cooling was way too expensive. Without the transmission oil cooling though, recommended towing capacity of the Tundra is about 70% of full capacity when OEM towing package is installed.
So I did a bit of research and worked out that it really is not that difficult to fit an oil cooler. If you've done a bit of mechanical work on your truck, this should be pretty easy for you.

The parts you need are mostly OEM parts and can be purchased quite reasonable from Toyota Parts Zone.
The radiator I bought is a non OEM, as it is way cheaper, I bought mine from Makco Transmission Parts, a Derale Series 8000 cooler.
OK, here are the OEM parts you need to buy in order to cool the transmission oil.
- Transmission Oil Thermostat, part # 32971-34020 "A" in attached drawing
- O Ring, x2, part # 90301-19020 "D" in attached drawing
- Oil Cooler Tube assembly, part # 32910-0C010 "C" in attached drawing
- 3/8" hydraulic flexible hose
- clamps to suit 3/8" hose

Now, the oil cooler tube assembly is not really important, but I got it to make sure that all is neat next to the engine block and to try and keep it as close as possible to OEM standards.

You will need to remove the existing Transmission Oil Cooler assembly from the passenger side of the gearbox, accessed from under the truck. This is quite straight forward, I think you need to remove 4x bolts, the heater hoses and oil cooler hose, refer to attached drawing.
Be aware that water from the engine radiator/heater as well as about a pint of transmission oil will flow out when you remove the assembly and hoses.
Completely remove the transmission oil cooler assembly and proceed to disassemble it, by removing the Transmission Oil Cooler Spacer, "B" in attached drawing, held on by 3x bolts, also take out the 2x O rings and discard them, again, refer to attached drawing.
Now, install the two new O rings, then assemble the Transmission Oil Thermostat you bought, to the Transmission Oil Cooler. You will see a removable pin on the Thermostat, DO NOT remove that was yet!
Re-install the complete Transmission Oil Cooler assembly to the side of the gearbox.
If you have bought the Oil Cooler Tube assembly, bolt that to the passenger side engine block, this takes a bit of maneuvering to get it into place.
Now, cut 2 pieces of suitable length of your 3/8" hydraulic hose and attach one end to the new Transmission Oil Thermostat and the other ends to the Oil Cooler Tube.
Cut another 2 pieces of suitably long 3/8" hydraulic hose, attach one end to the Oil Cooler Tube assembly and suitably route the two hoses so they come out the passenger side in front of the engine radiator, see attached photo.
Install the transmission radiator you bought, see photo, and attach the two hydraulic hoses, one to the top and one to the bottom of the radiator, again see attached photo.
A side note, there are arrows marked on the Transmission Oil Thermostat, indicating which connection is in-flow and which is out-flow, so make sure you note that when connecting the hoses to the transmission radiator!
You will need to add about a pint and a half of transmission oil back to the gearbox, the extra half pint is for the hoses and radiator, and top up your engine radiator water.
Thats pretty much it for the installation, of course, each hose connection requires a suitable 3/8" hose clamp.
Start engine and allow to get to operating temperature.
Now, back to that removable pin on the Thermostat you installed. Once the engine is up to operating temperature, remove the pin. What this pin does is its keeping the valve open to allow transmission oil to flow to the newly installed radiator and for one of the better words, priming the whole oil cooling system. By removing it, the valve actually closes and prevents oil from circulating through the radiator until the oil gets warm enough to require cooling, usually only when towing.
Thats it, you're done. Your Tundra now has the full OEM towing package and you can now tow to full capacity!

I did go to the next step and wanted to keep an eye on the oil temperature whilst towing. I thought about buying an aftermarket transmission oil temp gauge, but I really did not want to add a gauge if I can get away with it. If you like the idea of extra gauges, then thats a good option. If you do go this way, you will either need to buy a mechanical oil gauge, or and electrical one with a suitable electrical sender.

Again I did some research and found that Toyota have mostly pre wired for most OEM add ons/extras and worked out that the wiring harness is already wired for the OEM transmission oil temp gauge located under the tacho. However, since our truck was not fitted with the OEM tow package, that gauge was not present.
So I started looking around for a used dash with that oil temp gauge fitted under the tacho. I found one on eBay and bought it. I installed the 'new' dash and voila! works..'plug and play', no extra wiring required!

Hope this DIY will come in handy with those who bought a Tundra without the OEM tow package.

· Preferred Dealer
1,171 Posts
Toyota wants it to run at 200 for better mileage. It acheives this through the transmission warmer, which is located on the side of the transmission, and uses coolant. Under light load and low speed, the warmer also functions as a cooler (as cool as the coolant will alow)... However, under high loads and low speeds, the warmer works a little too well, and likely exacerbates the hot fluid issue... so it's a catch 22 if you'd like to remove it. Obviously, your Tacoma doesn't have the warmer., but does have the lower radiator tank cooler. I'm am not sure at what temperture the t-stat opens, I'll try to dig that up for you. The front mount ATF cooler is very effective while moving. It is mounted off to the side so as not to add heat to the air in front of radiator. In 2010/11 Toyota moved the cooler in front of the radiator so the fan can its job at slower speeds. Adding an electric fan to the stock cooler has long been a back burner project of mine, which would solve the low speed high load issue. There is no cooler in lower radiator tank.... that would also solve the issue slow speed issue. LMK if you have any more Qs?.

· Registered
146 Posts
I just installed a scan gauge on my '08 5.7 Tundra with the tow pkg for the purpose of keeping a close eye on trans temps and actual coolant temps. Driving around town trans temps are running 188º to 200º with the air temp at 81º. Stop and go light traffic. I was surprised to see the temp so high. "Would like to know what Toyota says MAX trans temps can be expected." Coolant temps stayed around 195º. Here in Texas the oa temp will reach 100+ very soon. We pull a 9K # 5th wheel RV, wonder what those trans temps will be while towing that load. Been towing for 5 yrs now, have had the trans fluid changed twice in 73K miles on the clock.

· Registered
316 Posts
Who says 200f is too high for todays very high end ATF? Its not. Not even close.

Most of ATF temp charts you find online right now do not apply to most current ATF, do not be fooled.

Toyota knows what they are doing. We hear of very few transmission issues on Tundra forums compared to any other big truck forum out there. Our transmissions are damn good, let the thing work as designed.
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.