Someone Talk to Me About Pinning the Transmission T-Stat

I have pinned mine on a 5 hour drive and it stayed 10-15 degrees cooler.

 

Which AT temp was cooler? AT1 or AT2.
AT2 temperature is wired to a warning light.
Pinning thermostat may not affect AT2 temperature whatsoever.

 

What was it again? 1 is pan & 2 is converter??

 

Valve Body

 

I pinned mine this june using a cotter pin. Highest my trans got was 185F, thats bombing across texas interstate for hours in 105 degree heat.

my trans used to get +200F
It usually stayed around 168-175F all summer.

To answer your question, Pin in hot months, unpin in cold months

 

What size cotter did you use?

 

I got an assorted set so i just kept trying pins until one fit. Im not sure which size it was, sorry. I can check if you want me to

 

No worries man. Just thought I'd ask in case you knew off hand.

 

I used a 1.6mm dia. stainless R-pin, been in there for more than two years:

 

I have my T=Stat pinned and added an external trans oil cooler.
See: below forums for encyclopedic discussions on trans oil cooling and 'why' s.

TRANSMISSION . Transmission coolers for all Toyotas ... Write up with many pictures

3rd gen Transmission Cooler Upgrade

Added new Hayden from that port to the top of the 678. Then reattached the Lower line from the Hayden to that detached original return line. Based on the strength of GPsevenSixx post # 103 below.

I added a

$53 Hayden Automotive 678 Universal Rapid-Cool 9.5” x 11” Add-On Transmission Cooler – Not for Direct Replacement of the OE Cooler

Trans oil Cooler to my 2021 TRD Sport.

I mounted it in front of the Radiator/AC Condenser cooler. It sits about 3” in front of those 2 coolers and about 3” behind the front grill. Big front nose on that truck - lots of room.

It is mounted on the drivers side as high up and to the right as (you face the truck from the front) much as possible , away from the front radar grill gizmo as comfortable, to keep it in the direct ram air inflow as I could. Moved horns to pass side.

I removed the original Bottom return hose from the radiator trans oil cooler and routed some

$21 Hayden Automotive 106 Transmission Oil Cooler Hose 3/8-IN Diameter x 4.5-FT Length

trans hose from that port to the TOP inlet of the Hayden 678. Based on info from Hayden - a post, from Hayden reply:
From GPsevinSixx post # 103
.

Bottom return line from the Hayden External Cooler to original radiator return line connected with 3/8” id brass double barbed joiner. See below pic.. Obviously, kept the original hose connected to the tubing under the car, Didn’t touch that.



Hayden 678 Rapid – Cool cooler unit, with Hayden 106 hoses 3/8”, Fuel injection hose clamps from Harbor Freight. Hillman ¾”w/1/8”t/3’L aluminum stock for my homemade mounting braces. Misc warpy and external tooth lock washers, bolts and nuts with plastic inserts for locking. Black paint. Vise and hammer for persuading purposes.

Hoses covered in places with larger cooler hose for protection when threaded thru radiator wall and behind, where there is possible contact with other hoses. Paid attention to not KINK the hose at any spot. More than 4-5 in radius bend in rubber cooler lines for me. I blew through the whole set up, cooler and extra tubing, before final hook up to test resistance. Hardly anything felt.

PINNED the T-Stat. Added a quart of WS tested for leaks.

Entered in Oil temp Mode via great post of Post #517

https://www.tacomaworld.com/threads...smission-fluid-level-check-diy.547455/page-26

T-Stat PINNED, check bolt loosened-drained to a ‘dribble’. Maybe 10 oz came out. Additional oil of maybe 2/3 qt needed for the extra hoses and cooler. So, Trans fluid level/amount is accurate.

See below results with me in the PU with about 400 lbs of gear last month. T-Stat kept PINNED.

.

Its 95*F outside, Coolant is 190*F going 65 mph, with Trans oil temps are about 160*F. I can add 10*F by occluding the Hayden with a cardboard blocker and will do so for winter.

Done 5,000 miles ago . No troubles. Above results typical. In winter, I will put cardboard in front of about ½ the cooler and it seems to add 10* F.

I live in SE Arizona. We had 110 days of above 100*F this summer of 2024. Up to Grand Canyon, down to Puerto Penasco, Mexico: Some towing about 1500 lbs and some not. You can understand my concern about oil temps

Per post from Dbarffish at post # 449. If running through the radiator, when the trans fluid is cooler than the antifreeze, I’m sure the trans oil does get warmed up some. But look at the operating results shown above with trans oil routed through the Hayden.

Its is nice to have available, the extra cooling potential, when needed.

Looking at the results, I probably could have gotten along with a Hayden 677 considering my driving habits and lifestyle. Because of my cooler mounting location/method, I could keep the same hoses/lengths and just make another mounting brace and swap it out.

 

Look at the below screen prints. This is with a pinned T-Stat and an additional

$53 Hayden 678 Universal Rapid-Cool 9.5” x 11” Add-On Transmission Cooler – Not for Direct Replacement of the OE Cooler

Hayden 678 Trans oil cooler.
Expressway driving, on the flat, with about 600 lbs in the truck including me. Camping trip.

 

FYI The below is why.
If you off-road or tow, in the desert or in the mountains, you think of extending your trans life. Temps get high quickly with the above activities. You adjust your equipment to meet your perceived needs.