3rd gen Transmission Cooler Upgrade

This mod has been awesome for me. Brings down temps super quick. Total game changer and peace of mind.

 

Just seen this also

 

The fan is no doubt a welcome accessory when stuck in stop-and-go slow traffic, especially if towing.

 

According to Hayden, tube and fin style coolers are 33% less efficient than plate and fin. Better believe you're gonna need a fan with that kit or its not doing much.

 

For those of you who have done the cooler in series with the stock in radiator one can you tell me which line is the outlet (cooled fluid) from the radiator? I could go ahead and figure it out by getting the truck hot then feeling them but I figured I'd ask here first. Truck is a 2022 SR5 4WD.

 

OBD Fusion tells me my trans temp #1 is 187.5 degrees.
This is fully warmed up and idling in 100+ ambient air temps.
I do not have an auxiliary cooler in series with the return line.

Engine hot coolant enters the radiator at the top, and exits through the bottom.
The transmission coolant tank is located in the bottom of the radiator.
This tells me it should be exposed to the lowest temperature coolant in the radiator.

ATF is not sent to the radiator coolant tank until the trans thermostat opens.
My trans thermostat is not pinned, meaning it opens at approximately 187 degrees.
Even if the ATF fluid returning from the auxiliary cooler is much colder, the unpinned trans thermostat will keep the trans ATF at a minimum of 187 degrees.

The next diagnostic step would be taking the un-pinned reading as above, then pinning the thermostat open and letting the trans pan temperature settle.
I will do this on my rig which does not yet have an auxiliary cooler in addition to the radiator coolant tank.
This will give a pinned/unpinned baseline.
This last step is the unpinned temp with the auxiliary cooler in place.

 

So with this theory just adding a cooler with out towing or heavy use could just be a waste of money?

 

I feel that in a perfect world, yes. However, when you're pulling long hills or otherwise taxing the trans then even when the trans t-stat opens you won't be getting down to a "comfortable" temp. The diagram for my Derale cooler shows to put it after the stock cooler so it will cool it further.

 

Not a waste of money... any additional cooling is always worthwhile.

If heavy towing is raising the ATF temp, the thermostat will still open at 187 degrees.
ATF temp returning through the auxiliary cooler will still be cooler than that coming from the radiator tank alone.

If the aux cooler has a fan, that will further cool the ATF on its way back to the trans pan.
There is no downside to having additional cooling in a hot working environment.

 

Yes and no. Even when not towing you can see 200+ deg temps in hot climates. An additional cooler can help keep them closer to that 187 deg. Maybe not consistently lower temps, but when they start to rise, they will rise slower and recover faster.

I could be wrong, but I would think it wouldn't matter where it's placed. Spitball numbers, but if the OEM cooler efficiency is 10%, and the aux cooler is 30%, you're still getting 40% total by the end.

(placed after OEM cooler) 200 deg - 10% OEM cooler = 180 deg - 30% aux cooler = 126 deg final

(placed before OEM cooler) 200 deg - 30% Aux cooler = 140 deg - 10% OEM cooler = 126 deg final


Regardless, if you don't pin your tstat you will always see at least 187 deg pan temp.

At 85 deg outside and not pinned tstat, mine stayed around 195 while towing my ~1600lb trailer, and I saw around 204 while climbing a 6% grade for 3 miles. Before adding an aux cooler I would see ~200 while towing, and 210+ on that same 6% grade. My next trip I'm going to pin the tstat open, but it wont be the same route and far more steep grades.

 

There's too many factors to give a yes or no answer. It depends a lot on how hard you drive and where you drive. For example I had my trans drop a gear and fire an overheat alarm because I was trying to do 70 up a steep hill on 395 outside Mammoth. Is that my problem? Sure. Would I like to be able to do that? Also sure. I also off-road a lot incl. rock crawling and I'd like to be able to think about the transmission temps as little as humanly possible.

Running it in-line with the radiator is a 1 hour install and gives me plenty of peace of mind.

 

@guaco.supreme not sure, I just figured it's best to follow the manufacturers diagram since they hopefully know more than me. LOL! Outside of percentages I suppose if the external is cooler is put before the rad cooler it could cool it to below the rad temp the the rad would effectively heat it back up. Not sure how likely that is though.

 

Before radiator I can see that happening. On trucks that have a OEM trans cooler I don't know that placement before or after THAT cooler matters, I think as long as its after the radiator you're good.

 

Absolutely. I never even considered an external factory one in the equation.

 

Regarding this question, it's been asked a few times in a few different threads, but no one has really been able to give a solid answer. What we find in diagrams conflicts with what people fine when feeling the lines.

The diagram for my truck with aux cooler shows that fluid flows from trans to rad, from rad to aux cooler, then back to trans. When following my lines the upper line on my rad comes from the trans, and the lower line goes to the aux cooler. I would assume trucks without the aux cooler use the same rad, however @Breakdown mentioned in another thread that his appeared to be opposite, and fluid was flowing from trans to the bottom rad port, and the top was the return.

So... in the name of science I'm going to see if I can squash this bug either tonight or this weekend and check mine since my skid plate and such is off right now. I'll report back with what I find.

 

I disconnected my rubber hoses to the hard lines under the radiator. Turned on the truck and the hard line that led into the bottom of the radiator was the line throwing fluid - this makes me believe it flows from the bottom to the top. I have also installed an aftermarket cooler and have yet to see temps above 205 while climbing. Im on 40s. Let me know what you find.

 

@Breakdown thank you for this info, it's exactly what I was wondering. You saved me the trouble of doing the same thing as you just did.

@guaco.supreme I'm interested to see what you find.

 

Thank you all. I bought a small Hayden cooler for my 2021 and was going to install it soon which led me to ask. Sometimes we over think shit

 

Fluid routing from Guac at # post 415 seems accurate.

I have a 2021Tacoma Sport, v6, 6sp, short bed.

Trans oil connections are on the driver side, in the radiator, and the TOP Trans oil hose was noticeably ALWAYS hotter than the BOTTOM hose at the radiator

Why would the TOP hose be the return hose if it has the hotter oil returning to the transmission?
I was concerned about the lack of an additional external oil cooler. In 2023, SE Arizona had 89 days of above 100F temps

I mounted the

$52 Hayden Automotive 678 Universal Rapid-Cool 9.5” x 11” Add-On Transmission Cooler – Not for Direct Replacement of the OE Cooler

Hayden 678, using the Hayden hose, from the radiator/trans oil BOTTOM port to the top connection inlet of the Hayden then spliced with a 3/8" double barbed brass connector, the bottom outlet into the original line (bottom hose) back to the trans.

-- Radiator bottom port to Hayden top inlet;
-- Hayden bottom outlet to brass barbed connector to original bottom return line to trans

I have great results with pinned THERMOSTAT.

May 5, 2024 -1hr 50 min, 111 miles, Engine coolant 198F, PAN 158F, TC 158F, Outside ambient 86F, Speed 53 mph.

June this year at Grand Canyon=4 hours driving, 250 miles, Engine coolant 190F, Pan 142F, TC 143F at 66 mph, Ambient outside temp 42F.
When sitting parked, TC increases 10 F above Pan temp.

July 12,2024 - 6 miles, 13 minutes driving, Engine coolant 198F, PAN 155F, TC 167F sitting at stop light left turn lane, Outside temp 107 F.

TC temps will be appx equal to PAN when driving and rise when sitting.

Seems a pinned thermostat, with an external cooler works well in the desert environs.
Have many other trips with similar results.

Its about 100F outside. Engine at operating temp. Freeway driving. Look at TF1 Pan and TF 2 Conv temps. Waiting at a light, TF2 can get 10F hotter.

 

Why go off feel for making a determination of which line is which when you can disconnect both and see which one is the high pressure line?