Transmission cooler - fan needed?

So I've had the transmission temp light go on a few times now, I'm assuming because I'm rolling on 33s vs the stock 29 tires plus offroad bumpers and fully loaded truck (04 Nissan Xterra), decided to get a transmission cooler.

Seems like most of the tranny coolers are just passive heat sinks (ex: B&M SuperCooler 70266), however some of the more expensive ones come with an electric fan (ex: B&M Hi-Tek SuperCoolers 70298). The latter are way more expensive, and I'm wondering if I can get away with a basic non-fan one for general off-roading? The times the light came on was during long steep (and slow) hill climbs, I tried shifting into 4Low but the temp spike still keeps happening. In this situation, I'm guessing there isn't much airflow happening, so I'm assuming simply passive cooling via the ambient air temp might not be enough and I need a fan on my cooler?

To qualify, I live in BC Canada, so the temps are usually around 86F, rarely get above 95F, so it's not like I'm wheeling in Texas!
 

MANUCHAO

Aventurero
The latter are way more expensive, and I'm wondering if I can get away with a basic non-fan one for general off-roading? In this situation, I'm guessing there isn't much airflow happening, so I'm assuming simply passive cooling via the ambient air temp might not be enough and I need a fan on my cooler?

Maybe...
&
Yes...
If you are experiencing over heating mainly during low speed climbs a fan should be used.... i would get the biggest cooler (think bigger surface area better heat dissipation) that you can fit.... in front of rad?
 

rayra

Expedition Leader
If you vehicle doesn't already have an electric fan it might benefit from a pusher-style in front of the radiators. Depends on where your trans cooler is mounted, what sort of room you have in the stack / behind the grille.
And if you do a lot of slow-crawling it might be a good idea anyway.
 

vwhammer

Adventurer
I feel like all the things you listed are exactly the reason auto transmissions get wrecked in off roaders.
Tall tires, big bumpers, loaded out truck and slow speed with higher revs all equates to hotter trans temps.
This can only get worse if you did not change gearing with the larger tires.

I would also suggest using 4-low more often.
This takes a considerable amount of strain off of the torque converter to help keep fluid temps in check.

I generally like to run the biggest trans cooler that I can fit with a thermostatically controlled fan.
The only real issue here is that, even if you try to pick out some cheaper parts, by the time you get all the necessary bits to make it all function the way it should it's still not that cheap.

What parts do you need?
Well here's a rundown on what I like to have:
Big trans cooler with fan
These units on ebay are of pretty good build quality for the money and come with a fan.
The price isn't bad either.
https://www.ebay.com/itm/30-Row-10A...256288&hash=item3d2ef59de5:g:3ycAAOSwnJtb4VQt

Temp controlled bypass
Ideally you don't want you trans fluid being cooled until it is at least up to operating temp.
This bypass does just that. It installs before the cooler and opens a loop bypassing the cooler until the fluid is at operating temp.
https://www.ebay.com/itm/Derale-Tra...714739&hash=item51efce848c:g:TdAAAOSwlMdc3C50
(you can usually find these a fair bit cheaper. this was just the first one I came across on ebay for reference)

Thermo switch for the fan
Obviously this controls at what temp the fan comes on.
These can be as cheap or as expensive as you are comfortable with.
Naturally some are more reliable than others.
They make adjustable ones and fixed temp units and there are various mounting arrangements.
I sprang for some pricier units housed in some -10 an fittings so I could eliminate a couple of clamped joints in my system.

Dual remote trans filters
I am of the opinion that the more fluid the better.
Why not ad a bunch of capacity with a couple of big remote mounted trans fluid filters.
More fluid takes longer to heat up and wear out.
Not to mention the obvious but you also get a substantial amount more filtering capability over the stock trans filter.
I like these units from Derale.
https://www.ebay.com/itm/Derale-Eng...037225&hash=item51d8f13b4c:g:j4cAAOSwrWRc3C5~

Pretty standard rubber line with good clamps
For cost reasons I just roll with some properly rated rubber line and oetiker clamps that take the special pliers to close up.
I make sure I get the 360 degree clamps for more consistent clamping
you could do AN stuff if you really wanted to but for the price of two or three AN fittings and the line you can have a butt load of clamps of various sizes, another butt load of some plain ol' pipe threaded, barbed fittings in various sizes and the pliers to clamp them.
I also like using relatively standard stuff for the fact that if something goes wrong somewhere in the system you can generally get the stuff you need at any parts store to get it fixed or bypass something in order to get home.

My only caution would be to keep your line runs as short as you can to avoid any serious pressure drop across the entire system.
I have never experienced any issues with this but it is theoretically possible so just keep it in mind.

Beyond all of that complication, running two oil coolers is also a good idea as has been mentioned.

I should also mention that maybe you should give the truck a good once over to verify that it is not another issue that might be causing the trans to overheat.
it could be something as simple as the oil coolers location.
Is it safe to assume that the engine is not getting too hot.
Maybe the rad fan is not working and, if the stock trans cooler is the loop inside the radiator type set up, it could be causing the trans to warm up.
Could be an actual issue with the trans.
Do you notice any other trans related issues on the street or on any other occasion?

Just my thoughts on the topic.
 
Thanks for the detailed reply guys!

Yeah, looks like it's going to be a bit expensive, but definitely worth it - especially considering the heavier vehicle weight, as you say @vwhammer

In terms of other potential causes for the A/T temp overheat:
  • I did a body lift recently, which meant the radiator was offset from the rad fan. However; I actually took care to relocate the radiator down using a bracket to ensure it stays in-line with the engine and fan! So I doubt that's the problem
  • The engine is not running hot - fresh radiator fluid and clean rad everything seems to be fine in that regard

I don't notice any issues with the tranny during regular road or highway driving. The only tiny thing is that it sometimes doesn't shift ideally because of the bigger tires and stock gear ratio I'm assuming

I do try to ensure I'm in 4Low when going up anything steep or off-road, for sure. But I did still get the A/T light when in 4Low and in 2nd or even 1st gear...
 

Wilbah

Adventurer
I know little about this subject from a scientific perspective and it seems you've gotten some good advice here- I had a thought- as you have the fan/radiator in place appropriately- is your fan (the regular engine fan) on an electric clutch or just mechanical? Meaning is it always on if the engine is on or does it only come on when the engine is at a certain temp? Could a temp difference between when the coolant needs to be cooled by the fan versus when the AT fluid needs to be cooled be the "disconnect" in the systems? Meaning that the engine is "telling" the fan everything is fine, but the tranny needs cooling. Not sure a mechanical fan is preferable as it's always on, always draining engine power. I think some of the other replies would work (I like the extra filters idea for more fluid- like the larger diff covers) and be better than changing the fan style, but I was curious.
 

javajoe79

Fabricator
I know little about this subject from a scientific perspective and it seems you've gotten some good advice here- I had a thought- as you have the fan/radiator in place appropriately- is your fan (the regular engine fan) on an electric clutch or just mechanical? Meaning is it always on if the engine is on or does it only come on when the engine is at a certain temp? Could a temp difference between when the coolant needs to be cooled by the fan versus when the AT fluid needs to be cooled be the "disconnect" in the systems? Meaning that the engine is "telling" the fan everything is fine, but the tranny needs cooling. Not sure a mechanical fan is preferable as it's always on, always draining engine power. I think some of the other replies would work (I like the extra filters idea for more fluid- like the larger diff covers) and be better than changing the fan style, but I was curious.
In his case the stock trans cooler is a heat exchanger within the radiator. Once you're making more transmission heat than it is designed to dissipate, it can slowly get hotter and hotter. That is what is happening here.

Mechanical fans don't always run full blast, some are thermo clutch fans and some are controlled by the ECU. Mechanical fans are almost always better than electric fans in terms of CFM or cooling power if you will.

In this case an external transmission cooler is what is needed. Whether it needs it's own fan or not would require testing the temps of the fluid to find out.
 

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