So the bottom line is..

if we are going to tow, this is going to be an essential upgrade to prolong the life of the vehicle?...thank you in advance for any replies.

Personally I would not think twice about pulling a 2,500 lb trailer across the country and back with the stock setup only adding a brake controller for safety. If I were going to pull a 5K trailer across the country and back several times I would not think twice about trading the 4Runner for a vehicle built for heavier towing lol. The 4Runner is what it is: An extremely versatile vehicle that handles many tasks well and excells at a few like off road performance stock off the lot. As with most multi purpose vehicles it does not do everything well, like pulling heavier loads.

With that said an auxillary transmission cooler would not hurt anything. Would it help? I would not install one based on my opinions above but as I said it won't hurt anything.

With 3000# behind me i can count on 30-40 degrees cooler trans temps with it.

If your trans fluid stays below 175*F when towing, then you do not need an auxiliary trans cooler. And your fluid change interval would be 100,000 miles.

For a rough estimate, every 20*F above the 175, you fluid change interval is reduced by half, running the fluid to 200*F would require a fluid change at 50,000 miles.

Toyota says that under normal driving conditions, your trans fluid change interval is beyond 120,000 miles. If you have bigger tires and stock gearing, this alone will make your trans work harder and will create higher heat levels.

Under severe conditions, towing, offroad, car-top carrier, etc, your trans fluid change interval should be 60,000 miles. This is due to the assumption that your trans will run hotter under these conditions.

Here is a good, easy to understand discussion of trans temps and solutions to overheating. http://www.roscommonequipmentcenter....notes/nn15.pdf

Just for reference, this morning was 60*F and on my way to work on the interstate, I saw trans temps of 130*, without the cooler I was seeing 140* under the same conditions.

There is a concern during cold weather that an auxiliary cooler could over-cool the fluid and your transmission could fail due to loss of lubrication.

As a note, when I installed my cooler, the trans fluid looked a bit brown and was thinner than the new fluid that I put in the cooler. Like I stated earlier, my trans saw 220*F with no trailer going over a local small mountain range (3500 ft elevation gain), that was with 3 adults in the truck. I plan to change/flush my trans at 30,000 miles just to be safe.

If you are considering the cost of the cooler and whether it is worth it for you, a trans flush and refill at the dealer is between $150 - $200 if I remember right from when I had it done on my Tacoma. So the cost of the cooler is less than having to change the fluid early, if you do the work yourself and if you plan to keep the truck long enough to put 100K+ miles on it.

I headed up to the mountains this weekend, no load other than toting the family and gear.

With trans cooler:

I saw 135*F on the freeway in mostly flat ground.

Heading into the mountains, max 175*F pulling 4th gear on a sustained long uphill grade. Mostly running 150-160*F in mountainous terrain, up and downs.

Max 175*F wheeling forest roads going slow with the kid sleeping in the car seat.

Outside temps were cool, 55-75*F, with cooler temps the higher we got in the mountains.

I have noticed that it takes longer to warm the trans up when the truck is cold, trans hovers around 100*F until the engine coolant warms up to 180*F, then the trans stays around 120*F on surface roads at low speeds and low RPMs (1100-1500 rpms) as soon as I get up to freeway speeds or the engine is running around 2000RPMs, the trans warms and stays at 130-135*F.

As discussed in the "towing section", I can tell a big difference in trans temps up steeper grades when the torque converter locks up (4th and 5th gear only). The trans temps are much lower with the torque converter locked, mid 160's vs 180's with it slipping.

Just a little update to give you guys some numbers.

I cant wait to pick one up.. im thinking about getting a long one for more cooling.. i added one on my lexus gs400 after i put a higher stall tq. So it should be a breeze!

I've got a permit for 5 days and 4 nights on the White Rim Trail at Canyonlands - Island-In-The-Sky for next April and May, so we'll be loading up and towing our ~ 3,000 lb A-frame trailer, 4 people, and a mountain of crap from Seattle down to Moab for some red dust, sunshine, hiking and wheeling, and tranny-cooking temps. Recalling that on a cool day last September going over a pass in the Cascade Mountains east of Seattle, we flirted with ATF temp of 235 degrees on the ol' ScanGauge, so I picked up a B&M 70264 cooler. It's somewhat irritating that Toyota touts the 5,000 lb towing capacity, and then conveniently fails to mention that if you're towing a heavy load / towing up a hill / the ambient temp is high - chose 2 of the 3 -you'll overheat the ATF. Anyhow, I need to get off my fat fundament and get the tranny cooler installed, but have a couple of questions/concerns.

1 - The hard lines from/to the tranny are 3/8" OD, but the cooler has 5/16" OD in and out fittings. I got a couple of copper 5/16"-to-3/8" adapters (JEGS Performance Products 15946 JEGS Brass Barbed Hose Connector), and am thinking of using them near the cooler fittings to step the hoses down from 3/8" to 5/16", since I don't really want to use 3/8" hoses on 5/16" fittings or 5/16" hoses on 3/8" hard lines. Agreed that this introduces some additional potential points of failure, but I think I would rather have 6 clamped joints with properly-sized hoses than 2 clamped joints with improperly-sized hoses. Has anyone run into problems using 3/8" hoses on 5/16" fittings? Another concern is that the ID on the 5/16" sides of the adapters is about .025" smaller than the ID of the cooler fittings. I was at home sick the day they talked about both computational and finite-element fluid dynamics, so am wondering if anyone has ideas about (1) the wisdom of skinnying down from 3/8" to 5/16" on the cooler in the first place, and (2) skinnying down the ID's even further if I decide to use the adapters. One would assume that the reduction in ID would force the fluid circulation pump (or whatever it is) to work harder, and speed up the flow but decrease the pressure. Any knowledgeable fluid-flow heads out there with ideas about what to worry about - cavitation, supersonic speeds, Bernoulli and all that? The change in ID's in the adapters is a sharp step rather than a smooth venturi, if that matters. And my wife says that I over-think stuff!

2 - The consensus around here seems to be that the ATF should exit the tranny, go through the standard ATF cooler section at the bottom of the radiator, then through the auxiliary ATF cooler, then back to the tranny. On the tranny, I see the ATF outlet and inlet fittings and hard lines but it's not clear which is which. Someone posted that the tranny outlet line has a splash of pink (hot) and the tranny return line has a splash of blue (cold) to indicate which is which, and I have these marks where the hard lines transition to the rubber hoses part way up the side of the radiator, but where they transition below the alternator both are marked with blue splashes. So much for that theory - guessing that they are a QC signoff. Someone else said to just feel which line heats up first, and I tried that (at the tranny fittings and at several points along the hard lines and hoses) but couldn't feel enough temp difference to be sure. Looking at the passenger side of the tranny, the bottom hard line fitting is below and a bit behind the top one. The FSM A750F section labels one as the "No. 1 outlet oil cooler tube" and the other as the "No. 1 inlet oil cooler tube", but the drawing shows them hovering in space above a view of the driver's side of the tranny when in fact they're on the passenger's side, so the drawing is somewhat ambiguous. Experience tells me to not waste my time asking Toyota. Can someone who knows for sure tell me which is the tranny outlet line (hot) and which is the tranny return line (cold)? The good news is that the Boss approved the purchase of an infrared temp sensor, just so we "could be really sure". I really want it to use on the trailer wheel bearings and brakes at rest stops to spot abnormal increases in temps, so this was a good excuse to help justify the purchase. Also for tracking the temp for ATF level checks. Also for documenting ATF temps before and after adding the cooler.

Any thoughts would be appreciated, so thanks in advance.

I'm thinking about getting the bigger 70274 B&M SuperCooler... I feel if I'm going to put one on the truck, i want it to be REALLY effective.. this one has a 29,200 BTU vs the ones you guys are talking about 70268 @14,400 and the 70264 @13,000. Since winter is approaching, I may just wait till spring.. but re-reading this thread got me looking again. What do you guys think about the higher capacity cooler?

Amazon.com: B&M 70274 SuperCooler Black Aluminum Fluid Cooler: Automotive

Be careful of over-cooling in colder weather. Your transmission needs to operate at a minimum temperature to protect against wear due to lack of lubrication.

I have the medium sized cooler and when air temps are below 55F, the trans temps are too low in my opinion (100F), especially if I am running at low rpm around town (45mph) or cruising freeways. Trans should run above 140F and below 165F for optimum performance.

I have my cooler plumbed in after the radiator to cool during summer months.

That is why the trans fluid is run through a cooler as part of the radiator (in stock form), to warm the fluid in cold weather.

I am thinking about fab'ing a cover for the aux trans cooler for winter weather, that way it reduces the cooling of the auxilary cooler but still has the radiator for cooling/heating.

someone mentioned something about a bypass of some sort due to pressure so the trans fluid doesn't get too cold... so i was thinking if that's true, i could go with a big one.. do you know anything about that?


Here's the quote from B&M "The unit monitors resistance to flow by allowing a controlled amount of ATF to pass through a self-regulating orifice. Controlled by viscosity, thicker ATF is returned directly to lube through two bypass openings in the stacked plate core, while thinner ATF is directed through the core to cool as operating temperatures increase."

Looking at the B&M pdf file at http://bmracing.com/wp-bnmcont/uploa...er_techdoc.pdf, it looks like the "Automatic Transmission SuperCoolers" 70255, 70264, and 70268 (specifically for AT's) have the LPD Low Pressure Drop feature, but the "Universal SuperCoolers" 70273, 70266, and 70274 (for general applications) don't. It specifically mentions LPD in the "Automatic Transmission SuperCoolers" section, but not in the "Universal SuperCoolers" section. I ordered the 70264 to get the LPD. Got the cooler, only to discover that the inlet and outlet tubes are 5/16" instead of the 3/8" that Summit Racing's web site said they would be.

I wonder which ones would have the correct size tubes? this is probably next on my list to do.

We'll be seeing temps down into the single digits when snowshoeing in the Washington mountains, so I really want to use a cooler with the thermo bypass and just stick with the B&M 70264 I already got. I poked around and found some Hayden 11/32" tranny cooler hose that would split the 5/16" vs. 3/8" difference. I'm thinking it would be a little snug on the Toyota 3/8" tubing and a little loose on the B&M 5/16" tranny cooler fittings, but not too bad on either one. Will just get some good quality stainless steel fuel injection hose clamps (not the cheap worm gear kind) and leave it at that.

Should be easy to make up a couple of slip-on sheet aluminum covers for the cooler - a Winter cover with maybe just a couple of 1" holes in it and a Spring/Fall cover with 8 or 10 1" holes.

Summit racing sells 4-1/2' of the 11/32" hose for $8.00.

I'm also ready to pull the trigger on installing a trans cooler. One thing I measured twice was line size. OEM is 10mm = ~ 3/8". No way I would reduce anything. However to each his own.

Here's my shopping cart:

Remote filter
Mr. Gasket cooler
Temp gauge & besel
WS fluid @4qt's

I have the B&M cooler that was supposed to have the cold bypass, but it does not keep the fluid temp up high enough IMO. I used 5/16" hose, it fits over the hard lines OK due to the raised part of the line.

You will want to get hose protection sleeve where the house goes through the sheet metal opening between the radiator and engine bay. I had a hard time finding it in auto stores so I ordered from McMaster-Carr. I bought the braided cover that is used for vehicle electric wiring and good to a high temp, it was $$.

I am using the scan gauge module to monitor trans temps, which uses the vehicle temp sensors, not ideal but saves me a lot of money to drop the pan and install a sensor.

After fitting the cooler in front of the radiator, I then filled the cooler with WS trans fluid to account for the new volume in the system, the cooler took very little fluid, less than 1/2 qt if I remember right.