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Old 01-17-2012, 12:21 AM   #1
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transmission cooling at low speeds

Preface: This is an '08 ford factory rebuilt '99 v10 and 4r100 with currently the (likely original) stock transmission cooler. Both grille and bumpers are stock. I'm reading the transmission fluid temperature as via a scan gauge, which should be, if I'm not mistaken at the output side, so the highest reading possible.

My issues are with low speed climbing, both on steep winding paved roads, and crawling in 4 low.

When climbing slowly (35mph and under) I invariably see the transmission fluid temperature climb, apparently without bound. Once, not wanting to stop on a steep sandy section (tough for the engine/transmission, very likely to get stuck if I stopped) I pushed through and watched the temperature spike from 200-240 degrees in less than a minute. If I can keep the speed closer to 40mph things stay under 200 degrees. Currently I'm pulling over to let things cool as the fluid approaches 220. Cooling down takes 20-40 minutes at a time, and has tried my patience to the point that I'm going to do something about it.

At speed, even towing (a ~5k lbs flatbed over Donner Pass topped out at 220; not great, but livable) the cooling more or less works.

The fact that things stay under control at speed suggest that more air-flow at low speeds would help. The main engine fan does not seem to engage when only the TFT is high. Just looking at the cooler location with respect to the main fan, it doesn't look like the transmission cooler is in the direct path of the air flow that the main fan would generate anyway.

I suspect that I want a fan on the transmission cooler, likely along with a larger cooler. I'd also be willing to go with a larger pan, but it doesn't sound like that's done much for anyone. I'll likely wrap the exhaust close to the lines, but while non-optimal, it doesn't strike me as the sole source of the problem.

The Tru-Cool MAX 40k GVW seems like a fairly straight forward replacement, and I can even find a thermal fan switch for it. However I can't seem to find much information on which fans might work, or whether folks are just wiring it up so that it will trigger the clutch on the main fan. Any pointers to fans that might work, or how to trigger the main fan clutch would be greatly appreciated.

Questions I'm having a hard time answering:

That Tru-Cool MAX cooler is still much smaller than what the pickups come with. There's plenty of room downwards. Do I really not want to look for something closer in dimensions to the stock cooler in an f350?

Is there a simple way to figure out if the bypass valve on the transmission is doing the right thing and not sabotaging things at the wrong moment? Or is that generally not an issue? I suppose I should try poking around with a thermometer the next time I'm waiting for things to cool down.
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Old 01-18-2012, 12:59 AM   #2
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Re: transmission cooling at low speeds

Here's a shot the the bypass I'm not quite willing to trust without verification:



The pan seal's been seeping a bit (though no measurable loss of fluid in 4k miles, I'll sort it, but mostly because I'm a bit OCD about leaks). What's not clear is if the mess on the bypass is from the line going to the cooler, or just stuff that seeped out of the pan seal.
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Old 01-18-2012, 09:53 AM   #3
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Re: transmission cooling at low speeds

I put the TruCool 40k in. Almost a direct replacement. My temps were similar before. Skip the TruCool thermostatic bypass. It's a POS. Mine caused problems, and I read that is common among buyers. I just run a grill insert in winter.

I've still considered a small electric fan for low speed and idling, but mostly for better AC performance.
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Old 01-18-2012, 11:48 AM   #4
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Re: transmission cooling at low speeds

Your temps aren't out of line. I wouldn't worry about a short term trans temp of even 250.

When in lo range, off-road, keep the trans in a lower gear to keep the revs up. If the engine is at 2000 rpm or so, the torque convertor is essentially locked up and your trans temps will be lower. At light loads most of the trans heat is from TC slippage.

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Old 01-18-2012, 10:12 PM   #5
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Re: transmission cooling at low speeds

Well, I'm keeping the temperature in line by shutting it down and letting it cool down for 40 minutes or so. right before I stop I'm usually watching the temperature climb 10-20 degrees in less than a minute. I'd prefer to see things stay under 200 if possible without stopping, but I'd settle for under 220 as well. It's the fast, apparently unchecked, rise in temperature that's convincing me to keep an eye on things.

I should also point out that the climbs leading to this are long, steep and winding and would be life accomplishments for many cyclists. Probably not what Ford had in mind when they designed this thing, but unfortunately exactly where I want to go camp.

In terms of driving habits, I've been watching the slip rate (again scan-gauge) and am resorting to low gears as much as I can in these situations, usually first or second. Neither ever truly lock up; though I believe that's normal/correct for the 4r100 unless I hack it somehow, but with care I do manage to keep them around 1:.9 or so.

About the only thing that's helped is running in 4 low in second or third. Still not enough, but I'd be willing to suggest that it's actually better.

That and a couple other things are also making me wonder if enough fluid is getting pumped around at low speeds. If that's my problem, then a fan won't help all that much. In fact other than figuring out how to move more fluid, which, and I don't know that much about automatic transmission, would be far more involved that just adding a pump, there's not much to do other than delay the rise in temperature. Though I suppose the climbs do end, and if I can push out the critical time by 4-8x I'd probably be fine.

I'm still interested in hearing from anyone that actually has a fan.

Also, the idea that I'm really only delaying the spike puts the larger pan back on the table. So now I'm thinking cooler, pan and fan.
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Old 05-13-2012, 11:12 PM   #6
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Re: transmission cooling at low speeds

I installed both the Tru-Cool Max 40k transmission cooler (hereafter "cooler") and the supplied thermal bypass (despite the warnings, thanks Carringb, which were ultimately dead-on, I was strongly urged to do so by my ME consultant).

Here's what I learned that I did not find documented elsewhere:

The bypass (blue anodized thing) never fully closes whether or not I run the hot side further away from (as labelled) or closer to the thermostatic valve. This allows the transmission temperature to shoot up to 200 degrees F much much faster than with the old cooler. Checking the lines, the cooler was taking on warm fluid and putting out downright cold fluid, but mostly hot fluid was going directly back to the transmission. That is obviously totally toxic. -- I sure wish I hadn't made two revisions of a mount for it before determining that. In any case, it's back out of the van now.

The cooler works quite well at low speed, even without a fan. Winding up a 1600' 7% climb at speeds between 20 and 25 mph, I never saw the temperature break 184 degrees F. With the factory cooler this would have been impossible.

Just cruising around on flat ground as well as a short bit on the freeway (65mph) shows 140-145 degrees F.

Fitting a fan, and I'll try life without one for a bit, with this cooler without making brackets that somehow move it as far back as possible, will push the fan out into space taken up by the stock Ford grill. The stock grill could either be cut, or swapped for a lower profile aftermarket grill.

Note: All my temperature readings are taken from a scangauge.

I also got some IR readings of input and output temperatures of the cooler. For the moments when I measured it, it showed a drop between 20 and 40 degrees F, mostly close to 30 degrees F.

Finally, not all my projects take this long, but apparently the van doesn't get much use during winter and spring, so this hasn't been a priority until now.
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Old 05-14-2012, 10:23 AM   #7
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Re: transmission cooling at low speeds

I just had the factory transmission cooler on my '01 Excursion (7.3L w/4R100 trans) replaced with a factory transmission cooler from a 6.0L, which is something like three times the size of the stock 7.3L trans cooler.


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Old 06-02-2016, 01:01 PM   #8
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One more bit of data, collected the really hard way:

My cooling issues have been, in hindsight related to clogging the coolers with fine metal dust. (Which is not really a good thing to have in a transmission). Towards the end of this transmissions life I learned to back-flush the coolers manually and then put a filter I swapped out regularly before the coolers. That helped get rid of the runaway situations.

At low speeds I still need a fan, but cooling things down happens really fast when everything is working. Not 10 minutes of pulling over, more like 2 minutes.
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Old 06-02-2016, 06:27 PM   #9
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Add a 6.0 cooler
Install a manual switch on the fan by tapping into the light blue wire in the fan harness
It will take a few seconds to cut on and about a minute to cut off after switch is turned off
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Old 06-02-2016, 06:32 PM   #10
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That's a manual override on the fan clutch? I've wanted to do that for a while.
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