AUX trans cooler / Bypass or don't bypass... - JeepForum.com

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post #1 of 32 Old 07-07-2013, 01:02 AM Thread Starter
dave564
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AUX trans cooler / Bypass or don't bypass...

Well that is the question.

I just ordered from Summit a new B&M 70264 for my stock 2000 XJ. The trailer that I will be pulling is a 10x6 enclosed weighing in at 2200#.

Should I put it on the return line of the OEM, or just go ahead and bypass it all together??

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post #2 of 32 Old 07-07-2013, 06:25 AM
Newtons3
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This is always a spirited debate. In my experience it is best to remove the transmission fluid from the radiator. Generally, the cooler the fluid the better. I have seen reports that say the fluid should have a target temperature of as low as 140 degrees (outlet side of the cooler) to prevent degradation of the seals and clutches. Regardless, it makes no sense to me to soak the transmission fluid in engine coolant running 165-230 degrees in an attemp to cool it down. It would have to be dangerously hot to have enough temperature differential to effectively cool it off at all. In addition, that heat only adds stress to an already heavily taxed cooling system. The lowest temperature achievable (at the outlet of the radiator cooler) will be the operating temperature of the engine coolant. That just is unacceptable to me. there are some who say the factory set-up aids in the warm-up of the transmission. I live in south Louisiana though where shorts, air conditioner, and going barefoot are not uncommon at Christmas. Warm-up is a non-issue for us.
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post #3 of 32 Old 07-07-2013, 03:33 PM
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In hot climate, I really see no reason for the tranny oil to be routed first through the radiator.

However, I've had some problems to get the tranny up to operating temps fast enough in cold weather with the radiator bypassed, so if you live in a climate with true winters, I would not bypass the radiator; first through the rad. then through the aux tranny cooler, and back to tranny. It helps heating up the tranny fluid, and it also helps keep it hot enough. Driving on the highways (or even city driving) on -20*F, running only an aux. tranny cooler may result in the tranny not reaching proper operating temperature.

Coolant temperature inside the radiator is actually suprsingly low. However, under high loads when both the tranny fluid heats up and the engine creates a lot of heat, radiator coolant temperature is too gigh, and its cooling capacity too low to prevent the tranny fluid from getting too hot -> aux. tranny cooler is always a good idea for most automatic transmissions.

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post #4 of 32 Old 07-07-2013, 04:25 PM
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IIRC, the instructions that come with the B&M #70264 cooler say "for max cooling efficiency, install the auxiliary cooler inline with AND after the factory cooler" or something to that effect. That's what the instructions said that came with our B&M 70264. Personally, I would never bypass the OE factory cooler unless I installed a tranny fluid temp gauge to keep tabs on things. I guess one could always say "but what does B&M know".

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post #5 of 32 Old 07-07-2013, 04:42 PM
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What temp would you be looking for? What do you consider an acceptable range?
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post #6 of 32 Old 07-07-2013, 05:02 PM
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Around 150-175 F can be considered safe and acceptable, long term running a lot colder or hotter isn't good - especially hotter. I've seen figures as low as 100 and above to be a good operating temp for automatic transmissions.

I know for a fact the stock cooling setup for ie. ZJ niners isn't close to being enough to keep the tranny fluid cool during summer and/ or heavy use. Tranny temp rises to well over 210F in doing just city driving in 85F weather, and that with a cooling system in top notch condition.

I got lower tranny fluid temps on both of my XJs with the radiator bypassed, aux cooler in front of radiator where the viscous fan is.

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post #7 of 32 Old 07-07-2013, 05:21 PM
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Quote:
Originally Posted by Newtons3 View Post
What temp would you be looking for? What do you consider an acceptable range?
I'm not looking for a specific temp......and I'll go along with whatever the engineers consider an acceptable range and they seem to think that the rad tranny cooler works well enough under most driving conditions but for max tow rating, they decided a auxiliary (not a replacement) cooler should be installled in-line with and after the primary rad cooler. So with that said, if one mounts a auxiliary cooler in-line with and after the factor rad cooler (the same way Jeep installs their optional auxiliary tranny cooler and the way B&M recommends to install their auxilary cooler), the tranny probably ain't going to run any hotter than is acceptable to the engineers. Again, no way I'm going to bypass the factory OE set-up without a tranny temp gauge. In fact, I'd install the tranny fluid temp gauge 1st......get some base-line temp readings under various driving conditions (including towing) with the stock set-up, then, and only then, install a replacement cooler and keep close tabs on the tranny fluid temp gauge. I'm also guessing during the tranny design phase that a fluid temp gauge was used to monitor temps but I don't know that for a fact, just seems logical.

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post #8 of 32 Old 07-07-2013, 05:27 PM
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My tranny cooler is installed with no radiator loop. I have a temp gauge too. Regular winter driving the temp is 125 - 175, regular summer running temp is 140 - 180. I'd hate to ADD heat to that by running it through the radiator. I know that's how it was built, but anything hotter is too hot for me. It has been as hot as 280, slow and go, running with a load or towing.

If I lived in Michigan (or ND, SD, MN etc.) I'd keep the radiator "heat exchanger" in the loop but it rarely to never freezes here and if it does, it's a soft freeze. I've lived here 30+ yrs. and the coldest it's ever been is about 20F for a night or two. The usual "snow line" is about 1000-1500 ft. above us. Occasionally it snows here, once or twice a year.

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post #9 of 32 Old 07-07-2013, 06:16 PM Thread Starter
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Ok, I have no facts to back this up, but this is how I understand things work.

In a perfect world, the radiator would cool the coolant from engine operating temp all the way down to ambient temp of the air passing through it. Now in the summer I bet that the radiator has a high enough BTU rating to dissipate the 210F down to within say 20 degrees of the outside temp. (For argument sake lets say it is 80 degrees today.) In the winter I would have to guess it might be able to get it down to within 50 Degrees, maybe lower depending on how much coolant is being allowed to go past the thermostat.

Since the trans cooler is in the cold tank on the radiator, it can only cool the fluid to within a couple of degrees of the coolant surrounding it, which in theory should be pretty close to the ambient temperature of the current weather. The problem happens when the transmission starts to work hard (IE: pulling a trailer) the transmission cooler does not have a sufficient BTU rating to handle the extra heat. (Not to mention that ALL the transmission heat is then being sent back into the cold side of the engine’s cooling system.)

I don’t know how much credence can be given to the stock cooler preheating the fluid, unless we are talking outside temperatures way below zero like Timo 90XJ stated. Here in Michigan the coldest I see is about -5 in the morning, then it climbs into the teens. So even if you bypass the OEM cooler, it is only going to be able to cool to about 20 to 30 degrees of outside temp anyway, which for me would put the return fluid in the range of 40 to 50 degrees at its lowest.

With all that being said, you can only “cool” the fluid, you cannot SUPER COOL it my adding cooling capacity. Unless it is extremely cold (-15 and below) I would think for practical purposes preheating the fluid in the “COLD SIDE” of the radiator to get to an operating temperature is not a concern for the most of us since it is obvious to me now that the transmission has a VERY WIDE operating temperature range, unlike the engine.

So now I wonder what the BTU rating of the stock cooler is v/s the 14,400 BTU rating of the B&M. If the B&M cooler is double or triple the rating of the stock unit, do you really need it in the system? Especially when pulling a load.

OK YOU BACKYARD SCIENTISTS, LETS HEAR YOUR REBUTTALS...
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post #10 of 32 Old 07-07-2013, 06:34 PM
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Quote:
Originally Posted by Timo_90xj View Post
Around 150-175 F can be considered safe and acceptable, long term running a lot colder or hotter isn't good - especially hotter. I've seen figures as low as 100 and above to be a good operating temp for automatic transmissions.
This is spot-on with all the information I have, which is pretty extensive.


Quote:
Originally Posted by djb383 View Post
I'm not looking for a specific temp......and I'll go along with whatever the engineers consider an acceptable range and they seem to think that the rad tranny cooler works well enough under most driving conditions but for max tow rating, they decided a auxiliary (not a replacement) cooler should be installled in-line with and after the primary rad cooler. So with that said, if one mounts a auxiliary cooler in-line with and after the factor rad cooler (the same way Jeep installs their optional auxiliary tranny cooler and the way B&M recommends to install their auxilary cooler), the tranny probably ain't going to run any hotter than is acceptable to the engineers. Again, no way I'm going to bypass the factory OE set-up without a tranny temp gauge. In fact, I'd install the tranny fluid temp gauge 1st......get some base-line temp readings under various driving conditions (including towing) with the stock set-up, then, and only then, install a replacement cooler and keep close tabs on the tranny fluid temp gauge. I'm also guessing during the tranny design phase that a fluid temp gauge was used to monitor temps but I don't know that for a fact, just seems logical.
I have two gauges. One on the outlet and one on the inlet. I have this baselined. I don't go with non application-specific recommendations from anybody and just assume they are correct. First I need a target temp. range and I address the problem that way.

Quote:
Originally Posted by Paradise XJ View Post
My tranny cooler is installed with no radiator loop. I have a temp gauge too. Regular winter driving the temp is 125 - 175, regular summer running temp is 140 - 180. I'd hate to ADD heat to that by running it through the radiator. I know that's how it was built, but anything hotter is too hot for me. It has been as hot as 280, slow and go, running with a load or towing.

If I lived in Michigan (or ND, SD, MN etc.) I'd keep the radiator "heat exchanger" in the loop but it rarely to never freezes here and if it does, it's a soft freeze. I've lived here 30+ yrs. and the coldest it's ever been is about 20F for a night or two. The usual "snow line" is about 1000-1500 ft. above us. Occasionally it snows here, once or twice a year.
X2. This is exactly how I feel and what my experience backs up. I could see needing to add heat if I was somewhere with VERY harsh winters, but, alas, we don't even have a recipe for ice here.
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post #11 of 32 Old 07-07-2013, 06:49 PM
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Quote:
Originally Posted by dave564 View Post
Ok, I have no facts to back this up, but this is how I understand things work.

In a perfect world, the radiator would cool the coolant from engine operating temp all the way down to ambient temp of the air passing through it. Now in the summer I bet that the radiator has a high enough BTU rating to dissipate the 210F down to within say 20 degrees of the outside temp. (For argument sake lets say it is 80 degrees today.) In the winter I would have to guess it might be able to get it down to within 50 Degrees, maybe lower depending on how much coolant is being allowed to go past the thermostat.

Since the trans cooler is in the cold tank on the radiator, it can only cool the fluid to within a couple of degrees of the coolant surrounding it, which in theory should be pretty close to the ambient temperature of the current weather. The problem happens when the transmission starts to work hard (IE: pulling a trailer) the transmission cooler does not have a sufficient BTU rating to handle the extra heat. (Not to mention that ALL the transmission heat is then being sent back into the cold side of the engine’s cooling system.)

I don’t know how much credence can be given to the stock cooler preheating the fluid, unless we are talking outside temperatures way below zero like Timo 90XJ stated. Here in Michigan the coldest I see is about -5 in the morning, then it climbs into the teens. So even if you bypass the OEM cooler, it is only going to be able to cool to about 20 to 30 degrees of outside temp anyway, which for me would put the return fluid in the range of 40 to 50 degrees at its lowest.

With all that being said, you can only “cool” the fluid, you cannot SUPER COOL it my adding cooling capacity. Unless it is extremely cold (-15 and below) I would think for practical purposes preheating the fluid in the “COLD SIDE” of the radiator to get to an operating temperature is not a concern for the most of us since it is obvious to me now that the transmission has a VERY WIDE operating temperature range, unlike the engine.

So now I wonder what the BTU rating of the stock cooler is v/s the 14,400 BTU rating of the B&M. If the B&M cooler is double or triple the rating of the stock unit, do you really need it in the system? Especially when pulling a load.

OK YOU BACKYARD SCIENTISTS, LETS HEAR YOUR REBUTTALS...
Rebuttal: There is no way the "cold tank" on an operational radiator is at ambient temperature. Engineers shoot for around a 40 degree drop from inlet temperature in design, give or take. That being said, my fluid is entering my radiator at 215 (average, actual 205-220). If we assume we have an overachieving cooling system and we get a 50 degree temp drop, that means the fluid in the "cold tank" will be around 165. That's on the upper end of the spectrum of operating temp for transmission fluid for me. Most of the time, you'll be heating the transmission fluid and possibly causing problems. When you do need to dump heat, the exchange will only bring you down to my upper limit. My gauges showed this on two of my AW4's. The one I have now was running around 215 in the summer. Also, transmissions running at speed generate little heat. The majority of the heat comes from the converter when it is unlocked and from the pump. So unless your clutches are slipping, in which case your transmission is or shortly will be toast, most of the heat is generated while accelerating.

Not one to be without a solution, my cooler is a Hydac hydraulic cooler, isolated from the radiator and the grill with an 8" Spal thermostatically controlled fan on it. Fan comes on at 160 degrees. Works extremely well and I've been unable to overheat the transmission since installation. Will have write-up, pics, etc. when the Cherokee hits the road again.
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post #12 of 32 Old 07-07-2013, 07:01 PM Thread Starter
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Also consider this!!

I was originally going to use a B&M #70264 I pulled from an old U-Haul truck I found in a junk yard, but it only had inlets for 1/4" pipe that Ford uses for trans lines. (SEE: http://www.jeepforum.com/forum/f11/x...ideas-1517948/

Ford was not concerned about preheating the fluid in the radiator in the winter, they only used the B&M cooler, there was no pass through on the radiator. I am starting to think that these bolt on cooler manufacturers "TELL" you to put it in line with your stock cooler more to cover THEIR *** legally than out of mechanical necessity..
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post #13 of 32 Old 07-07-2013, 07:22 PM Thread Starter
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Quote:
Originally Posted by Newtons3 View Post
Also, transmissions running at speed generate little heat. The majority of the heat comes from the converter when it is unlocked and from the pump. So unless your clutches are slipping, in which case your transmission is or shortly will be toast, most of the heat is generated while accelerating.
You make a real good point there. For all practical purposes I don't think those of us that aren't in extreme sub zero winters need to worry about making the fluid too cold. After all, cold fluid is thicker, which means you will have higher hydraulic pressure on your clutches, and higher oil pressure on the bearings. With every transmission I have had that is a good thing.

My Cherokee is no rock crawler or mudder, it is the toy's tow truck. For my needs I think I am just going to run the B&M by itself. I can always hook up the stock cooler later if I have problems.
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post #14 of 32 Old 07-07-2013, 09:06 PM
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The coolant in the "COLD" side of the radiator is hot...about 192 . The coolant never gets even near ambient temperature, once the t-stat opens it's open, it doesn't cycle on/off, so ALL the coolant circulating at ~192-and up. It cools some as it passes through the radiator but not down to ambient temperature. It's just a 1 1/4" tube that the tranny fluid travels through, surrounded by HOT coolant, nothing more complicated, no fins, ribs, no network of capillary tubes. So the transmission fluid in the radiator tube is heated.

The tranny fluid WILL get too cold if you're driving in sub-Z temps and don't have the radiator in the loop. Thicker cooler fluid is not necessarily better.
If you live in Florida, or somewhere that's always warm, the tranny doesn't need any help generating heat. E.G

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post #15 of 32 Old 07-07-2013, 09:28 PM
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I thought t-stats "hovered" in an infinite number of more/less open positions between closed/full open, no?

Man Law - hoods should be raised at least once a week.....have a look see.
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