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Auto trans radiator cooler bypass

66K views 77 replies 31 participants last post by  guzzio 
#1 ·
Just a word here to you folks doing the transmission radiator cooler bypass. DON'T! Water cools about 32x's better and faster than air. The transmission fluid coming from the torque converter to the radiator is at a much higher temperature than the coolant in the radiator. Once the transmission fluid gets to the radiator, it is quickly cooled down to the cooling system temperature. Then it goes to the auxilliary cooler where it gets cooled below cooling system temperature. If you tow, haul or off road, put a second auxiliiary cooler in series with what you have now, or just get a bigger auxilliary trans cooler. It can't be too big, or your return flow rate will drop. If your concerned about cross contamination, get a good aftermarket radiator and rest easy. HEAT is an automatic transmissions worst enemy.
 
#4 · (Edited)
In no way am I trying to be an a** this is just my experience… I did the bypass a week ago. I have an aftermarket trans temp gauge that’s hooked up to the test port. Prior to the mod I was running between 150 and 180 on normal driving. With a trailer I jumped as high as 240. After the mod I’m running between 140 and 160, with the trailer the highest I’ve seen is 210.

I know there’s a ton of variables involved... however the outside temp, roads traveled and load on my truck have been pretty consistent. I have noticed that the transmission fluid cools much quicker when it gets up high then it did before the mod.

Like I said it’s not 100 % a controlled experiment but it’s good enough in my opinion to keep it moded. I forgot to mention I have just the stock cooler, and 100% new fluid 2k ago.

On a side note... I know that fluids cool much quicker in liquid. However, the fluid goes through the radiator at a pretty quick rate. When I replaced my fluid I disconnected trans cooler return line and ran it in to a 5 gallon bucket. I started the truck and dumped the new fluid in to the pan while the old stuff pumped in to the bucket. This was the closest thing I could come up with to get 100 % of the fluid replaced without flushing it at the dealer. I marked each quart line on the bucket so I knew what rate to dump the new fluid at. Muchto my amazement I pumped out 15 qt's in about 60 seconds with the truck in park. I was dumping it in as fast as I could and I barely kept up with it... My point being, I don’t think the fluid sticks around inside the raditaor long enough to make a huge difference. There is only about 1/2 cup total that’s in there at any given time.

Also I talked to a master tech at nissan about putting a bigger cooler in there because of the towing I do. I was concerned about the pressure also. He told me I could go as big as I wanted on a secondary cooler. It really doesnt matter because after it leaves the cooler it dumps back in to the pan. The cooler is the end of the line so just make sure there is enough fluid to fill everything

Just my 2 cents...
 
#42 ·
i think this makes the 3rd person on this forum and a coupl of the other ones who has put a temp gauge on for the atf after the mod. and all have not shown any significant change in temps. definatly no extreme temps after the mod. seems like pretty good proof to me that the mod will be ok for normal driving. i guess time will tell.
 
#5 ·
#12 · (Edited)
so let me get this straight nissanmadness thinks hes right and were all wrong and dont know anything....

i sure as sh!t dont want my tranny takin a dump cuz of coolant getting into the atf. i dont see any disadvantages in running an aux cooler. let alone a bigger one to cool more effective.

nissan must really had not thought that rad/tranny cooler combo very well.
 
#14 ·
I never said that "I", was right, and everybody else was wrong. You're saying that. I stated that I didn't think it was the most efficient way to cool the trans by removing the rad trans cooler from the picture, and installing a second aux trans cooler, "PERIOD". This was for the purpose of preventing cross contamination. Don't read into things that ain't there.
 
#13 · (Edited)
Every car manufacturer has at one point or another run a transmission "cooler" inside of the radiator. Not every manufacturer has had the issue of cross contamination between the radiator and the transmission.

I can from personal experience tell you that when my cross contamination occurred, there was little to nothing I could have done to prevent it. The reason being the transmission cooler inside of the radiator is a closed tube with a hose nipple close to each end at 90*. So, drill a hole in a closed cylinder and then add a hose nipple at 90* and figure out a way to seal it. I don't know if it was epoxy or welded, and don't care. It failed at that joint. The dealer said all others they had seen had failed similarly.

After the dealer replaced my radiator, I did not do the bypass again. I am thinking about doing it, I just haven't decided yet.
I personally think it is done that way as more of a transmission warmer than a cooler. Think about the fact that your radiator temps are in the 180* (if not higher) range, how cool is that? Then factor in that if it was doing a whole lot, why would there be a secondary one?
Researched further and perhaps it does indeed cool to some degree. Put possibly confusing info into "small ninja" text.
 
#22 ·
cooler

I still believe that Nissan knew they had a problem with the matic-f, i think that is why they went to matic-s .

I bought a new radiator for about 160 and changed all the fluid to matic-s from the F. Nissan changer the fluid to full synth for some reason. All their transmissions on all the models 2005-2007 are having problems.

Google up- consumer affairs-- Nissan transmissions
 
#27 ·
After reading all this "opinion", let's filter out the "facts". You make any conclusion you can live with.
A fluid/fluid cooler will have a specific rating for BTU transfer. It will be much higher per inch than for other type coolers.

A fluid/air cooler will also have a specific rating for BTU transfer. It can be defined as BTUs / inch, but will include temperature of the entering fluid and entering air temp.
Nissan chose to use both. On a per inch basis, the radiator cooler is much more effective at removing heat, unless the fluid (antifreeze mix) temperature gets too high.
Every automatic transmission will have a fluid/fluid heat exchanger (that I'm aware of since they started in the 40's) but can operate with a fluid/air exchanger, properly sized for the BTU rejection rate.

A heat exchanger, contrary to "common sense" will transfer more heat with higher fluid velocities ( faster air flow, faster fluid flow). It's just physics.

Nissan obtained poorly manufactured parts from some heat exchanger vendor that no other vendor to my knowledge has had. This is not a normal failure at all.

Elimination of the fluid/fluid heat exchanger and replacement with a fluid/air exchanger "MAY" work if properly sized, but Nissan did size the original system, just bummed the part manufacturing, and I don't have the calculations. I'd prefer to stick with Nissan's original heat exchanger sizing to prevent excursions into temps that may cause damage. If I think the part is failing, I'd change it just as if it were a bad tire.

POP, PE
 
#29 ·
right, but when the radiator goes bad, then you buys a new one. you will just have to replace that one again again again again. makes no sense to me.
 
#32 ·
you could also buy a coolant to atf external aftermarket cooler and bypass the radiator on, but they are expensive. I like the idea of swapping the raditor for a new one, but the ones i've found are also plastic and may be no better than the stock one. At <$200 a new radiator every two years may be a good option. As soon as I can get a TurboDiesel 6M Frontier, I'll be trading in anyway.
 
#33 ·
From what I'm understanding, the failure is with the trans cooler tube, in the radiator. I've also heard the type of trans fluid being used may cause a negative reaction with trans cooler tube. It is plausible, chemicals and additives in a particular type of trans fluid could cause cooler tube deterioration. Most radiators today are plastic, I don't know if an all metal radiator exists for our application. Bypassing the rad cooler should be a temporary cure at best, and here's why. I read where someone did the bypass, and noticed a 10 degree rise in temp, simply because he was behind someone on the highway. Think about being in bumper to bumper traffic, all day city driving, higher or lower elevations. And lastly, cold weather. Will your trans temp be where it needs to be in extreme cold. (think of this past winter) You can do as much damage to a cold transmission as you can a hot one. There are alot of variables involved. I know the one thing we should all do, and I mean as a group. Is that we should start a letter writing campaign to voice our displeasure with Nissan's indifference to this situation. This catastrophic failure of a possible 5.00 part will cost us thousands to repair, should it strike. I've heard of repair bill's averaging around the 6,500.00. This is almost 1/4 to 1/3rd of vehicle value, depending on the model bought. This is crazy. The least they SHOULD do is refund present and past victims of their out of pocket expense, and guarantee owners repair of this type failure in the future. I ask our moderator's to possibly come up with a statement expressing this concern from club members, to where we could all copy, print, sign and date, and mail to corporate Nissan. We should not allow Nissan to Toyota us. Denial, is not just a river in Egypt. There is strength in numbers. What say ye, mod's?
 
#34 ·
I fully agree! I suffered the contamination of the radiator and transmission cooler this year. My truck is now sitting until I can figure out the best way to fix the problem. I have a new tranny and radiator in the garage waiting for the fix. Corporate Nissan told me basically, sorry for your troubles but we here at Nissan decided not to help you.I'm game for this letter.
 
#35 ·
I can only sympathize with your situation. It really stings, when you buy and finance a new truck, to have this kind of thing happen. It shouldn't have happened. Not to a vehicle only a few years old. It didn't happen from neglect or abuse. It happened due to a faulty manufacturing process, cheap materials or both. I still believe Nissan should stand behind this disastrous failure of a rad trans cooler. This bypass being done, should only be short term and temporary. I stand firm in my belief that replacement of the radiator or the cooler at a radiator shop, are the the only two long term solutions. Oh well Sarge, I tried.
 
#37 ·
Those with the tow package have an aux cooler, so the implications of doing the mod aren't the same as those doing the mod sans tow package. There are many threads floating around now that could almost get moved to their own category covering this issues since so many have had this problem. I drove my old 91 Mustang GT slosh box for 10 years or so on the original radiator with ATX cooler built in it without NO problems. I fail to understand why Nissan offering can't do the same. At some point I think a class action law suit may be in order to get the protection from the law from a poorly built/designed radiator and extended warranties to cover the piss poor design.

I guess it will require the anger of those that have been dealt this poor hand of cards to act.

Can we get a forum admin to put all this ATX mess in a dedicated forum or area please so we don't constantly see multiple threads? :)
 
#39 ·
I have no facts about the Nissan-matic fluids. But, I consistently get updates from Voith, Allison, Cat, GM etc... on trans fluids. On many older series of transmissions, the fluids that they normally used are being phased out. The newer fluids have more additives, etc... and do not harm older automatic transmissions. But the newer transmissions MUST have a specific type fluid, my updates also includes a list of the refiners offering the product. Additive packages are the key. So I'm just guessing that Nissan may have upgraded the type of trans fluids for the automatic transmissions from F,J, to S. I haven't heard of any transmission failures due to fluids, just from the trans rad cooler.
 
#40 ·
tranny

I don't mean to keep kicking this , but my thought is that the internal cooler in the radiator is a part that is more than likely in many radiators, i doubt if Nissan has their own internal cooler.

I have not read or heard about other mfr having this problem , all nissan models 05-07 are having this problem. I don't know if the --xt--alt--and other models have the same tranny cooler in the radiator , i doubt it.

The only thing common is the matic-f fluid.
 
#41 ·
I don't mean to keep kicking this , but my thought is that the internal cooler in the radiator is a part that is more than likely in many radiators, i doubt if Nissan has their own internal cooler.

I have not read or heard about other mfr having this problem , all nissan models 05-07 are having this problem. I don't know if the --xt--alt--and other models have the same tranny cooler in the radiator , i doubt it.

The only thing common is the matic-f fluid.
I hear Xterra's, Pathfinders, etc... are having this problem too. It's not just the Frontiers. The radiator dimension's may not be the same for all models, but the manufacturer or vendor might be, the one and only. Might be some some real poor QC on that assembly line in, "CHINA"! As you specify F fluid, the years of failure cover 05-07, mine has J fluid. No telling, as your claim is plausible, the ONLY way we'll ever know is if, Nissan comes clean about this whole mess. I read the all the pages from the Consumer Affairs complaints site you mentioned, WOW!... what horror stories. Fact, not fiction. But anyway, don't feel bad about kicking this thing around, sometimes it's what it takes to bring something to light.
 
#45 ·
I was running Amsoil when mine went out. Dealership was not told this due to them jumping on that info as a way out of fixing it. I've been told that Amsoil tranny fluid is one of the better ones.
 
#47 ·
ins

I look at it as a insurance policy, like auto insurance or medical ins ,now things are great until you need it, if you don't have it it would be too late.

No one knows how long it would take to ruin the tranny if anti/water gets into it, is it a hundard miles or a thousand miles.

As everyone knows 300 is a lot cheaper than 5000, also piece of mind not having to worry about it , one less thing to worry about.
 
#48 ·
I did the modification about 2 months ago. First off, I did the modification because I was getting the vibration when shifting into OD. When I did that, I realized my transmission fluid was a dark brown. I took it to a transmission shop who put it on the computer, and found nothing wrong with the transmission. They changed the transmission fluid, (didn't do a flush, they said it had too many miles), and vibration went away.

Fast forward 2 months... today a fluid line (I think) blew out. It looks to be the near the right side of the oil cooler behind the grill. I'm wondering if, when the fluid was changed, they put the specified amount of fluid in, but since I've decreased the capacity by bypassing the radiator, it was building up more pressure than normal. I don't know.

Hopefully tomorrow, we'll get the line changed, and that will be the only the problem. Is that a formed hose, or can I get hose from an auto parts store? But once I get this worked out, I'll probably forgo the bypass and replace the radiator in the near future. I have a 2005 Frontier 4x4.
 
#49 ·
hose

I don't think it is a formed hose, i have put external coolers on many of my cars/trucks here in AZ, the cooler mfr in their instructions say do not kink or put too sharp of a bend in the hose, if the hose you use is a little longer than you need it will form with no problems. Just a piece of the bad hose off and take it to autozone with you and you will get the correct size.

I have wondered about Nissan transmission pressure (?), i have never seen a dip stick that has to be bolted down. W/O the bolt , will it blow out ?
 
#50 ·
I know this thread is old, but does anyone have any suggestions for a radiator replacement? I checked the part number in my 08 and it is the same as the 05 radiators. I know nissan has an updated radiator, but theirs is in the neighborhood of $400.00. I have found Koyo and CSF radiators out there....Any experience with these?

Thanks,

Adam
 
#51 ·
i bought after market rad for my 2007 4 cyl ( 25000 mi ) because of the rad coolent getting into peoples auto tranny's , then i changed my tranny fluid to the new nissan fluid . also installed a tranny fluid cooler between the rad out and tranny.

i think nissan knew they had a problen with the older trans fluid , thats why they changed to a better fluid that didn't eat thru the fluid cooler in rad.

i think i bought the rad from rockauto for about $140 , worked great.:itsfriday:
 
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