Transmission cooler: to by-pass the radiator or not to by-pass it

I keep reading posts here where members are encouraging people to just by-pass the radiator transmission fluid cooler to avoid the strawberry milkshake problem. First, just spend the $120 to buy a new radiator. Koyo rads are on ebay all day long. That will give you some peace of mind. now also add the extra B&M aux cooler, but do not just bypass the radiator. The radiator cooler serves two functions. It warms the trans fluid to operating temp quicker than the transmission can do on its own, which help prolong its life. Second, it cools the transmission better than just an air-cooled aux cooler can do. A liquid to liquid cooler is far more efficient than an air to liquid cooler. If you overheat the transmission, it will die quickly. Why then add a cooler to the transmission line?? Because the optimal temperature for a transmission is around 160-180 degrees. The radiator is typically at 180 degrees. So by adding the cooler inline "after" the radiator, you bring the temp up quickly using the engine coolant, but then keep it down below 160 degrees by cooling it again through a 2nd cooler. The B&M cooler can only lower the oil temperature by 20 degrees +/-. I've been able to monitor this effect on other cars I've had with a diagnostic interface and always had to restore the radiator cooler because the transmission temps would soar above 220 degrees with just an aux cooler alone.



I pulled this from an AMSoil site. Look at the conventional oil graph.

OMG i better run out to the parking lot and tell my 194k transmission that hasn't had radiator cooling since 124k that its going to die soon! lol sorry had to over react at least a little. :

While I do agree with what you are saying to some degree, I have experienced no first hand problems with my cooler, and no radiator help to warm the transmission or aid in cooling. This has included several trips towing loads at or over the recommend range of the vehicle, for 12+ hours at a time through the rocky mountains even.

Also, you are not mentioning the size, design or placement of the aftermarket cooler which was tested as the only means of cooling the trans, or if it was even the same transmission that was tested. Test data can lead you to some very inaccurate results if you have too many variables.

First, a transmission cooler is ~$50. Not everyone has the extra $70. Especially when the $50 option will work.

Second, there are literally hundreds of people here running just an auxiliary cooler with no problems at all. And some have a temp gauge. And some have added an additional temp gauge.

Funny, but not exactly scientific now is it. We all have stories to tell. For instance, my idiot sister never changed her motor oil on her 280zx for the first 70,000 miles and I didn't catch it until the low oil light came on. No her motor did not melt down but we can all agree its not the ideal way to treat your vehicle.

The simple truth is this. The transmission was engineered to operate within a certain temp range. It needs to warm quickly to function properly and stay cool to prolong its life. You can run it hot for a while but it will fail prematurely (whatever that is for your truck). To argue this point is...

DrCoffee, I decided not to do the bypass for the same logic.

Where I live probably influenced my decision most.

Living in AZ with +115 degree summers, I wanted maximum cooling effect.

I bought a new Koyo radiator and added the B&M 70264 cooler in line (no bypass). No risk of pink milkshake with a new radiator.

Those that live in cooler climates, might get away with the bypass with little ill effects.

But, wanted to say I enjoyed reading your write up with data to back up your point.

Good job.

I have run it both ways - through the radiator on my taco and bypassed completely on my 4runner. Both used the same cooler (B&M that BFAD recommends). Both are the 3.4 (Taco is supercharged). Obviously the taco transmission runs hotter and warms up quicker but both transmissions work fine and are flushed regularly. I have a small cover that I used to partially cover the transcooler in the winter on the 4runner - helps keep it warmed up to that sweet spot of 165. Without the cover in the spring it runs very cool. I have seen temps peak around 200 on the runner, wheeling hard in the hottest months of the summer (temps around 110) and I have seen the trans peak at 206 (scanguage II).

My theory on this is that since you are paying more attention to your radiator (and trans cooling) with regular changes, etc that most people prolong your life. At the very least, the additional capacity of your transcooler, regardless of where you install it, helps.

My 2 cents.

Drcoffee said:

The simple truth is this. The transmission was engineered to operate within a certain temp range. It needs to warm quickly to function properly and stay cool to prolong its life. You can run it hot for a while but it will fail prematurely (whatever that is for your truck).

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You keep saying this, but can you back it up with facts? Not trying to be a dyck, it's just that you seem very confident.

Also, coolant temp is measured at the top of the block, at it's hottest condition, correct? The coolant in the bottom of the radiator (where the trans cooler is) is much cooler. In fact, it doesn't even begin to warm up until the thermostat opens, which could be a long while after you've started driving during colder months.

So...

Qyota said:

You keep saying this, but can you back it up with facts? Not trying to be a dyck, it's just that you seem very confident.

Also, coolant temp is measured at the top of the block, at it's hottest condition, correct? The coolant in the bottom of the radiator (where the trans cooler is) is much cooler. In fact, it doesn't even begin to warm up until the thermostat opens, which could be a long while after you've started driving during colder months.

So...

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Good points, the tranny fluid won't benefit from the heating effects of the coolant until the engine is warm enough for the t-stat to open, so that removes much of the benefit to the stock tranny cooler IMO.

I bypassed, and I also went with the smallest B&M I could find, as I live where it's COLD 1/2 the year, and so far the only towing I'll be doing is in those cold months.

Drcoffee said:

Second, it cools the transmission better than just an air-cooled aux cooler can do. A liquid to liquid cooler is far more efficient than an air to liquid cooler.

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Can you please explain this a little further? I understand that a liquid to liquid cooler is more efficient than air to liquid. However, our radiator/trans coolers are air to liquid to liquid. If the air cools the coolant and the coolant cools the trans fluid, it becomes more inefficient than an air to liquid cooler. Also the liquid that is being used to "cool" the trans fluid is generally much higher than on the input side of the radiator than the optimal 160* temp that you comment on. Thus, resulting in higher temps than if the fluid had not been "cooled" by the coolant.

I am just confused how this system could be less efficient or would cool less than a stand alone unit.:shrug:

So the coolant enters the top of the radiator heated by the engine. It decends thru the radiator and cools well below the 180 op temp of the motor. The engine modulates it's temp by use of a thermostat which is hardly ever wide open. It slows the coolant down so that only enough coolant re-enters the engine to maintain 180 degrees. If you don't believe me, take out your T-stat and see how much cooler your engine runs. If you accept that reality, then you understand that your coolant in the radiator is less than 180. That is why your trans fluid will come out of the transmission hot and in 12" be cooled by the coolant enough to return to the transmission.

So now that we have covered the basics, let's go one step further. The trans cooler in the radiator is a tube about 1" round by 12" long. Can we agree that it is considerably smaller than the engine radiator? Yes we can. Let's leap forward and just agree that a small trans cooler immersed in liquid is far more efficient than the 3'x3 radiator which cools the motor by forcing air across its surface.

Maybe someone else can explain it better than I, but a google search may be beneficial.
:bluejump:

let me see if I have this correct.

you are using Amersols data as evidence that Toyota designed their cooling system in a way that causes it to run on average at 180 F or slightly higher AND this will result in decreased trans life.

=> Because of the fact that Amorsol says the trans fluid should be 160F, then the factory specs are wrong and Toyota's engineers were wrong.

Sorry but I simply don't buy into this argument as it was presented. I think Toyota's designed is pretty good despite the pink milkshake threat which is rare. IMO, these trans are some of the best in the auto industry and typically go 150-200k with NO problems.

I replaced my radiator at 190k miles with a Koyo and kept it stock. I don't believe I need the bypass. I live in San Diego, CA. My 4Runner has 209,000+ miles and no slippage. I have owned it since 2003.

:bat:

(sent from Droid X2)

I think your argument has derived to being that the radiator cooler is more efficient than the aftermarket cooler.

In your original post you claim that the temperatures will soar above 220 degF if you use just the aftermarket cooler.

Not sure how you can be so sure? I want to believe you, but all evidence points otherwise. Convince me.

I bypassed mine. I agree that you're probably okay with just replacing the radiator and calling it a day. But, new parts do fail sometimes. Just the simple fact that it could happen was enough for me to bypass it so that it can't happen.

OP your logic is not entirely accurate. having been a tech and worked for several shops(from independent tuners to dealer to fleet) i can assure you that the factory cooler only helps regulate the temp. it is not enough to cool the trans when towing or having much of a load on the motor, also what happens when your motor overheats? yeah your tranny then starts to over heat and the two will compound one another exponentially. i have experienced this. i run dual coolers, one with an electric fan on my it and i have an inline gauge. (see http://www.toyota-4runner.org/3rd-gen-t4rs/105400-rescue-runner-build-thread.html to look at the coolers) i see temps of around 145-160 while cursing down the freeway at 60+mph even on cool days. some days if its like only 30* out or so i can watch it drop to around 110* if im not moving a lot.
but the flip side is if im out wheeling where i dont have a lot of air movement and i have a high/heavy load on the trans -4lo armored and E rated 285s, i can still watch that temp gauge climb well over the 220* mark. i have also overheated my truck in stop and go traffic last summer, while my trans stayed under 200* if i had not bypassed my radiator my dual coolers would have done nothing to help me as you have stated liquid to liquid is a much greater power than air to liquid.
the stock cooler was designed to cool the truck with out a load, meaning not having 5 people in it going up a hill, not having armor on your truck, not having over-sized tires, not towing(even under the towing capacity) and most defiantly not a combination of all of these. the stock cooler is basically useless unless you are a stock rig and never tow. and if you tow and are modified ie lifted, bigger tires, and armored ect i would get rid of the "cooler" in the radiator as you are now creating a weak link in your trans cooling system.

the plate in the radiator that separates the trans fluid from the antifreeze is weakened everytime temps rise and fluctuate. thats one of the ways these falures are happening over time it weakens the material and you combined that with old age and people not "flushing" their systems, you have a disaster waiting to happen. now the heat differences and extreme temps again are not so much of an issue in a stock rig so i can see the value of keeping they radiator in the "system"

the kid said:

OP your logic is not entirely accurate. having been a tech and worked for several shops(from independent tuners to dealer to fleet) i can assure you that the factory cooler only helps regulate the temp.

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No disagreement here.^ My only point is don't delete the radiator in hopes that a small air to liquid cooler will be sufficient.

it is not enough to cool the trans when towing or having much of a load on the motor, also what happens when your motor overheats? yeah your tranny then starts to over heat and the two will compound one another exponentially. i have experienced this. i run dual coolers, one with a on my trans and an inline gauge. (see http://www.toyota-4runner.org/3rd-gen-t4rs/105400-rescue-runner-build-thread.html to look at the coolers)

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Of course you need an extra cooler when hauling a load. Thats why dealers call it a tow PACKAGE because its more than just a hitch install. We agree here too ^

I see temps of around 145-160 while cursing down the freeway at 60+mph even on cool days. some days if its like only 30* out or so i can watch it drop to around 110* if im not moving a lot. but the flip side is if im out wheeling where i dont have a lot of air movement and i have a high/heavy load on the trans -4lo armored and E rated 285s, i can still watch that temp gauge climb well over the 220* mark. i have also overheated my truck in stop and go traffic last summer, while my trans stayed under 200*

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Wow. Nice build but it looks like you went to a lot of trouble and expense to bypass the radiator. I'm guessing your truck would have been better served to use the radiator and then that monster B&M with a fan mounted to it. I would bet dollars to dough nuts that it would work better than what you have now. The key is to lower the fluid temp with the coolant and then bring it lower from there. If you get mud on those two front coolers they will offer little cooling, if at all. Think if you had left the radiator circuit, the 220 would have been more like 180. When your fluid temp rises above 180, the fluid begins to degrade. 220 will certainly be too hot if run for prolonged periods, like offroading.

if i had not bypassed my radiator my dual coolers would have done nothing to help me as you have stated liquid to liquid is a much greater power than air to liquid.

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Not so. Your dual coolers would have lowered the temp an additional 20 degrees each from whatever the radiator was sending through them.

the stock cooler was designed to cool the truck with out a load, meaning not having 5 people in it going up a hill, not having armor on your truck, not having over-sized tires, not towing(even under the towing capacity) and most defiantly not a combination of all of these. the stock cooler is basically useless unless you are a stock rig and never tow. and if you tow and are modified ie lifted, bigger tires, and armored ect i would get rid of the "cooler" in the radiator as you are not creating a weak link in your trans cooling system.

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Are you really serious here?? There are millions of cars and trucks on the road using in-radiator trans coolers that are not leaking or failing thru their entire life cycle. I don't agree with you at all. Just buy a better radiator that's not made by toyota. Problem solved. This is the hysteria I've touched on before. The benefits of an in radiator cooler far outweigh the internet hyped fears of strawberry milkshake.

the plate in the radiator that separates the trans fluid from the antifreeze is weakened everytime temps rise and fluctuate. thats one of the ways these falures are happening over time it weakens the material and you combined that with old age and people not "flushing" their systems, you have a disaster waiting to happen. now the heat differences and extreme temps again are not so much of an issue in a stock rig so i can see the value of keeping they radiator in the "system"

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I bet you sleep with the lights on. Don't you?

One last comment here. Look at the trouble you went through to bypass your radiator. I would guess that the average person deleting their radiator cooler isn't as sophisticated as you and simply buy a $60 B&M and call it a day. Let's be honest here. Your setup is probably about a $300+ modification as a DIY. The twin huge coolers, the fan, the inline temp switch, gauge/pod and extras I can't see in the pictures. Again, I would say this. Buy a new Koyo radiator on ebay for $120 shipped and add a $^0 B&M cooler and you will never have to worry about it again.

My only concern here as a new member on T4r.org (now I question why I even give a crap, for all the heat I'm taking) is that people first understand what they are risking before they go off half-cocked. From what I have noticed from spending some time here, is that more guys than not are tight on money and a major transmission repair would not be in their budget. That's all.

Since I have you ear on this topic, let me ask you a question. Why isn't anyone deleting the mechanical radiator fan on the engine??? That has to be good for at least 5hp and be far more efficient than a mechanical fan at slow speeds. As a tech why haven't you done that with your truck. Seriously the kid I want your input on this.

Drcoffee said:

Of course you need an extra cooler when hauling a load. Thats why dealers call it a tow PACKAGE because its more than just a hitch install. We agree here too ^

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toyota does not install a external trans cooler with their tow packages, its only the wiring and the hitch

Drcoffee said:

Wow. Nice build but it looks like you went to a lot of trouble and expense to bypass the radiator. I'm guessing your truck would have been better served to use the radiator and then that monster B&M with a fan mounted to it. I would bet dollars to dough nuts that it would work better than what you have now. The key is to lower the fluid temp with the coolant and then bring it lower from there. If you get mud on those two front coolers they will offer little cooling, if at all. Think if you had left the radiator circuit, the 220 would have been more like 180. When your fluid temp rises above 180, the fluid begins to degrade. 220 will certainly be too hot if run for prolonged periods, like offroading.

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yes i went to "a lot of work" to bypass the radiator, because id rather spend $120 on tranny coolers and a temp guage than $1500-3400 on a new tranny. and at low speeds i have that fan which dose wonders. i did not replace the radiator because it was not leaking or bad, i just wanted to be safe and eliminate a weak link

Drcoffee said:

Not so. Your dual coolers would have lowered the temp an additional 20 degrees each from whatever the radiator was sending through them.

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yeah probably untill my motor started over heating and then it would start cooking my tranny fluid faster than my dual coolers could cool the temps back down...

Drcoffee said:

Are you really serious here?? There are millions of cars and trucks on the road using in-radiator trans coolers that are not leaking or failing thru their entire life cycle. I don't agree with you at all. Just buy a better radiator that's not made by toyota. Problem solved. This is the hysteria I've touched on before. The benefits of an in radiator cooler far outweigh the internet hyped fears of strawberry milkshake.

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yeah and toyota is not the only one who has this problem either... you are talking about a 15 year old vehicle here. im sure its just all internet hype... ok everyone you heard it hear first get rid of your external coolers and go back to they radiator, it works just fine and we are making a mountain out of a mole hill...

Drcoffee said:

I bet you sleep with the lights on. Don't you?

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sleep is a crutch and i have nods...

tbst said:

I think your argument has derived to being that the radiator cooler is more efficient than the aftermarket cooler.

In your original post you claim that the temperatures will soar above 220 degF if you use just the aftermarket cooler.

Not sure how you can be so sure? I want to believe you, but all evidence points otherwise. Convince me.

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You are just going to dog me all over this forum, aren't you? If you are going to use big words like "derived" use it correctly, will you? I'm not even sure what you are asking.

While you are at it read "the kid" post. He has real life experience as a tech and T4r owner. I'll save you the trouble. And bear in mind that he bypassed his radiator with two huge coolers and a fan on one. and I quote

"some days if its like only 30* out or so i can watch it drop to around 110* if im not moving a lot. but the flip side is if im out wheeling where i dont have a lot of air movement and i have a high/heavy load on the trans -4lo armored and E rated 285s, i can still watch that temp gauge climb well over the 220* mark."

To anyone thinking of deleting your radiator, if you truck doesn't look like this when you are done, rethink it.




A small single cooler will be incapable of cooling the transmission.

Drcoffee said:

Since I have you ear on this topic, let me ask you a question. Why isn't anyone deleting the mechanical radiator fan on the engine??? That has to be good for at least 5hp and be far more efficient than a mechanical fan at slow speeds. As a tech why haven't you done that with your truck. Seriously the kid I want your input on this.

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maybe if you read my build thread (http://www.toyota-4runner.org/3rd-gen-t4rs/105400-rescue-runner-build-thread.html) you might have seen where i said i was going to go to a dual electric fan set up... there are some guys here who have done this. and yes it does work a lot better if you can get it down right. that so far has been the issue, getting the right set up to regulate the fans and to not over cool but be able to keep the motor cool under load.

do a search for electric fans and see what you come up with.

why dont you ask me why as a tech i have not supercharged or turbocharged my runner while your at it...? both of those would be much greater gains than just 5hp...


why have you not installed lockers, or sliders on your rig, why have you not done an LED conversion, that saves power usage.... and if the transmission and stock cooler are of such a worry or issue to you, why have you not converted to a manual transmission, even guys who are not techs have done this, its an easy swap and much safer...

Drcoffee said:

A small single cooler will be incapable of cooling the transmission.

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your obviously not thinking straight... or unable to comprehend things. a small single cooler on a stock rig will do just fine for day to day driving around town and commuting 90% of the time. a single cooler in an armored and lifted rig with any type of a load will be inadequate, you will need something more. but most of our rigs have over 160k miles on them by and large the majority of transmission failures have been due to the "pink milkshake" and not transmission break down due to thermal wear. this is why most people are just eliminating the radiator out of the system or replacing it all together. most people here are not actually trying to cool or regulate their trans temps. the ones who are are either supercharged and or really wheel their rigs on a regular basis.