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Discussion Starter #1 (Edited)
FYI: there were a couple of questions about the flow direction of trans fluid and I hadn't seen a definitive answer, so pardon if this is common knowledge.

In prep for another project & for my personal understanding of the fluid temp management circuit, I put together the image below. Kind of surprising results - at least to me.

Tonight, I'll be having an extra large plate of crow for dinner. I take back everything I was so adamantly convinced of in fluid temp management.

It turns out the "pre-heater" actually DOES preheat fluid from the external cooler before returning it to the trans. In summary:

- Fluid leaves the trans
- Enters the external cooler
- Leaves the cooler
- Enters the heat exchanger
- Leaves the heat exchanger
- Re-enters the trans.

Latest chemistry obviously demands higher operating temperatures than the old Dexron type formula(s).

I couldn't have been more wrong on this one. Perhaps a little hot sauce on that crow will make it more palatable. Maybe a nice fizzy cold beverage too. :act060:

FluidFlow.jpg

Edit: after comments were added by forum members, and subsequent comments in other threads, flow direction remains a bit of a mystery. Text below is added until we have absolute confirmation. Which isn't to say bobcat's contribution to this thread is questioned. Two confirmations is better than one, no?

OTW = oil-to-water heat exchanger sunk in engine coolant at the bottom engine radiator.
OTA = traditional, remotely mounted oil-to-air cooler in front of engine radiator.

The FSM is open to interpretation because "ATF cooler outlet hose" could mean:

A) Outlet from trans to cooler
OR
B) Outlet from cooler to trans

I read it to be B

As a heat management component, the OTW exchanger could be:
A) "pre-cooling" trans fluid before passing to the OTA cooler
OR
B) Bringing trans fluid to a predictable before entering trans

In the case of A:
Because engine temperature is "range constrained" remaining relatively stable around 180f, fluid exiting the trans is likely to be higher than engine coolant temp during normal operation/loads and for most of the vehicles life. As a pre-cooler, the OTW exchanger would be lowering temps before passing to the OTA exchanger - thereby maximizing its (the OTA) ability to drops temps even further before re-entering the trans. In this flow, old school wisdom "cooler is better" fluid temps remain in tact if for no other reason than an OTA exchanger is subject unknown ambient air temps and air flow rates - which is an engineering unknown - but would be "averaged" for predictive service life modeling.

In the case of B:
Fluid hotter than engine coolant enters the OTA exchanger dropping to whatever level it can - based on ambient temps and available air flow - before passing into the OTW exchanger. In this flow direction, the concept of the OTW serving as a "pre-heater" is supported because it is assumed engine coolant heats faster than trans fluid. Aside from that concept and assumption, it would also be a temp "stabilizer" - sending fluid into the trans at a (more or less) predictable temp (engine coolant being "range constrained" operating at a known level) supporting predictive modeling for long term service modeling, if for no other reason than "avg" trans fluid temps below 200f is generically desirable.

Either flow direction seems reasonable from a heat management perspective. Both having variables in heat transfer characteristics of ambient air temps the oil-to-air cooler is operating in, air flow rate and the temp exchange capacity of the the oil-to-water device buried in engine coolant.

In both flow directions, FSM terminology "cooler" is used when referencing both OTW & OTA heat exchangers implying under all circumstances - and in either flow direction - fluid reentering the trans is cooler than when it left (once the vehicle is "at temp").

Ambiguity, much?
 

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I agree, I'd of thought different until the document you found from Allison Transmission, I had just came to a conclusion similar to your direction map above. I'll bring some hot sauce which will make that crow better, I'm calling dibs on the wings ;)
 

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Discussion Starter #3 (Edited)
I agree, I'd of thought different until the document you found from Allison Transmission, I had just came to a conclusion similar to your direction map above. I'll bring some hot sauce which will make that crow better, I'm calling dibs on the wings ;)
The whole concept in my head was upside down. I kept thinking "pre-heat" meant warming hyper cold fluid - and so - I argued the trans spends 99.99% of it's life "at temperature" and any damage from "cold fluid" is inconsequential in such short durations - because a trans is gonna warm itself up right quick. The flow direction makes it clear: hot fluid leaves the trans, the temp is reduced by the external cooler and brought to a predictable temp before re-entering the trans. Makes perfect sense now.

Make it Franks Red Hot, would you? I put that $h!t on everything. LOL.

BTW: it's still a mystery why this concept isn't as widely known as other areas of automotive design. Engine oil viscosity, tires, component metallurgy, ETC, ETC, ETC. Seems as though this particular subject is not well understood in the enthusiast community.
 

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Since I know you have the data. Would you mind posting what the temps were vs the dash outside temp. Unless you take it to Big Bear or further north you can't get a below freezing ambient temp or below zero temp. I'm thinking this is obvious but after everything is up to operating tempature.
 

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Discussion Starter #5
Since I know you have the data. Would you mind posting what the temps were vs the dash outside temp. Unless you take it to Big Bear or further north you can't get a below freezing ambient temp or below zero temp. I'm thinking this is obvious but after everything is up to operating tempature.
The temps I have (somewhere) were taken with a laser temp gun at the exchange ports and cooler lines. Not real confident in those because the readings danced all over as the laser moved very short distances on the width & length of the fittings/hoses. I'll find them but don't trust them. The driver side port is especially hard to get a stable reading from cuz its nearly invisible from up top.

But there's a solution in the works that should provide some excellent data. More on that later.
 

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Thanks for the work!! Ive been looking for several years now without success for a post I read on on a Subaru WRX forum. The bypass debate had been going on for many pages. Different vehicle and of course everything you read on the internet is true, but this study appeared be genuine and accurately performed.

This person slipped as many as 15 thermo-couples under engine coolant and ATF connections and then used data collection hardware and modeling software to graph it out under quite a few conditions. His conclusion was that indeed the ATF heat exchanger cooled ATF under some conditions and heated it in others in some sort of engineered balancing act, but in general spent more time cooling ATF than warming it.

That is why Ive not been on the "simply bypass it" bandwagon. Such a study is a decent amount of work, but not huge...just my employer wouldn't appreciate me borrowing the equipment.

It was interesting that despite his attempt to resolve the question at least with regard to his particular model vehicle, that the debate continued to go on without anyone else having any real data. The guy eventually made a comment similar to "are you interested in any more of my data" and a few replied with great appreciation and then the thread resumed with its yes/no bypass debate. Perhaps he just figured no one was interested in real data and deleted the post? I do wish I could find it because it was very detailed with hot and cold starts, and quite a few graphs where all the lines of data crossed and intersected. This was 5 years ago when I first added my ATF temp gauge and filter.
 

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Well, if there is anything you can do to help, OhSix. Let me know
 

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Discussion Starter #8
Thanks for the work!! Ive been looking for several years now without success for a post I read on on a Subaru WRX forum. The bypass debate had been going on for many pages. Different vehicle and of course everything you read on the internet is true, but this study appeared be genuine and accurately performed.

This person slipped as many as 15 thermo-couples under engine coolant and ATF connections and then used data collection hardware and modeling software to graph it out under quite a few conditions. His conclusion was that indeed the ATF heat exchanger cooled ATF under some conditions and heated it in others in some sort of engineered balancing act, but in general spent more time cooling ATF than warming it.

That is why Ive not been on the "simply bypass it" bandwagon. Such a study is a decent amount of work, but not huge...just my employer wouldn't appreciate me borrowing the equipment.

It was interesting that despite his attempt to resolve the question at least with regard to his particular model vehicle, that the debate continued to go on without any real data.
Mr. Schwejo, in your travels, have you come across detailed information pertaining to trans fluid temp control in modern vehicles?

Reason I ask: historically, trans fluid temp has always been: HEAT BAD, COOL GOOD. This fluid circuit design turns that model upside down. If the RL design is representative of modern implementation - it looks as though the fluid entering the heat exchanger is "too cool" so is warmed (or stabilized) before returning to the trans. I've searched the ASE site and hunted for information on fluid thermodynamics - coming across only one "warning" reference to cool trans fluid. Found here in Allison Trans TSB's.

IMO, the most baffling aspect of this automotive design is why is this not more widely understood by people like us, who actually want to understand such basic/critical information for extending the life of our beloved vehicles?

Apparently, the lack of information has caused controversy on nearly every vehicle forum as enthusiasts try to cram their understanding into current industry practices. Billions and billions of pixels dedicated to discussing a gross misunderstanding/lack of information and spewing opinion based solutions that potentially cause more harm than good. I was certainly a proponent of by-passing the heat exchanger in the RL rad. After seeing the intent of the design in a graphic, I've done a 180 on that ill informed opinion.

I'm no conspiracy theorist, but its almost like the industry is trying to keep this topic secret. Frigging weird.
 

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Good work OhSix. That flow is backwards from how I envisioned it.

Let me repost part of your post and add the connections:

- Fluid leaves the trans (via the C connection)
- Enters the external cooler
- Leaves the cooler (via the B connection)
- Enters the heat exchanger (via the B connection)
- Leaves the heat exchanger (via the A connection)
- Re-enters the trans. (via the A connection)



Note: the ATF cooler is separate from the radiator. The heat exchanger is integral with the radiator.

If I understand your conclusion, the problem with by-passing the heat exchanger is that the transmission fluid will be too cool for optimal transmission operations, in normal conditions. So the heat exchanger serves as a means to regulate and stabilize transmission fluid temperature before it returns to the transmission.

Do I understand correctly?
 
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I guess this is pretty confusing -my understanding is that most vehicles would have flow from transmission going first to radiators cooling section and then to external air flow cooler and then back to transmission -this shows flow opposite to that -doesnt seem correct for ridgeline -i guess to know for sure would have to unhook line and check actual flow.
 

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Discussion Starter #11 (Edited)
Good work OhSix. That flow is backwards from how I envisioned it.

Let me repost part of your post and add the connections:

- Fluid leaves the trans (via the C connection)
- Enters the external cooler
- Leaves the cooler (via the B connection)
- Enters the heat exchanger (via the B connection)
- Leaves the heat exchanger (via the A connection)
- Re-enters the trans. (via the A connection)



Note: the ATF cooler is separate from the radiator. The heat exchanger is integral with the radiator.

If I understand your conclusion, the problem with by-passing the heat exchanger is that the transmission fluid will be too cool for optimal transmission operations, in normal conditions. So the heat exchanger serves as a means to regulate and normalize transmission fluid temperature before it returns to the transmission.

Do I understand correctly?
14-241 refers to the driver side port "A" of the exchanger in the RAD as "ATF cooler outlet". I was trying to maintain Honda syntax.

I'm away from the manual so don't know what term they use to describe the external cooler.

BTW: answering your edit. YES. That's the conclusion. Based on the term in the FSM, the fluid passes from the remote air cooler to the heat exchanger in the bottom of the RAD. It seems logical to conclude the fluid is cooler at that point than optimal, so thermal optimization happens as the fluid passes thru the exchanger before entering the trans. The sum total of alloys and hydraulics must "need" fluid designed to handle the upper and lower extremes predicated by engineering parameters.

The crow I had for dinner last night wasn't nearly as bitter as expected. LOL
 

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In point of fact, Honda calls it the ATF Cooler. ;)



Somewhere I recall seeing a depiction of the front of the RL with radiator and ATF cooler showing. I can't find that image at the moment.
 

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Mr. Schwejo, in your travels, have you come across detailed information pertaining to trans fluid temp control in modern vehicles?

Reason I ask: historically, trans fluid temp has always been: HEAT BAD, COOL GOOD. This fluid circuit design turns that model upside down. If the RL design is representative of modern implementation - it looks as though the fluid entering the heat exchanger is "too cool" so is warmed (or stabilized) before returning to the trans. I've searched the ASE site and hunted for information on fluid thermodynamics - coming across only one "warning" reference to cool trans fluid. Found here in Allison Trans TSB's.

IMO, the most baffling aspect of this automotive design is why is this not more widely understood by people like us, who actually want to understand such basic/critical information for extending the life of our beloved vehicles?

Apparently, the lack of information has caused controversy on nearly every vehicle forum as enthusiasts try to cram their understanding into current industry practices. Billions and billions of pixels dedicated to discussing a gross misunderstanding/lack of information and spewing opinion based solutions that potentially cause more harm than good. I was certainly a proponent of by-passing the heat exchanger in the RL rad. After seeing the intent of the design in a graphic, I've done a 180 on that ill informed opinion.

I'm no conspiracy theorist, but its almost like the industry is trying to keep this topic secret. Frigging weird.
Wish I had some real industry insight on this. You sure are right that there seems to be such a lack of any real concrete engineering information. strange when we seem to have endless data on practically everything else. I read that the there is a minimum ATF temp needed for torque converter lockup which of course could assist in meeting overall industry mileage requirements... but we all know an unlocked torque converter produces huge amounts of heat and reaches operating temps very quickly, except perhaps in very cold climates? I suspect in my temperate climate it doesn't make much difference.

Here is my experience with adding a ATF temp gauge. My apologies that its a bit of a diversion from the thread topic, but I went through your similar flow analyses during installation. Ive never had the ATF over temp indicator light up despite driving over the road in the thread pics at over 100 deg temps on later occasions. I just leave it in drive. Seems folks at the time were downshifting or needlessly locking the transmission and having it overheat, and i just wanted a gauge to be able to monitor things. Perhaps a ScanGauge can read ATF temp on newer Ridgelines but not for 2006.

http://www.ridgelineownersclub.com/forums/showthread.php?t=90458&highlight=guage&page=2
 

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Discussion Starter #15
In point of fact, Honda calls it the ATF Cooler. ;)



Somewhere I recall seeing a depiction of the front of the RL with radiator and ATF cooler showing. I can't find that image at the moment.
It appears the FSM refers to BOTH air & fluid radiators as "coolers".

This from 14-235:

14-235.jpg
 

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Discussion Starter #16
I guess this is pretty confusing -my understanding is that most vehicles would have flow from transmission going first to radiators cooling section and then to external air flow cooler and then back to transmission -this shows flow opposite to that -doesnt seem correct for ridgeline -i guess to know for sure would have to unhook line and check actual flow.
It's pretty clear (to me at least) the flow is described in the service manual. I agree, for quite some time I argued the concept of "heating" trans fluid to engine temp made no sense because, historically, trans fluid *needs to be* cooler than the engine average. After having my ill-informed deduction challenged by several forum members here - based solely on - "Honda wouldn't do it if it weren't needed" OR "I trust Honda engineers more than what a bunch of internet yahoo's think", I looked farther into the topic of "pre-heating". None of it made sense because there is so LITTLE information available to the public on this aspect of design. Searching ASE and other resources, only ONE reference to optimum temp management was found, a service tip issued by Allison transmissions.

Then, digging into the manual, the images in the OP of this thread started to make sense. IF the design goal is to maintain a predictable thermal value at the input side of the trans under *any-and-all* environmental conditions (desert, city, sub zero) it makes perfect sense engine temperature is the place to get it. Engines, regardless of external temps, tend to operate within a finite range that can be used for other reasons - in this case, providing a known value (or range) with which to pass hydraulic temps into the pump of a trans. With fluids, alloys and materials inside the trans optimized to operate in the same range as the engine, you have an excellent engineered solution to providing a reliable, (more or less) constant fluid temp to supply the tranny. This likely explains the VERY long service life of the tranny many owners have reported.

The PROBLEM is the execution of mechanical components that - upon failure - allow incompatible fluids to mix. Hence, the on-going battle with SMOD.

OEM's clearly have limitations with every part of a vehicle. Their primary concern being: reliability within and (to a point) beyond warranty.

The only reason to design for high reliability in-warranty is to lower claims against accrued warranty funds. The only reason to exceed warranty reliability is to build the brand name, but there's a limited to how far that goes.

IF Honda and other OEM's wanted to, they could design an interface accomplishing heat management goals without allowing the kind of catastrophic failures some unfortunate owners have experienced, but that cost is too high for the actuarial function of warranty accrual. SO, we pay the price when/if that failure happens.

So far, the best solution I've seen to this issue is the suggestion from speedlever. Simply replace the RAD at A-14 service and be done with it. It's a marginal additional part cost at that time, things are already apart, so labor is partially paid for (either in $ or sweat) so get it done and be confident you've safe guarded your investment.

The only caveat I can think are these: we've seen owners with well under 115K experience SMOD. There is almost no way to reliably detect a pending failure AND IF it happens, stopping the vehicle immediately greatly increases the change of saving the trans.
 

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Have to wonder if by now automakers could not engineer thermal control to keep the ATF optimal for all conditions without relying on the radiator connection.
The cost alone of the transmission and it's complexity seems compromised even when everything is working right when you throw it's fate on to a $200 radiator.
 

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Just double checked actual flow direction on my ridge -it is opposite of diagram shown in original post. Flow goes from the lower of the two transmission metal lines into the driver side radiator line -goes through internal radiator cooling section then out the radiator passenger side line-then goes into auxillary cooler lower line -then out aux cooler upper line and back into transmission via the upper transmission metal line -this is actual measured flow -pumped a qt. in about 4-5 sec - this is opposite direction of diagram in this post.Must be that diagram does not apply to Ridgeline, my fsm never shows flow direction anywhere in manual that I can find.
 

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Discussion Starter #19
Just double checked actual flow direction on my ridge -it is opposite of diagram shown in original post. Flow goes from the lower of the two transmission metal lines into the driver side radiator line -goes through internal radiator cooling section then out the radiator passenger side line-then goes into auxillary cooler lower line -then out aux cooler upper line and back into transmission via the upper transmission metal line -this is actual measured flow -pumped a qt. in about 4-5 sec - this is opposite direction of diagram in this post.Must be that diagram does not apply to Ridgeline, my fsm never shows flow direction anywhere in manual that I can find.
To be clear: the flow direction in the OP was drawn by me. That direction was derived from terminology in the FSM, I find no specific reference to flow direction anywhere in the manual. After seeing speedlever's reply, went back to the FSM for a 3rd & 4th look. It's possible I misread the diagram titled "ATF Cooler Outlet Hose Replacement" 1. on 14-241. Please check and confirm for yourself.

The direction you observed would suggest hot fluid leaves the trans to be (theoretically) cooled to engine temp, then further cooled by the air cooler before returning to the trans. In light of the latest A$$umptions on my part, this seems odd - only because of a self described logical conclusion that temp control is better controlled by a range of fluid temps (engine coolant) vs. air temp covering a much broader - and therefore unknown - temp range.

FSM14-241.jpg
 

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Ohsix, I think what is intended is that cold transmission fluid is brought up to operating temp more quickly by routing it through radiator first as radiator/coolent temp will rise more quickly than transmission fluid temp under normal conditions -then auxillary cooler will remove some of that heat prior to return to transmission. As I researched this on web I found many references to this being the normal/most common way transmission fluid flows ie; first to radiator/cooling section, secondly to auxillary cooler then back to transmission and my ridgeline definitely flows that way- I have checked twice now as I installed a magnafine transmission filter in return line and wanted to be certain on flow direction -guess you dont have to eat crow after all?
 
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